Throttle Position During Acceleration and its effect on FE [ Archive] - GasSavers.org

SVOboy

09-05-2005, 10:50 AM

You'll get the best efficiency
around town by accelerating with full throttle, and shifting up to
the next gear quickly, before engine RPMs rise too high.
There are
two reason why this works. One is that the higher the gear, the lower
the frictional losses. By getting to 5th quickly, the total number
of engine revolutions is reduced, with a corresponding reduction in
frictional losses. The second reason is pumping losses. This is the
work done to force air past a partially closed throttle plate. The
more closed the throttle is, the higher the losses. Accelerating quickly
reduces throttle losses, because the throttle is open. In addition,
engine speed is lower in fifth, so to generate the same amount of
power, you have a larger throttle opening (and hence lower throttle
losses) - this is another reason to get to higher gears as quickly
as possible.
The best fuel economy is gained
by a combination of the gas petal to the floor with shifts at as low
an rpm as possible to sustain your desired acceleration. This ensures
a fully open throttle during the entire acceleration event and gets
you out of the lower gears as quickly as possible, for lower frictional
losses. It also gives you even more electric motor assist, as the
acceleration takes longer. There is only one problem with this technique
- its virtually impossible to do. You have to shift like a race car
driver, except that the shifts are at low rpm instead of high rpm.
You wind up going through gears like a maniac. It can be a lot of
fun, but you have to be really involved with driving (no cell phones)
and the technique is extremely counterintuitive. The combination of
mashing the accelerator and shifting at 2500 or 3000 rpm just doesn't
feel right. However, if someone is willing to practice this, they
can get a nice boost in FE around town.
After accelerating this way in
1st & 2nd gears, you'll often be up to your desired cruising speeds.
Now it is time to switch modes, using as little energy as possible
to maintain this speed. Typically you'll now want to be in fifth gear.
The 1-2-5 shift pattern (or 1-2-4 as the case may
be) may seem strange at first. After all, why are those other gears
there if you shouldn't use them? The answer is to think of them as
passing gears or cruising at slower speed gears. In most cases, this
is the way I use the five gears:
<blockquote>
1: Accelerating
gear 
2: Accelerating gear 
3: Even slower cruising / quick passing gear 
4: Slow cruising / slower passing gear 
5: Cruising gear
</blockquote>
Once you're up to speed, in addition
to quickly getting into your cruising gear, you'll also want to begin
feathering the throttle. Since you should have done all your acceleration
before going into cruising gear, you now want to use as light a throttle
as possible that will still maintain your current speed. If you find
that you want to accelerate further, you may be better to downshift
for a quick blip of acceleration, and then shift back into your cruising
gear.  Does this sound right? Am I crazy? Slam it to 50 mpg in second then shift into 5th? Huh? What? It is from insightcentral so they know their stuff, but really?

diamondlarry

09-05-2005, 11:40 AM

I have heard of this technique before so I think you are probably on the right track. This is the technique that I normally use but have never thought to test the mileage differences between "normal" shifting and this method. Depending on conditions, I either do 1-2-5, 1-3-5 or some variation. I rarely use all 5 gears unless I am puuling onto a crowded highway.

Matt Timion

09-05-2005, 11:41 AM

I've actually done this before.  The difference for me, however, is that I didn't take it up to 50mph in 2nd gear.  I took the 87 CRX Si to about 3000rpm and them went into fifth gear for cruising around town.  I followed the 1-2-5 pattern.The engine didn't mind at all.  Performance wasn't affected.  A few other times I've just skipped 4th gear and done 1-2-3-5.I usually save about 500 RPM by crusing around in 5th gear, so it's worth it to me. Now, the WOT theory is something I'm not sure about.  For the insight I believe flooring the gas will click on electric assist (their electric motor will give an extra 10hp when it's assisting the gas motor), thus making it easier to accelerate and also will not affect their gas mileage as much as WOT affects a standard car's gas mileage.  So in reality the insight owners are cheating a little with their little electric motor.I think moderate acceleration and the 1-2-5, 1-2-3-5, or 1-3-5 shifting pattern is going to help a lot more than WOT.

SVOboy

09-05-2005, 11:49 AM

I agree with everything that has been said, it is just I wonder how much difference it will make. Sometimes is I have to hustle I will rev to 2500 and skip a gear but usually I just 2000 all the way. I can't test it out myself because I'm auto (for the time being), but hopefully some sort of test can be figured out, though I think it should be pretty hard to pull off.

Matt Timion

09-05-2005, 12:25 PM

Eventually it would be a fun test to do one tank of 1-2-3-4-5 shifting (and never to cruise in 5th in the city) and another tank of 1-2-5 shifting.  I think that this is doable down the road as an experiment.

SVOboy

09-29-2005, 09:48 AM

Yeah, I tried 1-2-5 WOT shifting today and not only did I take off like crazy so that it would be impossible to do under normal traffic and [i]I just don't understand. Can anyone tell me why this would help for gas mileage? It seems like the camry musta dumped a cup of gas in there when I had it at WOT for those 4 seconds. It was fun though, but not worth getting 20 mpg.

Flatland2D

09-29-2005, 01:38 PM

I have a suspicion that the fuel mix goes way rich during this style of driving. It might be more efficient to accelerate when the engine is actually producing some power (~3000rpm) so it doesn't have to compensate with the mix. It's just an idea though. Hopefully I can test this when I install my AFR gauge.

SVOboy

09-29-2005, 03:12 PM

That actually makes a lot of sense to test it then, good thinking.

SVOboy

10-08-2005, 05:04 PM

So, guess what? In my quest for ecu tuning I found this thing that says WOT acceleration is the best for gas mileage, and some who say it is, whaddya think about either side of the argument:

<a href=http://forum.pgmfi.org/viewtopic.php?t=7342&highlight=fuel+economy target=_blank>PGMFI Stuff</a>

Flatland2D

10-08-2005, 11:30 PM

Can you copy and paste? You have to register to view that link. I've got nothing against that, I'm just lazy.

Only way to know for sure is to test it.

SVOboy

10-09-2005, 08:09 AM

A naturally asperated gasoline engine is most efficient at FULL THROTTLE. If you are getting on the freeway, or are getting up to speed to cruise for a while, then you will get better gas mileage in the long run, if you accererate as fast as possible (full throttle) up to cruising speeds.

Also, around 50 mph, the air resistance / speed curve starts to rise exponentially. So, in theory, the closer to around 50 you cruise, the better mileage. In other words, don't speed.

I believe this would only be true if full throttle was mapped to 15:1 AFR Wink

The extra fuel at WOT far out weighs the pumping losses saving.

I'll usually take the car to cruising speeds, 60 then 70 then 80 and lean out to 15:1. As far as timing, I'll advance a degree or two when cruising, listening intensely for any sort of knock. I've tuned my buddy's cars like this he is getting 420 miles to the tank in a Integra with a B18C5 bottom end, so the math on that is like 35mpg.

I feel there will be a point of diminishing returns on lean burn, but every application is different. Mine does not like lean ratios. Itâ€™s happier in mid 14â€™s, but it still makes 35/gal on half city half hwy â€“ b18c1.

What about injector pressure? RC injectors will supposedly hold up to 100 lbs according to RCeng, but then again, is that the best atomizing injector? I doubt it.

And Iâ€™m sorry, there is no way in hell full throttle is more efficient than part throttle. Iâ€™m sure bsfc may be lowest with somewhat higher manifold pressure than cruising, but add in the fuel ratios for open loop and extra heat and friction at full throttle and you have wasted work.

If you're open minded, then how about:

Tire pressure
No ac
Windows up
Lower coefficient of drag??
Are iridium plugs hype?
fuel rail heater
Ignition system
and of course, precise timing.

That's all I can think of.

Those are the things with any meaning from that thread. I kind of carried on with that question of leaning at cruising speeds, but I have been told for dpfi that's really not a thing to do (tuning at all). So I dunno, I might just see if I can get a decently priced hf/vx mpfi system.

