gear choice

[MetroMPG]

<img src="http://old.soliton.net/old/images/tach.jpg" align="right">

Feb 28/06
3:30pm - 4:00pm

car: 1998 pontiac firefly (geo metro); 3-cyl; 1.0L; 5-speed. warmed up with approx 30-40 minutes of mixed city/suburban/exurban driving.

route: 1.8 km / 1.1 mi., slightly rolling - *maybe* 5-10 ft elevation chg over 1.8 km (didn't feel like driving out to my usual test route)

weather:

Air Temperature (ATMP): 18.0 °F / -7.8 C

Wind Direction (WDIR)...WSW ( 240 deg true )
Wind Speed (WSPD).......22 kts (40.7 km/h / 25.3 mph)
Wind Gust (GST).........25 kts (46.3 km/h / 28.8 mph)

http://www.ndbc.noaa.gov/station_page.php?station=supn6

wind note: i probably wasn't subjected to *full* wind conditions shown above; this weather station (roughly 5-10 km from the test route) is fully exposed in open water on the St Lawrence River, and the 1.8 km stretch of road i used has portions which are tree-lined, and other portions which are protected by some land elevation to windward.

results:

test speed 65 km/h / 40.4 mph +-1

all readings taken going in the same direction (s/w).

gear...rpm.....mpg(US) ScanGauge readings (mpg = avg function)

5......2080....55.9
4......2500....47.0
3......3495....41.5
2......5175....25.9

for reference: going in the opposite direction along the same 1.8 km route at the same speed:

5......2080....66.7 (nice wind effect, eh?)

---

notes:

- take this as "snapshot" FYI info only. the mpg precision is NOT good due to the small sample, short course length, uni-directional (non-averaged) runs, and i didn't use cruise control.

- man i *hated* doing that 2nd gear run. my car doesn't have a factory tachometer. without that scangauge (digital tach) i would have sworn i was going to see pistons flying through the hood. aggh! the noise! but i knew ahead of time (from my service manual) that the rev limiter cuts in at 7000 rpm, so i had revs to spare.

- i just don't like revving engines like that. sheesh. the things i do for "science". (okay, i love revving engines on the race track, but i haven't done that for a few years... and never in a 3-cyl! :) )

- i should get bonus points in the gaslog for dragging down this tank's mpg in my quest for knowledge!

[krousdb]

Great job! It confirms what I had been seeing with the SuperMID but your testing is much more scientfic than my casual observations.

Thanks for taking one on the chin for the greater good. But I'm sure with your newfound knowlege that you will make up for it by the end of the tank. ;-)

[MetroMPG]

newfound knowledge? get a taller transmission! :)

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

[krousdb]

newfound knowledge? get a taller transmission! :)

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I would be happy to run those tests if I could find a relatively flat road. Thats a tall order around here.

[diamondlarry]

newfound knowledge? get a taller transmission! :)

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I'll try to remember to check that tomorrow. If I remeber right though, it's somewhere in the 60-70 range. On a recent trip from dropping my daughter off at church, I averaged just over 63 mpg(Scanguage) for the 4& 3/4 mile trip. I was travelling between 35 and 45 most of the time. Since I had the Scanguage in trip mode I'm not sure what the instantaneous mpg was.

[JanGeo]

Boy I gotta wonder about going 40mph in 2nd . . . that is really reving it for sure, I have done it a few times and my Geo sounds pretty good at that rpm.

[diamondlarry]

newfound knowledge? get a taller transmission! :)

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I checked my Scanguage readout at 40 mph in 5th gear and was a bit surprised. It read between 75 and 80 mpg with an occasional spike into the mid 80's. Of course, if I touched the throttle at all, the mpg dropped like a lead baloon back to normal levels.

[philmcneal]

yup 70km/h is indeed the sweet spot to cruise (1800+) rpm's for me in 5th gear. Although at 60km/h it feels that I'm lugging the engine (1500) rpms (or not i dunno) but the car feels more smooth cruising at 2000 in 4th gear though.

Too bad I don't have a scangauge, wonder if I really should cruise at 1500 rpms in 5th... I'll never know i guess!

Besides.. i rather take it out of gear at 70km/h and turn off the engine ;)

[SVOboy]

I've been cruising my mom's camry at 1k rpms, 25 mph in 5th, :)

[JanGeo]

My xB is about 2 to 1 in 5th gear so the lowest it likes is about 1000rpm 20mph and gives about 50-55mpg on a level road but what happens is if I stay at the speed the engine doesn't get lubricated enough. If I throw a rev with the clutch in the mpg goes up to about 66mpg for a little while. Anywhere from 20-30 mph gets high 45-50 MPG going faster 35-40 MPH is good typically in the 42-43 MPG range.

[worthywads]

It varies greatly but at 40 in 5th and little wind I'm between 33-45. I have several stretches on the way to work. I'll run some tests tomorrow.

[worthywads]

I was pleasantly surprised at my short test, each close to a mile. First one netted 52mpg and the second 57mpg.

So my steady state 40mph in 5th is excellent, it the gas it takes to get this mass up to speed that's killing me. I'm probably a lot more sensitive to wind also.

