Throttle Position During Acceleration and its effect on FE

[philmcneal]

hm metro i once read that was thinking make sense... but my consumption sure doesn't tell me so... WOT at rpms lower than 2000 just promotes lugging even further and those pumping losses won't make up for the insane amount of gas you used to get there.

<<However, it's possible IMO that you more than make
up in pumping losses for what you lose in running rich
(this is why turbochargers work AFAICT - they scavenge
energy on the back end to push air into the motor, so
it doesn't have to work to suck air in).>>>

I seem to recall reading that pumping losses under
cruise conditions (5-8% throttle) are about 8%, and my
educated guess is that your driving technique is
costing you about 20% while accelerating.
I'd like to stress that is is easy to prove...Harbor
freight will sell you a digital voltmeter for 4-8$.Run
a long wire through your window and under the hood to
the 02 signal return wire and ground the other lead,
put the meter on the dash and watch while you drive.
If you tell me the year, make, model and engine size
of your car I'd be happy to look up youre schematic
and determine which wire on the 02 the tap in to.
Smog laws dont mandate limits on full throttle
emissions, so they are generally mapped pig rich when
the map sensor (or MAF)sees very low vacuum (or very
high airflow) and the TPS shows over 3.8 volts (more
than 3/4 throttle)

<<But even if that's the case, it makes sense to
accelerate as hard as you can without causing the ECM
to go full rich... >>

Not necessarily.
That used to be true with pre-computer controlled
carburetors. At higher throttle openings, more air
came through the venturi's which atomized the fuel
much better and was way more effecient.
Modern cars have the benefit of both very lean
mixtures
at part throttle and egr. The egr is open the most at
about 15% thottle, which is light acceleration. A big
infux of egr reduces power, which means that the
throttle has to open a little more; net result is
reduced pumping losses.
I'd bet you $2 that your mileage would be at least 10%
better if you accelerated slowly, keeping the egr open
as high as possible (also easily monitored with a
vacuum gauge on the dash tee'd into the egr vacuum
hose and a long supply hose)

HTH

something interesting at maxmpg yahoo forums.

Seroiusly though, we need a throttle that can be programmed for, "hey i want the best acceleration to fuel efficency ratio i don't give a flying rats *** how slow it is, i should be able to MASH down the throttle and my settings will be retained." No need of this "focusing on my foot" bs, no wonder people can't hypermile! They get fed up lol.

At least one company is doing it, "Subaru SI drive (different settings for the electronic throttle position)."

[MetroMPG]

a link to this research paper was posted at teamswift. it addresses a lot of efficiency issues, including how to optimize acceleration:

http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/final_report.htm

about 1/4 of the way down, see "Factors Affecting Engine Efficiency".

it recommends high load/low RPM acceleration. not WOT, but significant pedal (roughly 60% of engine load).

yet more evidence added on the "brisk acceleration/short shifting" pile.

[mikefxu]

I have been doing hard acceleration up to 3000rpm and then shifting into the next gear and going through all the gears up to 3000rpm unless I need to put it in 5th to stay at speed. I tried the grandma driving way and it was a pain and didn't notice much improvement in mpg but since I have been doing the quick acceleration till 3000rpm I have gotten noticebly better mpg. It's pretty easy for me to know when 3000rpm comes since I don't have a cat or resonator my exhaust buzzes right before 3000rpm and I know its time to shift.

[MetroMPG]

phil knox over at maxmpg has the BMW report, and he said he'd try to dig it up. i'll post back here as well if he does.

[MetroMPG]

Originally Posted by mikefxu

I tried the grandma driving way and it was a pain and didn't notice much improvement in mpg but since I have been doing the quick acceleration till 3000rpm I have gotten noticebly better mpg.

this is completely non-scientific: but today i did a school run to pick up my nephew and used a moderate amount of pedal, keeping the revs under 3000.

i managed to pull an 88.1 mpg (US) on a cold start (75F ish ambient, dry roads) for the round-trip, all city / suburban driving. plus i screwed up a couple of times - accelerated into situations too quickly and had to brake more than usual... duh.

i'm reluctant to draw any conclusions, except to say that 88.1 is okay in my books. whether it would have been higher or lower with my typical glacial acceleration technique, only a proper test could say. it certainly didn't seem to be a massive penalty, though.

[zpiloto]

I'll throw this out. I have an automatic. I did runs over a 1 mile course with different accelerations rates up to 55 MPH then set the cruise control until hitting the finish line. I did 3 runs a piece in the same direction. I tried WTO, 80% Load on the scangauge, 60% load, and a combination of WTO to 35 then 60% load to 55. The weather was 90 with calm winds.

WTO 24.3 24.7 24.5 AVG 24.5
80% 23.2 23.5 23.7 AVG 23.5
60% 24.2 25.0 24.3 AVG 24.5
WTO-60% 25.1 24.6 24.5 AVG 24.7

Looking at this, which granted will have a lot of errors in it just because it impossible to control the varibles on the open road, the AVG were very close. I think you can do what every traffic will allow and not hurt FE to much.

[MetroMPG]

interesting.

a key difference: the automatic won't permit you to short shift - it shifts based on load. (though it looks like you tried to compensate for this in the last run with the WOT/35% mix)

the results with a manual transmission may be different.

[tomauto]

So I dont have to drive like a grandma, this is great. I guess the downside to this might be a little more braking (if you get a red light or hit traffic) and harsher ride for the passengers with the short shifting.

[MetroMPG]

i'm not going to draw any conclusions yet.

need... more... data...

and be careful: despite this thread title, i still seriously doubt that WOT the way to go - you may run into open loop, retarded timing, increased friction...

about 50-60% load seems to be the target for a 2-valve engine:



(source: http://www.tc.gc.ca/programs/environ...t.htm#_Toc1018)

the right axis is Brake Specific Fuel Consumption (BSFC) - is the measurement of fuel required to produce a given amount of power.

note the lowest BSFC is your goal: you want to produce the maximum power with the least amount of fuel. it definitely does not appear to be at either highly throttled engine conditions, or WOT. actually, it looks like higher loads are less penalized than very low loads.

eek. is my glacial acceleration technique melting?

http://en.wikipedia.org/wiki/BSFC

[philmcneal]

yeah remember my baby easy acceleration? Now this is what i do

easy baby accel to 2000 rpms

shift into 2nd gear

very little throttle at 1000 rpms... 10%

1500 rpms increase throttle a bit 20%

2000 rpms increase throttle a bit more 30%

2500 rpms increase throttle to almost 40%?

3000 rpms shift! (lol ^ pretty much my OWN vtec pff who needs it)


whatever from there, that gets my car going really fast. Any slower and yeah i'm taking way too long to get to get to 40 km/h

still managing to get 50 mpg segments without easy baby. I think i'm going to drop it since I don't know... impatient and it hurts the foot to exert pressure from my right leg.