SVOboy

10-23-2005, 09:43 PM

Me: What about this idea that wot acceleration is better for mileage cuz of less resistance on the throttle?
DrDisco: it's due to pumping losses
DrDisco: the engine has to work to pull a vacuum at anything less than wot
Me: Is it true though?
DrDisco: yes
DrDisco: i tried something though
Me: So if I floor it and shift early I'll get better mileage?
DrDisco: in my accord, i tried using wot as much as possible to accelerate and shifted early, and i couldn't tell any difference in mileage
Me: Dang.
DrDisco: yeah
Me: I spose I can't shift early in an auto.
DrDisco: not really
Me: The insight people use WOT and a 1-2-5 pattern.
DrDisco: interesting
DrDisco: gets better mileage?
Me: They say so.
DrDisco: hmm
Me: I'm wondering if I tinker with the WOT fuel and lean it out a bit then I'll reduce pumping losses and fuel shot in there.
Me: Eh?
DrDisco: sounds right to me
Me: Sweeeeeeeet.

DaX

11-08-2005, 06:56 AM

Whoever said the extra fuel added at WOT outweighs the pumping losses is right. On a speed density system [sorry, Honda's are pretty much all I know], when you go to WOT, your manifold pressure goes pretty much to 0 psig. Your MAP sensor takes note of this and tells the ECU your car is in a 'high load' situation, which then tells the injectors to start widening their pulsewidth and dump more fuel. This is actually very intuitive - when you want to accelerate, you say 'step on it' [go to WOT] - it takes power to accelerate, and it takes burning more fuel to make power.

SVOboy

11-08-2005, 12:24 PM

Can we honda people, however, not lean the hell out of our WOT fuel maps?

rh77

11-08-2005, 01:31 PM

On my '99 Acura TL I use the auto-stick to try to keep the 4-speed auto in the top gear and give it as much throttle as possible, especially WOT -- like getting it into 4th gear up the on-ramp, floor-it, and gradually get up to speed. Is this acutally killing my fuel economy? I've been doing this for a long time since it provides smooth acceleration and I thought that, at WOT, it was running at peak efficiency. So, Honda's fuel maps are probably creating an "open-loop" and ruining the whole deal, right? Bummer.

RH77

SVOboy

01-15-2006, 11:58 AM

The theory goes that although gas is related to RPM x throttle position, the amount of gas burnt going WOT to 60mph in 8 seconds may still be less than if using all 5 gears to get to 60 at light throttle taking 20 seconds.
Also when driving stick, at closed throttle and the RPMs are going down, like on a hill, if your still in gear, the engine uses no fuel at all, simply the engine is acting as a air pump till it falls to 1100 or you throw in the clutch. Sensors and modern technology do that.
When driving on the highway, build up speed before a hill with more than crusing throttle. On the hill, keep the throttle constant to where your barely loosing speed. then over the hill, go light (maybe off) the throttle. at this downhill, your using almost no gas. then use light throttle down the hill to build speed before the next hill.

If you drive like some kid in a racecar, you can really make youre MPG terrible. but if you know how your car works, you can kick the MPG up real high. Like this one guy with his Honda Insight got over 100mpg, however thats called 'driving with the intent to get good mileage' and may not work like in Atlanta where I am.

*scratch*

philmcneal

05-04-2006, 02:32 AM

indeed this is a topic i'm trying to figure out on my own.

1/3 open throttle and 2000 rpms shifts? (my engine does not like low luggy rpms like 1500 in 3rd will consume more gas than in 2000 rpms)

or following the recommended shifts points in my manual book?

15 mph (24 km/h) 2nd gear 3300 rpms drops to 1700 rpms
27 mph (43 km/h) 3rd gear 3000 rpms drops to 1800 rpms
39 mph (63 km/h) 4th gear 2500 rpms drops to 2100 rpms
53 mph (83 km/h) 5th gear 2500 rpms drops to 2100 rpms

seems like honda really wants me to to keep it between 2000 and 3000 rpm i can see why. If you lightly touch the throttle at anything higher than 1700 rpms the MPG meter will spike for the better. Anything lower than that rpm (with the exception of 5th gear and sometimes 4th until it goes below 1500 rpms) and any input on the throttle and i'll be using more gas than usual just to pull the engine (so lugging in theory). I have a bad habit of trying to keep rpms too low and maybe that's why when I stop I really mess up my average?

argh one of the only bottlenecks from preventing me from getting good mileage besides the DIY mods.

it seems at low rpms accelerating, i use more gas to produce an x amount of pulling power which is pretty low if you ask me. BUt at a higher rpms, I eat almost as same amount of gas but the pull is much greater.... hm.........

no real answer argh!

MetroMPG

05-04-2006, 07:30 AM

no real answer argh!

has no one (with FE instrumentation) on any forum done any *systematic* testing of different acceleration techniques? (i thought i read on cleanmpg that brick was thinking about testing this...)

it's hard to do (control properly) - that's one reason. also it's likely one of those things that's different depending on the car, so there's no "one technique fits all" answer.

also, i suspect what accel technique is best depends on what comes immediately *after* the acceleration:

WOT (or near WOT) is definitely bad if... you have to stop or slow down again shortly after you finish accelerating. there's no question that WOT or near-WOT short-shifting uses more fuel than very slow & gentle accel. i doubt WOT makes sense for typical "city" driving.

WOT (or near WOT) may be good if ... you have an opportunity to coast or cruise for a long period after accelerating. i sometimes accelerate harder than normal just to set up a longer engine-off coast. but that's just my gut telling me it's better, and i have no proof.

i don't really know. and i haven't had any coffee yet.

brick

05-04-2006, 08:02 AM

i don't really know. and i haven't had any coffee yet.

I've had two cups this morning and I don't know, either. I was thinking about attempting some kind of controlled test but it's difficult for the reasons that you describe. There are so many variables! Shift points are one variable, throttle position is another, and conditions are a whole set of variables including terrain, traffic, upcoming obstacles, etc.

I read Phil's post earlier and went to check the owner's manual for the Accord. They actually give two sets of shift points: one for "normal" acceleration and one for "cruising" acceleration. "Cruise" shift points for my 2.3L engine are somewhere in the 2200-2500RPM range. (I can't be sure since they do it by speed and I'm not quite good enough to do the conversion off the top of my head.)

MetroMPG

05-04-2006, 08:26 AM

rh77

05-04-2006, 10:06 AM

I've had two cups this morning and I don't know, either.

:D

i should go check my manual...

nothing helpful. these cars didn't come standard with a tach, so there's nothing about suggested RPM for shifting.

it does say:

"Shift Light (US only): if you have a manual transaxle, you have a shift light...for best fuel economy, accelerate slowly and shift when the light comes on."

The manual should say something like "Don't make jack-rabbit starts and stops, but do not accelerate too slowly" -- basically you need to get into that higher gear as quickly and efficiently as possible. With the auto-trans, I generally give it 20% on the throttle (without A/C) and climb to the needed speed. Immediately when it shifts, the MPGs jump up by double. It's a technique, for sure -- which I haven't mastered.

Oh...and I had my Triple-Shot Espresso in my Almond Mochacinno this morning, so I'm up to normal operating specifications ;-)

MetroMPG

05-04-2006, 10:39 AM

The manual should say something like "Don't make jack-rabbit starts and stops, but do not accelerate too slowly"

i've often seen the jack-rabbit warning, but never anything about accelerating "too slowly".