[MetroMPG]

that's impressive for a pickup!

i think you're right about sensitivity to wind and drag - as your speed climbs any higher than 40 mph, watch out.

have you read the story yet about the toyota pickup owner who improved his aerodynamics and boosted his highway fuel economy by almost 30%?

http://www.evworld.com/view.cfm?section=article&storyid=870

[worthywads]

that's impressive for a pickup!

i think you're right about sensitivity to wind and drag - as your speed climbs any higher than 40 mph, watch out.

have you read the story yet about the toyota pickup owner who improved his aerodynamics and boosted his highway fuel economy by almost 30%?

http://www.evworld.com/view.cfm?section=article&storyid=870

Yes I had seen that but thanks for the reminder. Wonder if he's going to market the "topper"? Rear visibility must suffer.

I'm extremely pleased and happy that I chose the 2.7L 2WD. I'll be getting 30+ mpg this summer.

[JanGeo]

I had a little time to test the MPG in a couple of gears at 38mph in 5th 45mpg, 4th 36mpg, 3rd 32mpg on a level road warmed up. Might be more interesting on a down slope in neutral where you maintain a constant speed in neutral coasting and just rev the engine at different RPM - since the net result is to have no change in speed then having it in neutral achieves this - this gives you a no load baseline for engine rpm to fuel economy at a speed that the ScanGauge can operate with.

Next would be in different gears going up a steep long hill to see if light reving or lugging gets better mpg results.

BTW I still see no change in MPG readings in neutral, 5th, 4th, or 3rd going down hill no throttle other than the MPG change due to speed change. I see a reduction in MPG if the engine is reving too high and that threshold rpm needs to be measured more exactly.

[Ryland]

I've been warned by a number of people not to lug 5th gear to much, a mechanic friend of mine said was saying that at least on hondas, and I would suspect other light cars, that 5th gear isn't as heavy, because you would figure most people are going to use it for cruseing at higher speeds, that it's loads are more consistant, I've been paying more attention to my shift light, and noticing that on flat roads it will come on untill I'm in 4th gear going 35mph, engine spinning around 1,200rpm, can do 40mph in 5th, but at least for my car it seems a little slow for that high of gearing.

[krousdb]

I'm in 5th approx 90% of the time, shifting from 2nd to 5th at 20 MPH when not hill climbing. At 1200 I'm only at 32MPH.

[diamondlarry]

I'm in 5th approx 90% of the time, shifting from 2nd to 5th at 20 MPH when not hill climbing. At 1200 I'm only at 32MPH.

You sound like you drive a lot like I do in my Saturn. Your gearing also sounds similar. I'll check tonight and see how fast I'm going at 1200rpm in 5th. Once, when it was late at night and there was no traffic, I got into 5th and took my foot clear off the gas to see how fast I would go in 5th at idle. It was awhile ago but it seems like it was around 10-15. It didn't really shudder too much either. ;-)

[MetroMPG]

I've been warned by a number of people not to lug 5th gear to much ... 5th gear isn't as heavy

i wonder if it would be more of a problem for very torquey engines. a friend of mine lost 5th gear on his mustang 5 liter, and the rebuilder suggested it was from driving in 5th at low rpm/high load.

my car hardly has any torque. if i short shift, i just can't accelerate at all. i tend to go for 5th right around 60 km/h (37mph) when accelerating very gently.

[molecule]

just some food for thought
(the summation of what i have to offer on this topic)
both these engines use the same vtec-e technology

the head castings are very different
the vx is unique...with the motorcyle style intake ports
the 3-stage is the same as all the usdm 1996+ hx/ex/cx (y5/y8/y7)

the 92-95 vx 1.5L gets 48-52 mpg stock hwy
it has a 40mm throttlebody
the final drive is 3.25

the 96+ jdm 3-stage 1.5L engine get 48-52 mpg stock hwy
it has 56mm throttlebody
the final drive is 4.058

[SVOboy]

Where are you getting these numbers from?

[molecule]

http://asia.vtec.net/specs/

i own the 3-stage and i owned the vx for a few years...

[SVOboy]

Interesting then. Would you also propose that a y5 head would yeild similar results then?

[Ryland]

where do you get the ECU for the 3 stage v-tec?
I've thought that getting one would be sweet as they have a higher redline, so that most likely meens better balencing, better bearings, even if I didn't get the matching ECU/wiring.

[SVOboy]

I think since he's using a chipped ecu he must be using a 2 stage ecu then having an rpm activated switch to kick in the 3rd stage.

[molecule]

yeah...i saw a 3-stage ecu on ebay last week for $180...
uh...no thanx...plus i would have to convert to obd2...
and then i cant edit my maps...
i'd rather sacrifice being able to use a scangauge and stay obd1

i converted the distributor connector for obd1...
but later found out any 92-95 NON-VTEC dizzy w/ blue tach wire (i think all of them) is exactly the same as the 96+ dizzy's...

the y5 is a 1.6L engine...it uses more fuel...plain and simple...
all the 96+ heads are identical as far as their casting...
even the 3-stage
the difference is in the cams & rockers only
they all use the same valves...(except the gx propane industrial motor)

i added iab control to my ecu to engage the 3rd stage
but i used the 2nd method which didn't work...
i think i need to use the first method on this page
have yet to try it
if all else fails...then rpm activated switch it will be...
http://www.pgmfi.org/twiki/bin/view/Library/AddIABToP28

[SVOboy]

You could always do the 1 wire vtec like they do with OBD0. Where the a/c clutch is used for the second gear or the automatic transmission thing. I dunno if they've cracked that code for obd1 yet. Mehbe you can turn a shift light or some other signal into the second solenoid signal.