Throttle Position During Acceleration and its effect on FE

[SVOboy]

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. 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]

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.

[GasSavers_DaX]

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]

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

[rh77]

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]

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]

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]

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.

[GasSavers_brick]

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]

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."