-- basically you need to get into that higher gear as quickly and efficiently as possible.

i don't think you can generalize on this point. depends on what's coming up next in your driving (e.g. imminent stop/slow down). also, there are likely differences in what technique is best depending on manual or auto.

krousdb

05-04-2006, 01:22 PM

philmcneal

05-04-2006, 04:31 PM

I did some very limited testing with the Del Sol. I started one of my morning commutes using aggressive acceleration to get up to speed and then normal 5th gear driving from there. When I say aggressive, i mean about 1/2 throttle, not WOT but much more than I normally use. Anyway, by the time I got to my 2nd milestone, my FE was so much below my normal targets that I stopped the test and went back to normal driving technique. It wasn't worth killing the tank FE any further. I wish I had the data to present, but my fading memory says I was 10-20% below normal by the second milestone.

agreed, I quote from my post from cleanmpg:

__________________________________________
I think i cracked it to why Wayne perfers super slow acceleration. The high mpg rates (35 mpg +) never bought down my average as it would do if I were to follow the manual's way to acccelerate (5-15 mpg). Here's what I discovered:

1st gear littlest amount of throttle possible (20-25 mpg rates) up to 2000 rpms

Shift (now wayne perfers the fast shift so that he doesn't lose velocity, since I'm a noob I shift slow and wait for the clutch to be done its buisness before attempting to accelerate since I can't afford a clutch job)

2nd gear should be down to 1000 rpms again, now extremely little throttle (30 -35 mpg rates) and your speed should climb slowly, we talking about like 1 kilometers per hour per second! but your patience will be rewarded as your instantenous mpg goes up along with it! climbing by 2 points as you get up to speed oh here comes 2000 rpms again!

Shift (i sometimes clutch in, go into neutral and wait for the revs to drop before sliding it into 3rd to make the sync, although its much harder to do when your revs are so low and the difference is not that great)

3rd gear revs should drop to 1500 rpms, now the littest amount of throttle possible (first trying just to maintain rpms, then slowly rising up slow) and then your speed will increase by 1 kph again (those using miles it could be harder to judge since your numbers mean a lot!) and these mpg rates will be around 35 - 45 mpg rates and then another battle to 2000 rpms!

Shift (ok from 3rd to 4th for some odd reason, is the easist gear out of them all. The motion of just "Down" and the difference in rpms is so little that this shift is just the easist to master, I don't know I guess you can say this shift is the fastest shift I'll do without losing speed like my first 3.)

4th gear now this is where it gets exciting! back down to 1500 rpms, and climbing slowly by 1 kph again. But rates are at 45-60 mpg almost and even when climbing a small incline or some sort, I don't even have to downshift (unless i'm down to 1000 again) because apparently the small pull is still good enough, although with the mpg meter minus 5-10 depending on the incline and then going back up as the road steadies itself, but still very good! Even when reaching as high as 2000 rpms you can start to see the max mpg i can get 60 + and then starts to drop again as you climb over 2000 rpms... kinda cool.

Shift (now from 4th to 5th is a little odd, the drop is quite big and I'm glad it is because I have a decent overdrive to boot! When above 2000 rpms (highway reasons) when shifting I do the sliding in the neutral trick and wait for revs to drop before shoving it into 5th with no risistance (i hate that feeling, why should a gear reisist to be selected? because its not ready yet!).

5th overdrive (drops to 1500 rpms): Depending on the revs, my mpgs can be as high as 100 when giving the littlist throttle possible, or as much as 50 mpg if I'm climbing a small incline. What I like about 5th is when you climb inclines with 5th, your speed bleeds a lot less as opposed to in 4th, this definately tells me there's less friction to battle at 5th for sure! Just the gearing for the overdrive is so deep is that we have to make sure never to lug it (under 40 mpg instanteous) but using 5th to MAINTAIN or BLEED off speed is okay and should be done if you want to save some brakes!

So lession of the day is, what the book recommends is the best ACCELERATION TO EFFICENCY RATIO and what WE want is HIGH FUEL EFFICENCY WITH NO MENTION TO TIME WHATsoEVER. Since I drive in the heart of the city and red lights are a commonblode to me (I don't think I've timed all the green lights yet... maybe one day) so I think I'll be practicing more of this type of acceleration just because it does not dent my average ever and I'll never see anything below 40 mpg!!!!! AVERAGE ;D

but hey this is just a civic ;)

_________________________________

MetroMPG

05-04-2006, 07:23 PM

your speed should climb slowly, we talking about like 1 kilometers per hour per second!

are you some kind of crazy person? you're a speed freak compared to my rates of acceleration!

seriously, good info phil. thanks for cross-posting that.

philmcneal

05-05-2006, 01:44 AM

and the stats bleh i pretty much memorized it: conversion is through my head so correct me if i'm wrong

2300 rpms MAX (oh yeah ~~)
4.9 LPK or 47 MPG
64 Km/h MAX or 40 mph
35 km/h AVG or 25 mph
8.7 KM drive (5.3 miles)
12 minute drive
88 max coolant temp (C) (max is 90)
2 stop signs
9 turns
9 lights
gone through 5 green lights
4 1st gear starting out
4 FAS ( bump started before my momentum dropped below 30 km/h then idled for less than 10 seconds before 1st gear start)
.4 liters consumed (.1 gallons)

on my way home wasn't as pretty, since i dediced instead of FASing, i'm going to give little throttle for 5th gear instead (at least i'm saving gas legally)

5.8 LPK (40 mpg)
2400 RPMS MAX
64 km/h max
40 km/h average
9.3 km drive (5.5 miles)
15 minute drive
90 max coolant temp
1 stop signs
5 turns
11 lights
2 minute construction work idling wait
7 1st gear starts (ouch... everyone went fast and made the green and i slowed poked to stop at it :(
0 FAS :O
.6 liters consumed (.2 gallons)

bleh blah shifting sucks. I wish there was an abusable CVT in which I can FAS and then regen energy if I needed to stop, one can dream. Also with no FAS my battery voltage stayed at a high 13.5 volts than its ususal 12.8 volts... but since I leave the car outside (too lazy to call the house to open the garage, and FAS into my driveway is too bumpy) i'm sure it will stablelize itself back into the 12 volt area as tempeartures go down and up again.

edit: i forgot to add and i thought it was equally as important. As you shift to the next gear and slow accelerate towards 2000 rpms (1 kph per second) I notice as the MAP starts out around 6.5 to 7 but as you increase the speed that number drops in .3 increments allowing your FE to jump up. As more speed is built upon, that same pressure on the throttle magically goes lower and lower as maybe the ECU finally realized that "hey I want to really conserve fuel man! Light off the pressure!" and slowly as you gain speed that exactly what happens! when I reached in MAPS of under 5.5 then looking at the tach i'm at 2000 rpms and then the MAP will increase over 6 again (higher fuel consumption)!

Shift!

DaX

05-05-2006, 12:21 PM

1 kilometers per hour per second!

haha, what a weird unit of acceleration! :)

Randy

05-06-2006, 12:49 AM

I think there's something special about the Insight that keeps WOT from ruining mileage. Nearly all cars run rich mixtures for extra power (max power is slightly richer than stoichiometric, max mileage slightly less). Back in the days of carbs, low vacuum would open the 'power valve', which was like increasing the main jet size. Computers do the same thing, but without the cool name.

Supposedly most cars run most efficiently just below this enrichment point... maybe 80% throttle.

rh77

05-06-2006, 05:15 PM

So, that's 0.62137 MPH per second?

I think I do about 2 mph per second, or good grief: 3.24 Km/H/Sec!

MetroMPG

05-06-2006, 05:24 PM

the toronto star newspaper ran a "how to drive efficiently" article today that recommended WOT & short-shifting.

i wrote to the author for more info on the source of the "studies" he mentions in support of WOT, and got this reply (within an hour, which was a surprise):

BMW pioneered the WOT method back in the '80s and found it gave better fuel economy. It first appeared in a Road & Track article at about the same time. You can access older Road & Track articles through their website I believe. BMW would probably allow the public access to that information as well. The idea behind it is internal combustion engines are very inefficient at part throttle settings and most efficient at wide open throttle. You do spend quite a bit less time in lower gears by using WOT and short shifting. The trick is to shift soon but only when your engine produces enough torque not to bog down.

full article is here:
"Better driving to save fuel" (http://www.thestar.com/NASApp/cs/ContentServer?pagename=thestar/Layout/Article_Type1&c=Article&cid=1146693012850&call_pageid=968867497088&col=969048871196)

FWIW, i've heard BMW mentioned in the context of WOT/short-shifting before, but didn't pursue it then.

so i headed over to road and track to search for the info. didn't find the bmw reference, but coincidentally, they're also running a feature on the index page called "Your Mileage May Differ - An enthusiast's guide to saving fuel" in which the author writes:

Remember Coach Grimbly's dictum about "driving with an egg under your foot"? Forget it. The most efficient way to reach cruising speed is wide-open-throttle (WOT) short-shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gears, when throttling and pumping losses are their greatest.

