Ideal rate of acceleration?
 

What is the ideal rate of acceleration, in regards to fuel economy?
I'm looking for statistics.

Thanks.

crxMPG - Gas mileage never looked so good » Acceleration and Fuel Economy Tested

But then there's so much variation from car to car and all

Thanks man, this is perfect.

You want to accelerate at whatever power output is best BSFC for your engine. Typically this is much faster acceleration than people think would give them the best FE. I call it "moderate" acceleration.

I have read that BMW instructs drivers to accelerate at 75% engine load and shift when the engine's mean piston speed reaches 1200-1500 feet per minute. Mean piston speed is a function of engine stroke and RPM.

Vp=RPM*S/6

Vp= mean piston speed
RPM= engine speed
S= engine stroke length, inches

This keeps you in closed-loop operation (for EFI) at high volumetric efficiency with low frictional horsepower loss for as short a time as possible before you can achieve steady-state cruise and/or EOC. It is what I like to say is accelerating "smartly."

MechEngVT: That's kind of funny... when I first started to try hypermiling, I tried to get my automatic to downshift below 2000 RPM (by letting up on the gas a bit), but it was kinda hard to do without lurching in my Protege, not to mention holding up people behind me in congested traffic. So I've gone to using 2000 to 2500 RPM as my downshift target. When I solve your equation for the 1200 to 1500 fps range I get .... 1988 to 2495 fps. Now I don't feel quite as guilty about letting the rev get up to 2400 to 2500. ;-)

Interest info MechEngVT. Where did you find this info?

I am trying to figure out the best way also. I have read easy acceleration. How easy is easy. The link above seems to suggest that going out fast is better than going out easy. I have ready to accelerate as fast as possible without going open loop. I have read that accelerating with a high LOD is the best way. The RPM stuff doesn't mean much to me since I drive an automatic and have little control over what RPMs the car shifts at. I have no clue what BSFC is.
Can someone post in easy to follow instructions the best way to accelerate for the best fuel efficiency. Pretend that I am kind of slow (um...yeah...pretend :P ).

Thanks,
RJ

This is a very difficult problem. The data on the linked site above is convincing for the vehicle and conditions tested, but EOC isn't a viable option for me in my LR3.

Why is it difficult? You'd think that it would be a matter of running at the most fuel efficient portion of the engine map (for the poster above, BSFC is "brake specific fuel consumption," see here for a pretty good article) up to the intended speed, presumably that which yields best fuel economy.

But the wild card is the fact that, when accelerating, you're using fuel both to overcome external resistance (drag, rolling resistance) and to add kinetic energy. It's easy to show that the more slowly you accelerate, the greater distance covered in the process of adding a fixed amount of kinetic energy (the kinetic energy of the vehicle at the selected final speed). So, there are three considerations: slowly adding kinetic energy, spending as much time as possible at the most efficient speed, and operating in the most efficient portion of the engine map.

I've rigged a "generic" engine map (they all kind of look similar) and used known points for my engine to try to use optimization techniques to find the most efficient acceleration but, mathematically, it's a difficult problem. Especially for an old fart like me (math is a young person's game). But if and when I reach a conclusion, I'll post it.

Man, that's a long post for no particular conclusion, but I did want to point out the kinetic energy aspect, which I don't see anyone considering in discussing this issue.

torque is the work . non-japanese inline four bangers find it naturally.
I made a funny. anybody get it? :D

your foot finds it for your car: the slowest rpm to get what you want. Screaming weirdos enignes don't understand and called it moderate to heavy acceleration...

a big diesel at 40 tons loaded is getting 224 mtpg (mile tons per gallon) all while never seeing much more than 2k rpm. The ultimate workers has no concept of this "perfect throttle".It is never a concern. all else who ask have pansy driveline. "Statistics" you seek will only reveal the most common driveline. Most likely that dumbo inline four cylinder...and those are in the moderate to heavy acceleration to get a thing called torque doing the work...
the concept of hypermiler would not exist if we had real engines.... :turtle:

:confused:

"Glorious sunset of my heart was fading. Soon the super karate monkey death car would park in my space. But Jimmy has fancy plans... and pants to match. The monkey clown horrible karate round and yummy like cute small baby chick would beat the donkey." - Jimmy James

The "best acceleration" is also complicated by real conditions. You only need to accelerate downhill enough to prevent the onset of road rage in people behind you. Going uphill, you just need to punch it. Crawling uphill means staying in low gears for longer. The name of the game is getting into high gears as soon as possible.

I've been accelerating with loads between 70 and 80 and I'm seeing better or rather more efficient use of my MPGs by the time I reach 4th gear. I might have broken 43mpg on my last trip if I wasn't stuck with traffic. Had to settle for 41.

