Throttle Position During Acceleration and its effect on FE - Gas Savers

SVOboy · 09-05-2005, 10:50 AM

Quote:

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

Quote:

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.

Quote:

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.

Quote:

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.

Quote:

I feel there will be a point of diminishing returns on lean burn, but every application is different. Mine does not like lean ratios. It’s happier in mid 14’s, but it still makes 35/gal on half city half hwy – 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 I’m sorry, there is no way in hell full throttle is more efficient than part throttle. I’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

Quote:

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

Quote:

Originally Posted by philmcneal

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

Quote:

Originally Posted by MetroMPG

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

Quote:

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

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."

rh77 · 05-04-2006, 10:06 AM

Quote:

Originally Posted by MetroMPG

Quote:

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

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

Quote:

Originally Posted by rh77

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".

Quote:

-- 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

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.

For the record, my normal driving is 1st and 2nd up to 2000rpm and then 5th for the other 97% or the drive. I normally cruise in the 800-2200 range in 5th gear, the median range being 1100-1400. I climb a few moderate hills in 5th. For the remaining hills I use 4th withi one exception where 3rd is required.

philmcneal · 05-04-2006, 04:31 PM

Quote:

Originally Posted by krousdb

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

Quote:

Originally Posted by philmcneal

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

Quote:

Originally Posted by philmcneal

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):

Quote:

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"

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:

Quote:

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 — and efficient as well — to accelerate briskly through the lower gears to whatever the ambient speed happens to be.

full r&t article

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?