WOT/short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it's certainly fun â€” and efficient as well â€” to accelerate briskly through the lower gears to whatever the ambient speed happens to be.

full r&t article (http://www.roadandtrack.com/article.asp?section_id=20&article_id=3424)

have a read. both of these articles make the 20% WOT claim. they also make other claims & suggestions that may help you form an opinion of the respective authors' knowledge on the topic.

hmmm... that elusive bmw study... anyone know anything about it?

philmcneal

05-07-2006, 02:59 AM

hm metro i once read that was thinking make sense... but my consumption sure doesn't tell me so... WOT at rpms lower than 2000 just promotes lugging even further and those pumping losses won't make up for the insane amount of gas you used to get there.

<<However, it's possible IMO that you more than make
up in pumping losses for what you lose in running rich
(this is why turbochargers work AFAICT - they scavenge
energy on the back end to push air into the motor, so
it doesn't have to work to suck air in).>>>

I seem to recall reading that pumping losses under
cruise conditions (5-8% throttle) are about 8%, and my
educated guess is that your driving technique is
costing you about 20% while accelerating.
I'd like to stress that is is easy to prove...Harbor
freight will sell you a digital voltmeter for 4-8$.Run
a long wire through your window and under the hood to
the 02 signal return wire and ground the other lead,
put the meter on the dash and watch while you drive.
If you tell me the year, make, model and engine size
of your car I'd be happy to look up youre schematic
and determine which wire on the 02 the tap in to.
Smog laws dont mandate limits on full throttle
emissions, so they are generally mapped pig rich when
the map sensor (or MAF)sees very low vacuum (or very
high airflow) and the TPS shows over 3.8 volts (more
than 3/4 throttle)

<<But even if that's the case, it makes sense to
accelerate as hard as you can without causing the ECM
to go full rich... >>

Not necessarily.
That used to be true with pre-computer controlled
carburetors. At higher throttle openings, more air
came through the venturi's which atomized the fuel
much better and was way more effecient.
Modern cars have the benefit of both very lean
mixtures
at part throttle and egr. The egr is open the most at
about 15% thottle, which is light acceleration. A big
infux of egr reduces power, which means that the
throttle has to open a little more; net result is
reduced pumping losses.
I'd bet you $2 that your mileage would be at least 10%
better if you accelerated slowly, keeping the egr open
as high as possible (also easily monitored with a
vacuum gauge on the dash tee'd into the egr vacuum
hose and a long supply hose)

HTH

something interesting at maxmpg yahoo forums.

Seroiusly though, we need a throttle that can be programmed for, "hey i want the best acceleration to fuel efficency ratio i don't give a flying rats *** how slow it is, i should be able to MASH down the throttle and my settings will be retained." No need of this "focusing on my foot" bs, no wonder people can't hypermile! They get fed up lol.

At least one company is doing it, "Subaru SI drive (different settings for the electronic throttle position)."

MetroMPG

05-16-2006, 09:04 PM

a link to this research paper was posted at teamswift. it addresses a lot of efficiency issues, including how to optimize acceleration:

http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/final_report.htm

about 1/4 of the way down, see "Factors Affecting Engine Efficiency".

it recommends high load/low RPM acceleration. not WOT, but significant pedal (roughly 60% of engine load).

yet more evidence added on the "brisk acceleration/short shifting" pile.

mikefxu

05-17-2006, 05:54 PM

I have been doing hard acceleration up to 3000rpm and then shifting into the next gear and going through all the gears up to 3000rpm unless I need to put it in 5th to stay at speed. I tried the grandma driving way and it was a pain and didn't notice much improvement in mpg but since I have been doing the quick acceleration till 3000rpm I have gotten noticebly better mpg. It's pretty easy for me to know when 3000rpm comes since I don't have a cat or resonator my exhaust buzzes right before 3000rpm and I know its time to shift.

MetroMPG

05-18-2006, 08:36 AM

phil knox over at maxmpg has the BMW report, and he said he'd try to dig it up. i'll post back here as well if he does.

MetroMPG

05-18-2006, 02:04 PM

I tried the grandma driving way and it was a pain and didn't notice much improvement in mpg but since I have been doing the quick acceleration till 3000rpm I have gotten noticebly better mpg.

this is completely non-scientific: but today i did a school run to pick up my nephew and used a moderate amount of pedal, keeping the revs under 3000.

i managed to pull an 88.1 mpg (US) on a cold start (75F ish ambient, dry roads) for the round-trip, all city / suburban driving. plus i screwed up a couple of times - accelerated into situations too quickly and had to brake more than usual... duh.

i'm reluctant to draw any conclusions, except to say that 88.1 is okay in my books. whether it would have been higher or lower with my typical glacial acceleration technique, only a proper test could say. it certainly didn't seem to be a massive penalty, though.

zpiloto

05-18-2006, 02:05 PM

I'll throw this out. I have an automatic. I did runs over a 1 mile course with different accelerations rates up to 55 MPH then set the cruise control until hitting the finish line. I did 3 runs a piece in the same direction. I tried WTO, 80% Load on the scangauge, 60% load, and a combination of WTO to 35 then 60% load to 55. The weather was 90 with calm winds.

WTO 24.3 24.7 24.5 AVG 24.5
80% 23.2 23.5 23.7 AVG 23.5
60% 24.2 25.0 24.3 AVG 24.5
WTO-60% 25.1 24.6 24.5 AVG 24.7

Looking at this, which granted will have a lot of errors in it just because it impossible to control the varibles on the open road, the AVG were very close. I think you can do what every traffic will allow and not hurt FE to much.

MetroMPG

05-18-2006, 02:11 PM

interesting.

a key difference: the automatic won't permit you to short shift - it shifts based on load. (though it looks like you tried to compensate for this in the last run with the WOT/35% mix)

the results with a manual transmission may be different.

tomauto

05-18-2006, 02:42 PM

So I dont have to drive like a grandma, this is great. I guess the downside to this might be a little more braking (if you get a red light or hit traffic) and harsher ride for the passengers with the short shifting.

MetroMPG

05-18-2006, 02:55 PM

i'm not going to draw any conclusions yet.

need... more... data...

and be careful: despite this thread title, i still seriously doubt that WOT the way to go - you may run into open loop, retarded timing, increased friction...

about 50-60% load seems to be the target for a 2-valve engine:

http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/image/Final_29.gif

(source: http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/final_report.htm#_Toc1018)

the right axis is Brake Specific Fuel Consumption (BSFC) - is the measurement of fuel required to produce a given amount of power.

note the lowest BSFC is your goal: you want to produce the maximum power with the least amount of fuel. it definitely does not appear to be at either highly throttled engine conditions, or WOT. actually, it looks like higher loads are less penalized than very low loads.

eek. is my glacial acceleration technique melting?

http://en.wikipedia.org/wiki/BSFC

philmcneal

05-19-2006, 04:07 AM

yeah remember my baby easy acceleration? Now this is what i do

easy baby accel to 2000 rpms

shift into 2nd gear

very little throttle at 1000 rpms... 10%

1500 rpms increase throttle a bit 20%

2000 rpms increase throttle a bit more 30%

2500 rpms increase throttle to almost 40%?

3000 rpms shift! (lol ^ pretty much my OWN vtec pff who needs it)

whatever from there, that gets my car going really fast. Any slower and yeah i'm taking way too long to get to get to 40 km/h

still managing to get 50 mpg segments without easy baby. I think i'm going to drop it since I don't know... impatient and it hurts the foot to exert pressure from my right leg.

MetroMPG

05-22-2006, 10:01 AM

another auto publication weighs in in favour of high load/low RPM acceleration for increased efficiency.

(thanks to babelfish for the awesome german-to-english translation!)

