Acceleration mini-experiment

[ELF]

Most of these tests are with MT? I think auto would fare a little different........ might have to do some testing with the sable when I have time.

[VetteOwner]

ye aive noticed this too. at least with my truck. if i shift at 2000-2500rpm i get around 25mpg. i tried shifting less than 2K which didnt last long cuz truck bogged down easily. but i saw a big loss in my mpg (22mpg) im gonna try 3K and see what happens.

[GasSavers_Brock]

That’s weird, when I tested the slow acceleration proved better every time. I can't remember, I posted them here somewhere, but if the rapid acceleration it was like 15 mpg up to 65mph then cruising at 65 it was55 mpg. On the slowest acceleration it was like 30 mpg up to 65. The faster acceleration just could never catch up to the slow one in overall mpg’s for the run.

[VetteOwner]

keep in mind mine is a truck...with a underpowered 4banger. higher rpm's might be easier on the engine or the PCM might sense that the truck is under a heavy load and try to dump more fuel in to compensate...

[MetroMPG]

Brock, could that be a gas/diesel difference?

With a diesel's much flatter torque curve (and presumably far "broader" BSFC map), and lack of throttling losses (one of the things the relatively inefficient gassers overcome with this driving style that get them into a friendlier BSFC zone), I'd expect to see little or no gain driving an oil burner like this.

Can you comment on the benefit (or lack thereof) of doing P&G in a diesel? I suspect if there is any, it's much less pronounced than in a gasoline car.

[caprice]

I read somewhere that if you go WOT in low RPM, it is more efficient. Not too low. 1500 rpm i think. It would be less drag on the intake stroke. This would be dependant on the ECM programming ("your results may vary"), because if the fuel mixture is enrichened, then the benefit is less.

[caprice]

Remember in high school physics class, there is a measurment for the rate of acceleration? Miles per hour squared, i think.

Heck with the physic caluclations I used to do in school, and a scanguage, you could do graphs of MPG vs Trottle position vs RPM. Then M/H^2 vs Fuel.

Also you could do a quarter mile fuel usage testing... instead of measuring speed, you measure fuel consumption. At the "traps" be going 45 MPH every time. Test from (WOT to 45mph then cruise) to (take the whole quarter mile to accelerate to 45 MPH.) Graph it.

Just wanted to throw some idea out there. My manual transsion car is out of commision this week, I'm fixing a power steering leak. And I don't have a scanguage yet.

[Bill in Houston]

Originally Posted by caprice

...because if the fuel mixture is enrichened, then the benefit is less....

Mmm-hmm. I think that this is the key. Accelerating as quickly as you can w/o making the ECU put you in open-loop or in a richened state.

Originally Posted by caprice

...Also you could do a quarter mile fuel usage testing... instead of measuring speed, you measure fuel consumption. At the "traps" be going 45 MPH every time. Test from (WOT to 45mph then cruise) to (take the whole quarter mile to accelerate to 45 MPH.) Graph it.

Ya, that would be perrrrfect.

[kps]

Originally Posted by SVOboy

http://crxmpg.com/accelmpg.html

Here's mine, *shrug*

Yes, this test, via the Throttle Position During Acceleration and its effect on FE thread, is what made me want to try this myself. In my case, though, I wanted to try it without involving any hypermiling techniques.

Originally Posted by Bill in Houston

Mmm-hmm. I think that this is the key. Accelerating as quickly as you can w/o making the ECU put you in open-loop or in a richened state.

I suspect you are right; the car does go open loop under full throttle, but acceleration (by 'feel', anyway) does not change very much between heavy and full throttle. Given that, and that I expected from others' tests that rapid acceleration to be more efficient, I decided to use WOT to (presumably) put rapid acceleration in a worse light, i.e. to see whether it's more efficient even if the driver is not careful with the throttle.

I think the next test I'd like to do is between WOT and rapid closed-loop acceleration, provided I can manage the latter reasonably reliably, e.g. with a mechanical stop under the accelerator.

[GasSavers_Brock]

Metro yes this could very well be the difference between diesel and gas. And yes I tried two weeks of trips home running P&G every other time and got within 1% of my non-P&G trips. So I can only assume P&G doesn't add much for diesel's. Of course when warm I idle at about .25L or 8oz per hour.