Throttle Position During Acceleration and its effect on FE

[omgwtfbyobbq]

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.



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.

[Compaq888]

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]

Originally Posted by Compaq888

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]

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

[LxMike]

Originally Posted by rh77

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]

Originally Posted by LxMike

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

[GasSavers_Brock]

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]

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]

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.

[GasSavers_Brock]

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.