With full power accelerate sounds widersinning, functions however with modern a splashes (does not apply to mechanism and Diesel): With full power to approximately 2000 revolutions accelerate saves in extreme cases five to ten per cent. Reason: With easy acceleration the butterfly valve stands in the Ansaugtrakt, consumption-increasing eddies develops unfavorably, with full power however stands the butterfly valve beautifully slim in the Ansaugtrakt. Tip for mechanism and Diesel: little gas give, with Turbos full load pressure avoid.
source: AutoBild.de (http://babelfish.altavista.com/babelfish/trurl_pagecontent?lp=de_en&trurl=http%3a%2f%2fwww.autobild.de%2ftest%2fneuwag en%2fartikel.php%3fartikel_id%3d11378%26artikel_se ite%3d3%26A_SESS%3d3ae2fd50edaba0a055e9ea09c2538cb d)

philmcneal

05-22-2006, 08:59 PM

another auto publication weighs in in favour of high load/low RPM acceleration for increased efficiency.

(thanks to babelfish for the awesome german-to-english translation!)

source: AutoBild.de (http://babelfish.altavista.com/babelfish/trurl_pagecontent?lp=de_en&trurl=http%3a%2f%2fwww.autobild.de%2ftest%2fneuwag en%2fartikel.php%3fartikel_id%3d11378%26artikel_se ite%3d3%26A_SESS%3d3ae2fd50edaba0a055e9ea09c2538cb d)
going to have to try WOT to 2000 rpms.

i like some of the tips.

MetroMPG

05-22-2006, 09:26 PM

I don't think WOT is the way, Phil. Something between WOT and glacial appears to be the answer.

(SVOboy, if you're following this thread, what do you think about re-titling it so as not to be misleading?)

SVOboy

05-22-2006, 09:30 PM

Haha, of course I'm watching, sitting in my hell of automaticness (this weekend my life will change...). You're so smart, Darin. You could;ve just changed it yourself, :p

JanGeo

05-23-2006, 06:59 AM

Brisk accelerations and getting out of the lower gears as quickly as possible is the key - the longer you stay in a low gear the more fuel you waste making the engine turn over more for distance traveled. However you don't want to be WOT because of the engine injection, timing etc changes that occure plus one or two poor spark fires and the gas is lost. If shifting properly you don't have time to get the throttle wide open before the next gear - smooth throttle changes to better control (reduce) accelerator pumping effect. It seems from my SG readings that any acceleration in lower gears yields lower MPG readings than simular acceleration in 5th i.e. at 20mpg I get better MPG with the same acceleration (with more throttle) in 5th than I do in any other lower gear with less throttle.

Compaq888

05-23-2006, 07:40 AM

JanGeo is right the longer you stay in lower gears the more fuel you waste. I once drove home at like 3am and I was going so slow I mainly was in 1st and second. I burned up about 1.5 gallons. I could of just taken the freeway and only burned half a gallon. Cars aren't very efficient in loser gears. You could be driving 1300rpm in lower gears on the street or drive 2200 rpm on the freeway. You would save more gas on the freeway because the gears that are below 1.000 are saving you more gas. They spin faster than the engine, while the lower gears spin more than the engine.

Think of it this way. You get on your bike and you put it in 1st and you are pedaling like a crazy maniac going 5mph. The when you put it in 6th gear you're pedaling harder but you are going 30mph. You spend more energy pedaling 1st because you have to spin more times for the wheel to move one complete turn. In 6th you maybe spin half a turn to get a full wheel turn. You save your energy and you don't look like a bumbling idiot like in 1st gear.

MetroMPG

06-09-2006, 01:18 PM

FYI, for what it's worth (not much), I used moderate load, low RPM acceleration for the majority of my most recent 75 MPG tank. (Metro95 - I need another acronym, please!)

That proves nothing about the effectiveness of the technique because it still needs a proper test. Maybe my tank would have been higher with glacial acceleration; maybe it would have been lower. All it tells me is it probably doesn't have a large negative impact.

Also, Phil on the MaxMPG list has confirmed he has a copy of the BMW acceleration study and he says it does NOT advocate WOT. He's going to get me a scan or a digital pic. I'll post it when it arrives.

philmcneal

06-10-2006, 12:07 AM

Also, Phil on the MaxMPG list has confirmed he has a copy of the BMW acceleration study and he says it does NOT advocate WOT. He's going to get me a scan or a digital pic. I'll post it when it arrives.

awesome! i knew it sounded fishy when WOT = better mileage. Thats totally opposite logic.

MetroMPG

07-28-2006, 06:04 PM

Phil Knox was kind enough to share the text of the BMW reference he remembered from Popular Science magazine, July 1981:

Good news for jackrabbits

Sudden starts waste gas, right? Wrong, according to a BMW study which shows that three-quarter-throttle acceleration is more efficient than a slow, gradual speedup. Reason: Your engine runs more efficiently at a heavy throttle position, and makes the most of the gas it burns. At about 2,000 RPM, you should shift gears and accelerate the same way, getting into high gear as quickly as possible. (You can accomplish the same thing with an automatic-transmission car by accelerating quickly, then letting up on the pedal to allow the transmission to shift.) Then let your engine loaf along at a steady speed near the 2,000-rpm level.

The problem with slow acceleration is twofold: At slow speeds, the engine is doing little more than idling: and it must run longer to get from point A to point B.

This advice runs counter to the readings you get from those computerized mpg meters, which will indicate poor fuel economy during fast acceleration ("Mpg Meter," Aug. '80). The reason for this is that most meters measure engine vacuum level, not fuel consumption. Their readings are accurate at cruising speeds but can be misleading during acceleration from a stop.

I think the explanation there is a little weak, but suspect that's the fault of the Pop Sci writer, not BMW.

Now that I have a bit more info, I'll track down the original study to see the methodology & details.

SVOboy

07-28-2006, 06:07 PM

Indeed, it makes sense, it does, but I think there is a point where the length between stops balances out a bit. I mean, if you're stopping every half mile and you jackrabbit to speed you're going to lose all that to braking almost immediately. Since the benefit is in elongated coasting time and not gas used during acceleration you need to be able to use that extra distance you've gained yourself effectively to cancel out the loss from the added throttle.

MetroMPG

07-28-2006, 07:53 PM

Agreed on your caveat. Regardless of rate of acceleration, you need to avoid turning fuel into brake dust.

MetroMPG

08-07-2006, 08:45 PM

Bad news on finding the original BMW reference:

Thank you for your email.

I spoke to several colleagues who are working in the department which was responsible for this kind of study, but obviously the original does not exist anymore. Since the premises on engine development changed drastically since the oil crisis - and this was a long time ago - it was probably not deemed necessary to file every single study.

That's sad, but there's nothing else we can do. Also the study would be of not much help today, because it was based on the technologies of this time, which - especially regarding high-tech engine - have changed a lot.

We regret that we cannot give you another answer.

Yours sincerely,
BMW Mobile Tradition
Group Archives

JanGeo

08-08-2006, 05:26 AM

looking at the graph above it seems 20-30% power at around 2000 rpm is ideal for max efficiency - interesting because that is about 40mph in 5th gear on my xB where I get sometimes 50mpg . . . willl have to check the LOD reading at that speed.

omgwtfbyobbq

08-08-2006, 07:21 AM

Word on the street is that during WOT the ECU switches to open loop and a richer mixture to maximize power. Not sure if it's true, but it's what I've always 100% 4real heard. Now the funny thing is, the best FE during acceleration will probably be right before you trigger open loop, so we have to ask, from a stop, how much throttle before open loop in each gear? It's probably different for each car depending on how that manufacturer wants the car to drive, i.e. what's throttle tip-in, what are the gear ratios at the gear we're in, what does the torque curve look like, etc... The only problem is, aside from testing, how can we determine this?

JanGeo

08-08-2006, 07:23 AM

ScanGauge tells you if you are open loop or not as well as LOD (% of pwer at current RPM)

omgwtfbyobbq

08-08-2006, 07:46 AM

Ooooo... That's pimp. You could build some little clicker that you can feel when approaching open loop via the throttle, according to the SG. Someone test a buncha cars, then patent it and make trillions, or a little less. :D

MetroMPG

08-08-2006, 08:11 AM

SVOboy

08-08-2006, 09:35 AM

I have no idea about testing, but just a thought: I was beating on my mom's car yesterday and I floored up to 40 in a few seconds and then coasted for ~1 mile to my stop, I wonder.

