Throttle Position During Acceleration and its effect on FE

[rh77]

Originally Posted by MetroMPG

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."

The manual should say something like "Don't make jack-rabbit starts and stops, but do not accelerate too slowly" -- basically you need to get into that higher gear as quickly and efficiently as possible. With the auto-trans, I generally give it 20% on the throttle (without A/C) and climb to the needed speed. Immediately when it shifts, the MPGs jump up by double. It's a technique, for sure -- which I haven't mastered.

Oh...and I had my Triple-Shot Espresso in my Almond Mochacinno this morning, so I'm up to normal operating specifications ;-)

[MetroMPG]

Originally Posted by rh77

The manual should say something like "Don't make jack-rabbit starts and stops, but do not accelerate too slowly"

i've often seen the jack-rabbit warning, but never anything about accelerating "too slowly".

-- basically you need to get into that higher gear as quickly and efficiently as possible.

i don't think you can generalize on this point. depends on what's coming up next in your driving (e.g. imminent stop/slow down). also, there are likely differences in what technique is best depending on manual or auto.

[krousdb]

I did some very limited testing with the Del Sol. I started one of my morning commutes using aggressive acceleration to get up to speed and then normal 5th gear driving from there. When I say aggressive, i mean about 1/2 throttle, not WOT but much more than I normally use. Anyway, by the time I got to my 2nd milestone, my FE was so much below my normal targets that I stopped the test and went back to normal driving technique. It wasn't worth killing the tank FE any further. I wish I had the data to present, but my fading memory says I was 10-20% below normal by the second milestone.

For the record, my normal driving is 1st and 2nd up to 2000rpm and then 5th for the other 97% or the drive. I normally cruise in the 800-2200 range in 5th gear, the median range being 1100-1400. I climb a few moderate hills in 5th. For the remaining hills I use 4th withi one exception where 3rd is required.

[philmcneal]

Originally Posted by krousdb

I did some very limited testing with the Del Sol. I started one of my morning commutes using aggressive acceleration to get up to speed and then normal 5th gear driving from there. When I say aggressive, i mean about 1/2 throttle, not WOT but much more than I normally use. Anyway, by the time I got to my 2nd milestone, my FE was so much below my normal targets that I stopped the test and went back to normal driving technique. It wasn't worth killing the tank FE any further. I wish I had the data to present, but my fading memory says I was 10-20% below normal by the second milestone.

agreed, I quote from my post from cleanmpg:

__________________________________________
I think i cracked it to why Wayne perfers super slow acceleration. The high mpg rates (35 mpg +) never bought down my average as it would do if I were to follow the manual's way to acccelerate (5-15 mpg). Here's what I discovered:

1st gear littlest amount of throttle possible (20-25 mpg rates) up to 2000 rpms

Shift (now wayne perfers the fast shift so that he doesn't lose velocity, since I'm a noob I shift slow and wait for the clutch to be done its buisness before attempting to accelerate since I can't afford a clutch job)

2nd gear should be down to 1000 rpms again, now extremely little throttle (30 -35 mpg rates) and your speed should climb slowly, we talking about like 1 kilometers per hour per second! but your patience will be rewarded as your instantenous mpg goes up along with it! climbing by 2 points as you get up to speed oh here comes 2000 rpms again!

Shift (i sometimes clutch in, go into neutral and wait for the revs to drop before sliding it into 3rd to make the sync, although its much harder to do when your revs are so low and the difference is not that great)

3rd gear revs should drop to 1500 rpms, now the littest amount of throttle possible (first trying just to maintain rpms, then slowly rising up slow) and then your speed will increase by 1 kph again (those using miles it could be harder to judge since your numbers mean a lot!) and these mpg rates will be around 35 - 45 mpg rates and then another battle to 2000 rpms!

Shift (ok from 3rd to 4th for some odd reason, is the easist gear out of them all. The motion of just "Down" and the difference in rpms is so little that this shift is just the easist to master, I don't know I guess you can say this shift is the fastest shift I'll do without losing speed like my first 3.)

4th gear now this is where it gets exciting! back down to 1500 rpms, and climbing slowly by 1 kph again. But rates are at 45-60 mpg almost and even when climbing a small incline or some sort, I don't even have to downshift (unless i'm down to 1000 again) because apparently the small pull is still good enough, although with the mpg meter minus 5-10 depending on the incline and then going back up as the road steadies itself, but still very good! Even when reaching as high as 2000 rpms you can start to see the max mpg i can get 60 + and then starts to drop again as you climb over 2000 rpms... kinda cool.

Shift (now from 4th to 5th is a little odd, the drop is quite big and I'm glad it is because I have a decent overdrive to boot! When above 2000 rpms (highway reasons) when shifting I do the sliding in the neutral trick and wait for revs to drop before shoving it into 5th with no risistance (i hate that feeling, why should a gear reisist to be selected? because its not ready yet!).


5th overdrive (drops to 1500 rpms): Depending on the revs, my mpgs can be as high as 100 when giving the littlist throttle possible, or as much as 50 mpg if I'm climbing a small incline. What I like about 5th is when you climb inclines with 5th, your speed bleeds a lot less as opposed to in 4th, this definately tells me there's less friction to battle at 5th for sure! Just the gearing for the overdrive is so deep is that we have to make sure never to lug it (under 40 mpg instanteous) but using 5th to MAINTAIN or BLEED off speed is okay and should be done if you want to save some brakes!