Gary Palmer

08-08-2006, 10:30 AM

Ok, I got a thought on this. If you have a way to monitor the Oxygen Sensor, with a meter, gauge, light's or something, then I would think the most efficient you could get would be if you accelerated as fast as the ecu would allow the firmware to stay in closed loop mode. In closed loop it's monitoring the Oxygen Sensor and the sensor voltage should be oscillating as the controller keep's the fuel adjusted, to swing the sensor voltage up and down. If you accelerate faster than that, you put the system into open loop mode and it's just going to read the air fuel ratio's off of the map's, irrespective of the sensor level's. Whatcha think?

zpiloto

08-08-2006, 10:57 AM

Speaking of testing, what would be a valid way to test low load vs high load (low RPM) acceleration?

I would think you'd also want to find best acceleration to cruising speed, and also best acceleration to codfishing.
Pick a preset distance say between 1/2-1 mile and accelerate to cruise speed from a stop and at the end point hit the scan gauge and see what the amount is.

Although mine is an automatic I found that to accelerate to cruise speed the amount of fuel difference is very small but the best for me was to accelerate at WOT to 35 MPH and then reduce to 60% load for the rest of the acceleration. Matching what the folks at BMW came up with. Now if traffic would only allow that.:D

MetroMPG

08-08-2006, 08:20 PM

Gary: you may be on to something. As someone else pointed out recently, the ScanGauge will tell you when you're in closed/open loop. So that will help find thresholds.

zpiloto: I forgot you had done this already. Just a comment: the BMW folks did not advocate WOT; they suggested 3/4 throttle (to avoid open loop, I presume). I also suspect you're right - that for accelerating up to cruising speed, the method doesn't make a large difference.

Also, if I recall, someone at CleanMPG has done this (acceleration over a fixed distance), but it was for a CVT equipped car (possibly an Escape Hybrid - I forget). I've yet to see if anyone has done it for a manual car. I do believe the transmission type plays a role in which technique is best.

I also think Ben's onto something - the gains may be in using the right acceleration technique when followed immediately by a Codfish.

Brick - are you reading this? Wasn't that one of the first topics you discussed at CMPG? Did you ever do the testing?

SVOboy

09-03-2006, 11:33 PM

Did a little testing, oh noes: http://crxmpg.com/accelmpg.html

krousdb

09-04-2006, 06:10 AM

I'm thinking that what you referred to as "Jack Rabbit" starts are more like what I would call moderate acceleration. Jack Rabbit usually refers to full throttle. It would be a good data point to the the same but with WOT.

ZugyNA

09-04-2006, 07:00 AM

Speaking of testing, what would be a valid way to test low load vs high load (low RPM) acceleration?

You could install an adjustable chain on your throttle pivot/cable? You will need a very fine adjustment though...I used heavy copper wire for infinite adjustments.

For the low throttle test maybe at the throttle opening required to maintain 55 mph...or lower? Shift at 1500 RPM?

For the high throttle test...set the chain at about 1/3 throttle or maybe 1/2? Shift at a the same RPM?

You only need to watch the tach.

Need to be careful about where you are testing and that you don't get a stuck throttle.

JanGeo

09-04-2006, 07:12 AM

I think if you just did a couple of 0 to 40/50/60 runs with the scangauge resetting it between runs you could tell right away if brisk or slow acceleration would be better - just make sure you do the slow runs first and then repeat for the fast runs going the same distance - just reaching terminal speed sooner for the brisk runs.

MetroMPG

09-04-2006, 07:45 AM

Interesting! He goes out with a bang. PS Nice to see the mid 60's coming from your car. (Did you have license plates on during the shenanigans?)

I think if you just did a couple of 0 to 40/50/60 runs with the scangauge resetting it between runs you could tell right away if brisk or slow acceleration would be better

I think that would be misleading. A simple 0-to-x comparison, resetting as you reached the target speed would only tell you that brisk acceleration uses more fuel.

The big question being addressed is whether the total fuel economy along a given distance is different depending on rate of acceleration in the beginning portion of that distance.

I'm not surprised that the difference is small. It's what zpiloto discovered too, if I remember right.

When I did the 133 mpg round trip using pulse and glide, I used a fairly aggressive amount of throttle (I'm guessing 60% - enough that I could hear "induction noise") up to about 2600 RPM. Which proves nothing without a comparison, except that 133 is attainable with moderate load/low RPM .acceleration.

SVOboy

09-04-2006, 04:38 PM

The reason I called it jack rabbit is cuz it was so much faster than normal, I was trying to compare the tortoise and the hare, after all. I should put a note in there about WOT when I get on campus though, la la la.

JanGeo

09-05-2006, 03:11 AM

I think that would be misleading. A simple 0-to-x comparison, resetting as you reached the target speed would only tell you that brisk acceleration uses more fuel.

That's not what I said, you would go the same distance say .5 miles at a terminal speed of 40/50/60 accelerating slowly and briskly once each run. The point is to see if slow or quick acceleration takes more fuel to get up to speed - it is NOT clear that faster acceleration take more fuel than slow to get up to speed but you do have to keep the test distance constant. Time to go that distance will also vary during the test but that is not being considered. What we may find is that the sooner you get into top gear the better or the slower you burn the fuel the better.

MetroMPG

09-05-2006, 12:16 PM

That's not what I said, you would go the same distance

Whoops - right you are. Hothead that I am, replied too soon & missed that. Sorry!

JanGeo

09-05-2006, 01:31 PM

It is a subtle difference - and even going the same distance it will be possible to throw off the results because of the time involved if you get up to speed faster then the average speed would be higher of course that IS the point of the testing. What yeilds the lowest fuel used - what we want to test is how much it takes to get up to speed.

omgwtfbyobbq

09-06-2006, 01:38 AM

The relationship depends on how much pumping/friction losses are wrt to your engine. If you know what engine's in your car, find the BSFC map and you'll have all you need to know. Unless you have a drive by wire system... And in that case, you are teh scr3w3d. Anyway BSFC maps show you just how efficiently your engine is operating at a certain load/rpm. For instance, when I'm cruising at 55mph in my (moms) 92 V6/auto Camry (dotted lines I think) , my BSFC is greater than 500g/kwh because I'm using very little hp/torque compared to what the engine is capable of. Larger displacement engines have to pump more air at a given power/torque level, and suffer from a decrease in efficiency as a result.

http://www.v6performance.net/gallery/data/500/70SAE950805_Fig11.gif

Specifically, my engine is operating at ~16% efficiency when cruising at ~55mph. So even though at near full throttle, from ~1.7-3k rpm, my engine is running at ~32% efficiency, most of the time it's running at, or around, or less than half of that. Ideally I can probably get around 60mpg since I get ~30+mpg@55mph, but due to CA drivers and auto transmission, I probably won't see that. Anyway, pulsing and gliding, codfishing, whatever you want to call minimizing pumping losses, works. The driver can maximize how much it works, and determine what their optimum FE is for a given P&G cycle/conditions provided they have the BSFC maps for their vehicle, or spend enough time experimenting. :thumbup:

Compaq888

10-08-2006, 06:51 PM

so rh77 do you really ring out your motor to 3000rpm????

Because that might be the problem why your fuel economy reached it's limit.

rh77

10-08-2006, 07:29 PM

so rh77 do you really ring out your motor to 3000rpm????

Because that might be the problem why your fuel economy reached it's limit.

Yup. I get it up to speed, and practice the usual driving techniques where the real FE lives at cruise. As you know, the automatic makes it tough with the kickdown at optimum throttle input.

(Redline is 6750 or thereabouts). So in first gear sometimes I shift from 1st to 2nd which holds the gear. I can give it 50-60% throttle from there on and shift into 3rd. Then the tricky part: getting it to stay in 3rd and give a dose of throttle; then at 3000 I lift and left the car shift until 4th gear.

If you ask a 100 hypermilers you'll get different answers: accelerate as slow as possible, or get to the point and start to build the FE. I'm not saying to floor-it as that would cause open loop, but try to get up to 3-grand to see if it works out.

Strangely enough, if you take the same car and conditions:

Accelerate slowly: the Scangauge will show an avg of 17 mpg for say 1 minute. Then at minute 2, you're into 40 mpg territory.

Accelerate briskly: the scanguage will show 9 mpg for 0.5 minutes. Then at 30 seconds, you're at 40 mpg at each interval up to 2 minutes. Average FE over 2 minutes in each scenario:

Math:

Slow Accel: ((17+40)/2 = 28.5 mpg avg. at minute 2
Fast Accel: (9+60)/2 = 34.5 mpg avg. at minute 2 (60 is 1.5*40 for the 90 seconds of 40 mpg).

As you can see, it's worth getting up to speed instead of spending a lot of time at ineffecient acceleration. It works for me in the TSX and in the 'Teg. I'd say that I'm doing the best I can now with both cars (TSX still breaking in and we keep getting better mileage at each tank -- the 'Teg is up to Hypermiler due to a recent stent on the long Interstates of Oklahoma and Kansas. The mirrors were folding in for less Cd. and I ended up in the 40's at cruise with constant throttle on hills.

RH77

Compaq888

10-08-2006, 08:36 PM

that's weird. I'll have to test some of those theories when I get a SG2.

LxMike

10-09-2006, 05:13 PM

Yup. I get it up to speed, and practice the usual driving techniques where the real FE lives at cruise. As you know, the automatic makes it tough with the kickdown at optimum throttle input.

(Redline is 6750 or thereabouts). So in first gear sometimes I shift from 1st to 2nd which holds the gear. I can give it 50-60% throttle from there on and shift into 3rd. Then the tricky part: getting it to stay in 3rd and give a dose of throttle; then at 3000 I lift and left the car shift until 4th gear.

If you ask a 100 hypermilers you'll get different answers: accelerate as slow as possible, or get to the point and start to build the FE. I'm not saying to floor-it as that would cause open loop, but try to get up to 3-grand to see if it works out.

Strangely enough, if you take the same car and conditions:

Accelerate slowly: the Scangauge will show an avg of 17 mpg for say 1 minute. Then at minute 2, you're into 40 mpg territory.

Accelerate briskly: the scanguage will show 9 mpg for 0.5 minutes. Then at 30 seconds, you're at 40 mpg at each interval up to 2 minutes. Average FE over 2 minutes in each scenario:

Math:

Slow Accel: ((17+40)/2 = 28.5 mpg avg. at minute 2
Fast Accel: (9+60)/2 = 34.5 mpg avg. at minute 2 (60 is 1.5*40 for the 90 seconds of 40 mpg).

As you can see, it's worth getting up to speed instead of spending a lot of time at ineffecient acceleration. It works for me in the TSX and in the 'Teg. I'd say that I'm doing the best I can now with both cars (TSX still breaking in and we keep getting better mileage at each tank -- the 'Teg is up to Hypermiler due to a recent stent on the long Interstates of Oklahoma and Kansas. The mirrors were folding in for less Cd. and I ended up in the 40's at cruise with constant throttle on hills.

RH77

Thats something i've been wondering with having an automatic and having it doing the shifting. i'm real easy on the pedal and s.g shows max rpm's never go more than 2300. i'm wondering about getting up to speed a bit quicker?? my cars auto tranny the t.c will lock up at 42 mph. when it does rpm's drop 300-400 and mileage jumps from low 30's to consistent mid 40's and nearly 50 at times. I think this is my next mileage exp to work on.

rh77

10-09-2006, 06:05 PM

Thats something i've been wondering with having an automatic and having it doing the shifting. i'm real easy on the pedal and s.g shows max rpm's never go more than 2300. i'm wondering about getting up to speed a bit quicker?? my cars auto tranny the t.c will lock up at 42 mph. when it does rpm's drop 300-400 and mileage jumps from low 30's to consistent mid 40's and nearly 50 at times. I think this is my next mileage exp to work on.

I'm thinking that the quicker you get to TC lockup, the better. Having a small 4-cyl. like myself, 3000 RPM seems to be the ceiling, then I lift the throttle, let it shift, and repeat. More testing would need to be required, but the Math adds up.

RH77

Brock

10-16-2006, 09:42 PM

Here is a test I ran a while back

Ok, this proves I am crazy.

I found a stretch of highway that has a 2.1 mile run between turn offs. I ran in each direction twice at the same acceleration and got up to and stayed at 65. When I went to turn off (2.0 miles), I took the reading off scangauge right before I released the throttle. So basically these are 4 runs at each acceleration rate. None of the individual runs ever varied in to the range of the faster or slower run, with amazing close numbers for each run not varying by more then 1 mpg. I have to say I was surprised at the results. I thought the slower acceleration might be a bit better, but thought it would be very close, almost not noticeable. I could have accelerated even slower, but I was turning on to a 2 lane divided highway and wanted to do it as slowly as I could while being safe. Take it for what it’s worth.

slow run up to 65mph
37.5 mpg

normal or medium run to 65mph
33.9 mpg

fast, or as fast as I could shift and go
29.1 mpg
And no matter how long you drive at your set speed it will never even out for the trip with a quick acceleration. Yes, if you look at MPG/time your better off getting up to speed quickly, but for MPG/distance overall the slower you accelerate the better your mpg, at least with my car.

MetroMPG

10-17-2006, 07:23 AM

Crazy, eh? Welcome to the crazy party!

Very interesting results.

I don't suppose you happen to have a Brake Specific Fuel Consumption map for your car, do you? For acceleration, I'd expect the best FE technique may differ between throttled gasoline engines and throttle-less diesels.

JanGeo

10-17-2006, 07:42 AM

WOT - lets not forget that low intake vacuum is what is desired to reduce pumping losses and that can occur at low RPM with very little throttle opening so there is no need to floor the gas pedal and make the throttle sensor go crazy . . . just lugging the engine will result in low intake vacuum.

Also everyone should do an RPM to GPH use plot on their engines with NO LOAD to get an idea of how much fuel is used just to spin the engine. You should see substantial fuel use above 2-3k RPM depending upon how tight your engine is. My xB starts at .1gph at idle and jumps to 1.0gph at 4000RPM and above - I think it is still a little tight at 8500 miles.

Brock

10-17-2006, 09:49 AM

I am not sure what the "Brake Specific Fuel Consumption map" is but I think I have seen something with that name over on the TDI forums, if Lug Nut see this he will know.

omgwtfbyobbq

10-17-2006, 10:08 AM

This?
http://home.earthlink.net/~rps1976/Images/Diesel/TDI%20Fuel%20Consumption%20Map.jpeg
It pretty much sums up why diesels get so much better mileage than gassers. Even though peak efficiency is about the same when taking into account the difference in BTU per gallon, they have better BSFC ovals in terms of low load driving.

MetroMPG

10-17-2006, 10:14 AM

BSFC plots engine load (throttle input) against fuel consumption, and it's a way to see at what point an engine is producing the most power for the least amount of fuel consumed.

It's a useful thing to know when considering acceleration tactics, but not particularly useful once at cruise (when you want the lowest overall fuel consumption rate, regardless of whether it's the most efficient in terms of power produced per unit of fuel burned).

omgwtfbyobbq

10-17-2006, 10:19 AM

It can be, if the driver decides to pulse and glide, depending on curcumstances. But than again, I guess that's not cruising, even though the pulse and glide driver can have the same average speed and the one cruising, as well as better mileage.

MetroMPG

10-17-2006, 10:30 AM

I'd make the same distinction: P&G isn't cruising, even though it can have the same avg speed.

I tend not to P&G on (infrequent) freeway trips. I save it for shorter, lower average speed rural highway driving. I try do it in moderation because it's harder on the vehicle (and the driver) than cruising.

Compaq888

10-18-2006, 12:14 AM

Well I tried the Moderate accelaration technique. Shifted into 2nd at 10mph, 3rd at 15mph, into 4th at 20mph, into 5th at 30mph.

Barely did any P&G because my speedo would plummet like a fat man off a roof.(Yes I know objects of different weight fall at the same rate.)

Whenever I saw a yellow or red I coasted in gear.