So lession of the day is, what the book recommends is the best ACCELERATION TO EFFICENCY RATIO and what WE want is HIGH FUEL EFFICENCY WITH NO MENTION TO TIME WHATsoEVER. Since I drive in the heart of the city and red lights are a commonblode to me (I don't think I've timed all the green lights yet... maybe one day) so I think I'll be practicing more of this type of acceleration just because it does not dent my average ever and I'll never see anything below 40 mpg!!!!! AVERAGE ;D

but hey this is just a civic

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[MetroMPG]

Originally Posted by philmcneal

your speed should climb slowly, we talking about like 1 kilometers per hour per second!

are you some kind of crazy person? you're a speed freak compared to my rates of acceleration!

seriously, good info phil. thanks for cross-posting that.

[philmcneal]

and the stats bleh i pretty much memorized it: conversion is through my head so correct me if i'm wrong

2300 rpms MAX (oh yeah ~~)
4.9 LPK or 47 MPG
64 Km/h MAX or 40 mph
35 km/h AVG or 25 mph
8.7 KM drive (5.3 miles)
12 minute drive
88 max coolant temp (C) (max is 90)
2 stop signs
9 turns
9 lights
gone through 5 green lights
4 1st gear starting out
4 FAS ( bump started before my momentum dropped below 30 km/h then idled for less than 10 seconds before 1st gear start)
.4 liters consumed (.1 gallons)

on my way home wasn't as pretty, since i dediced instead of FASing, i'm going to give little throttle for 5th gear instead (at least i'm saving gas legally)

5.8 LPK (40 mpg)
2400 RPMS MAX
64 km/h max
40 km/h average
9.3 km drive (5.5 miles)
15 minute drive
90 max coolant temp
1 stop signs
5 turns
11 lights
2 minute construction work idling wait
7 1st gear starts (ouch... everyone went fast and made the green and i slowed poked to stop at it
0 FAS :O
.6 liters consumed (.2 gallons)

bleh blah shifting sucks. I wish there was an abusable CVT in which I can FAS and then regen energy if I needed to stop, one can dream. Also with no FAS my battery voltage stayed at a high 13.5 volts than its ususal 12.8 volts... but since I leave the car outside (too lazy to call the house to open the garage, and FAS into my driveway is too bumpy) i'm sure it will stablelize itself back into the 12 volt area as tempeartures go down and up again.


edit: i forgot to add and i thought it was equally as important. As you shift to the next gear and slow accelerate towards 2000 rpms (1 kph per second) I notice as the MAP starts out around 6.5 to 7 but as you increase the speed that number drops in .3 increments allowing your FE to jump up. As more speed is built upon, that same pressure on the throttle magically goes lower and lower as maybe the ECU finally realized that "hey I want to really conserve fuel man! Light off the pressure!" and slowly as you gain speed that exactly what happens! when I reached in MAPS of under 5.5 then looking at the tach i'm at 2000 rpms and then the MAP will increase over 6 again (higher fuel consumption)!

Shift!

[GasSavers_DaX]

Originally Posted by philmcneal

1 kilometers per hour per second!

haha, what a weird unit of acceleration!

[GasSavers_Randy]

I think there's something special about the Insight that keeps WOT from ruining mileage. Nearly all cars run rich mixtures for extra power (max power is slightly richer than stoichiometric, max mileage slightly less). Back in the days of carbs, low vacuum would open the 'power valve', which was like increasing the main jet size. Computers do the same thing, but without the cool name.

Supposedly most cars run most efficiently just below this enrichment point... maybe 80% throttle.

[rh77]

So, that's 0.62137 MPH per second?

I think I do about 2 mph per second, or good grief: 3.24 Km/H/Sec!

[MetroMPG]

the toronto star newspaper ran a "how to drive efficiently" article today that recommended WOT & short-shifting.

i wrote to the author for more info on the source of the "studies" he mentions in support of WOT, and got this reply (within an hour, which was a surprise):

BMW pioneered the WOT method back in the '80s and found it gave better fuel economy. It first appeared in a Road & Track article at about the same time. You can access older Road & Track articles through their website I believe. BMW would probably allow the public access to that information as well. The idea behind it is internal combustion engines are very inefficient at part throttle settings and most efficient at wide open throttle. You do spend quite a bit less time in lower gears by using WOT and short shifting. The trick is to shift soon but only when your engine produces enough torque not to bog down.

full article is here:
"Better driving to save fuel"


FWIW, i've heard BMW mentioned in the context of WOT/short-shifting before, but didn't pursue it then.

so i headed over to road and track to search for the info. didn't find the bmw reference, but coincidentally, they're also running a feature on the index page called "Your Mileage May Differ - An enthusiast's guide to saving fuel" in which the author writes:

Remember Coach Grimbly's dictum about "driving with an egg under your foot"? Forget it. The most efficient way to reach cruising speed is wide-open-throttle (WOT) short-shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gears, when throttling and pumping losses are their greatest.

WOT/short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it's certainly fun — and efficient as well — to accelerate briskly through the lower gears to whatever the ambient speed happens to be.

full r&t article

have a read. both of these articles make the 20% WOT claim. they also make other claims & suggestions that may help you form an opinion of the respective authors' knowledge on the topic.

hmmm... that elusive bmw study... anyone know anything about it?