Did a trip of about 25 miles. ALL CITY 42.9MPG <---Scangauge data
Stopped at about 50-60% of the lights. Which means it's real life data, that's how it usually is in the daytime.

My best tank thus far is 42.00mpg and that's mixed driving(freeway and streets) and that's with really slow accelaration.

onegammyleg

10-18-2006, 04:54 AM

my cars auto tranny the t.c will lock up at 42 mph. when it does rpm's drop 300-400 and mileage jumps from low 30's to consistent mid 40's and nearly 50 at times. I think this is my next mileage exp to work on.

You might want to investigate the way your TC systems locks up.
Perhaps you can force an early lock up manually with just a switch and some extra wires.

molecule

10-18-2006, 05:22 AM

whats the relationship between BSFC and Torque...???
i think in this lies the total answer per engine
because transmissions are torque multipliers...
and clearly any engines power output is going to be related to its fuel consuption fairly directly...
your best pull on a dynamometer is most accurately interpreted in 3rd gear...
because its a 1:1 ratio or the closest to it...and then considering the final drive gearing...
i haven't mastered this math...but i'm sure its what needs to be looked at...

cross reference your dyno plot with a bsfc plot and i think you could find your 'target average rpm' fairly easily...
leading you finally to the best speed to maintain in 5th gear...etc
and i wont be surprised if your average rpm for acceleration should be up over 3k on many engines...

personally, when i accelerate, i can feel the engine produce near its maximum acceleration when pressing the pedal further induces no gain...
its somewhere close to 33% and i carry the lower gears to higher rpm...4k-5k...
because they multiply the torque more...so use it while you can get it...

JanGeo

10-18-2006, 05:54 AM

Barely did any P&G because my speedo would plummet like a fat man off a roof.(Yes I know objects of different weight fall at the same rate.)

In air objects of different densities fall at different rates i.e. a feather falls slower than a paper clip although they weight about the same weight. So your small frontal area heavy car does better than a lighter one on a downhill or coasting on a level surface. This helps you with the pulse glide because with higher weight you can run the engine under load longer and then coast longer. Your best savings for coasting is going to be on slight downhills. Now if you are not rolling freely then you need to check your wheel drag. The greatest savings while coasting is at higher speeds if you keep the engine running - with the SG you can now see at what minimum coasting speed your mileage drops below "in gear" mileage.

rh77

10-18-2006, 04:37 PM

If I know I'm going to be cruising under load, I get into top gear +TC, with 45% throttle, lifting to shift at 3000 RPM, get up to the desired speed +5 MPH, and let off the gas to drive with load on hills, etc. It gets to the optimum FE quicker, instead of lagging in low 20's on a slow accel.

Also, my TC is super sensitive in cold weather and requires something to kick in. Prob. coolant temp/trans. load. I've looked into a switch, but I believe I have a TCM.

RH77
Referring to the 'Teg

molecule

10-18-2006, 06:43 PM

i forgot to link the calculator i host...
yeah i stole it...but only because i lost the original link to the site...
credits of creator are still on the page

you can open in text editor to change default values...
or just enter them in the page each time
differential gear is the final drive...and then just choose a gear
http://users.adelphia.net/~digitalcongo/tirecalc.htm

BEN_EJ8

10-18-2006, 10:16 PM

I A-B-A tested this, and it looks like my civic has a powerful lust for gasoline when I lower the shift point and give it 40-50% throttle. Ive been driving like an old lady for a while, accelerating so slow I get passed within 5 seconds of the light turning green sometimes, averaging 37 mpg while shifting at 2500. Then, after reading this thread, I tried giving what I think is a little less than half throttle while accelerating from a stop, and shifting at only 2200. Not good at all; for 3 weeks I got 33 mpg on every fillup; atleast its consistent :thumbdown:

Now this past week I went back to my old acceleration, and since its been raining every single day for 2 weeks I have been coasting less, but still managed to get my best mpg to date, a whopping 6 mpg more than lowering my shiftpoint/raising throttle open a little. Im mad that its been raining every day; I couldve very easily surpassed my goal, but instead Im stuck less than 1 mpg away with winter weather setting in any day now. :(

JanGeo

10-19-2006, 04:21 AM

BSFC - ok how do you figure out where you are operating on the graph . . . by the fuel consumption in gph? We don't have torque measuring instruments in our cars.

omgwtfbyobbq

10-19-2006, 05:22 AM

BSFC - ok how do you figure out where you are operating on the graph . . . by the fuel consumption in gph? We don't have torque measuring instruments in our cars.

Sure we do, our right feet, er, foot? At least on FI cars that use a TB. When a drive by wire system is in use even throttle is out of the driver's hands, er, feet. So in that case it would be hard to tell w/o a tps reading. But as long as I have a tach in a TB/FI car, I know that when I floor it, it's sucking in as much air as possible, and the torque at some rpm is proportional to how much air I let in the engine via the gas pedal.

Something I've noticed when driving cars with drive by wire is that throttle tip in seems excessive. The same amount of gas pedal movement produces much more torque in a drive by wire car compared to a TB car, so I think that quite a bit of ECU programming has gone into minimizing pumping losses this way by almost always accelerating in nice BSFC regions, so that manufacturers can further increase the mpg the average driver gets.

Back to TB/FI, we can assume that minimum BSFC happens where the sum of friction and pumping losses is minimized, so at some lower rpm for friction, higher throttle area fr pumping losses.

JanGeo

10-19-2006, 08:10 AM

Yeah but the graph curve for a certain BSFC is only available at a certain range of RPM you have to really know the fuel consumption - torque is all relative to gearing and incline and full throttle is not where you want to be in most cases according to the graphs. I guess I will go by the acceleration vs pedal input and stay in the area where the acceleration is the best for the least pedal used - the crisp zone - before I enter the bog zone when I give it too much pedal.

omgwtfbyobbq

10-19-2006, 09:30 AM

The thing with full throttle is that even though the mixture's richened on purpose, it's still better than minimal throttle by a long shot. For instance in the first graph I posted, at full throttle fuel consumption only becomes worse than 1/3rd throttle at 4k rpm. A confound is that going at full throttle for any extended period of time will have you going faster than at minimal throttle so unless you have exactly the same average speed, you're wasting energy more efficiently. ; ) At exactly the same average speed, 1/2-full throttle should have the engine operating about twice as efficeintly when accelerating, which is why drive by wire cars are so peppy, they are almost always going at some significant portion of throttle to mimize BSFC.Like you said, going by acceleration compared to pedal on a drive by wire system is best since hopefully, the ECU has already picked a good throttle/rpm range for efficiency so you can just concentrate on driving slowly.

JanGeo

10-19-2006, 04:07 PM

I have a feeling with my VVT-i engine with the variable intake valve timing they already compensate for the pumping losses at low throttle by closing the intake valve after BTC allowing some of the pumping losses to be recovered on the compression stroke by closing the intake on the upstroke of the compression stroke allowing the vacuum to pull the piston up. Will have to find the graph for my engine a Scion xB.

omgwtfbyobbq

10-19-2006, 04:39 PM

I think what you're refering to is the atkinson cycle (http://en.wikipedia.org/wiki/Atkinson_cycle), which initially draws in more air then it needs, then leaves the intake valve open after the throttle plate has closed in order to have some of the air pushed back in the manifold and reduce the difference in pressure/pumping losses.

iirc a vvti engine doesn't stay open to change the amount of air/pressure after the intake valve has closed, which is what's responsible for a significant portion of low load pumping losses. it just opens earlier, almost during the exhaust stroke, to let more air in at a lower rpm as well as allow for some measure of internal egr. it allows for nicer low end torque/power w/o sacrificing high end torque/power. Here's (http://www.youtube.com/watch?v=9A6S1NUjg_A) an animation of the process.

It's definitely better than a normal engine because it virtually eliminates an entire section of low load operation when accelerating by pulling in more air than the normal engine can, but it's still not as good as the atkinson cycle which can minimize pumping losses at any engine load/speed, like cruising on the freeway.

Throttle Position During Acceleration and its effect on FE [ Archive] - GasSavers.org - Helping You Save at the Pump