Daox:

As I stated I've read that BMW recommends this, but so far I have yet to find it as a direct source. I have read it from a gentleman who posts on Dodge Truck forums and lists who has spent much time experimenting with fuel efficiency on his truck and researching efficiency and aerodynamics. The feet/minute number is a rule of thumb as far as I know so it may not be optimized for any specific engine design, but all of us here probably lack the means to determine the optimum number.

I find that the 1200 fpm target correlates well with my personal experience. My engine, with a 3.40" stroke, hits 1200 fpm at 2117 RPM. I have gotten my best fuel efficiency lately shifting at 2100. I get my best steady-cruise efficiency at 2100 in 5th (75 mph) with another "island" of efficiency ~1800-1900 in 5th (65 mph) both achieving identical MPGs. If I wound out to 1500 fpm that would put me at 2647 RPM and I know it's not worth my while to drive that fast on the interstates (would have to put me near 95 mph), when accelerating from a stop up a hill I will let it rev to 2500 before shifting and find that not only does it work better in the elevated torque band, it keeps me out of open-loop enrichment under the load of uphill acceleration.

There is a direct correlation between an engine's stroke and the speed at which that engine will naturally produce a torque peak. As noted above the engine's stroke directly correlates an engine's speed to a mean piston velocity. As engines produce more low-speed torque they need to be run slower to maintain efficiency, and as engines produce more high-speed torque then can be run faster and still be efficient. All you folks out there with Honda b16s with a 3.05" stroke should let 'er rev up to 2360 instead of dogging it down below 2000 rpms (Wiki says the D16A3 in a Civic HF has a 3.405" stroke, putting you guys at 2100 rpms like me).

I found this thread via Google, and wish to share my tactics for fuel efficient acceleration. What I've done is through experimentation, found the lowest speeds my car will shift at (2001 Toyota Echo AT: 15km/h, 25km/h, and 46km/h OR 9mph, 16mph, and 29mph) and do some 'upshift coaxing' to get my car to shift at these points.

However, I have found that by doing this over time, shifts seem much rougher than before, especially when doing regular and smooth acceleration. This point was driven home when I had to drive the company van, and couldn't even feel the thing shift unless I accelerated REALLY slowly.

I'm currently trying to accelerate slowly AND smoothly to get it to shift as close to these speeds as possible without coaxing. I'll report back next time I fill up.

This is my suggestion: Drive about a week trying to find when your car shifts. Once you have an idea of where it does, use upshift coaxing to try and get it to shift even earlier. Once you've determined all the slowest speeds your car shifts at, accelerate slowly to get it to shift as close to these points as possible.

Another note: When doing 'smooth and slow acceleration' it may not always be able to recreate the same shift points. If I accelerate VERY slowly, I find the transmission will be struggling to upshift, thus using more fuel probably. You want to accelerate slowly, but you also want it to shift without struggling either. If it is struggling, you need to give it more gas so it can shift. I find with my car it isn't a problem for it to shift into 2nd at 15km/h, but will shift at 30km/h and 50km/h unless I upshift coax, regardless of how slow I accelerate.

UPDATE: Well, my economy dropped significantly by accelerating slowly and smoothly. I went from a solid 35-39MPG down to about 33MPG!!! I guess I was tempted to try this because of my experience driving another vehicle (Toyota Sienna), but if I had spent more time with it I'm sure I would have found its shift points.

Also, try accelerating a different speeds to determine shift points. Sometimes its easier to hear the car shift when giving it more throttle.

heres my method:

i have a slightly louder exhaust (and a decent sized motor), so i can "hear/feel" the motor pretty well. while my truck is an automatic, it has 5 gears that are actually pretty close in ratio (not much rpm drop in between gears).

its kinda hard to explain in words, but i'll try my best. there are 2 main "feelings" i get from my engine.

-when i accelerate really slowly, the engine "feels" like it wants to go faster, but i'm holding it back. makes it stay in lower gears, and the shifts aren't "crisp". it shifts like i get out of bed in the morning; slow, tired, and sluggish. small variations in accelerator pressure don't seem to make any difference (in speed).

-when i give it more (like 3000 rpms+ ), i get excessive noise, the engine "feels" like its doing way too much work for the speed i'm traveling.

so my "sweet spot" is around 2000-2300 rpms. when it shifts, rpms only drop a couple hundred, and are short and crisp. i reach higher gears in moderate time. the engine just "feels" happy. that seems to get me the best mileage.

yeah i know, i haven't updated my fuel log in awhile. i do have it saved (in excel) at home. my "mpg tracking" process is always filling up from almost empty, at the same time of day, at the same gas station. my excel program corrects my mileage from bigger tires automatically.

Yagaa too, me.

it depends...
 

I judge my accel on location and how heavy traffic is...

If the distance between lights is long, I will accel faster to get to a good cruzin' speed. Shorter distance between lights, slower accel. :thumbup:

And as always, I judge all that with how heavy traffic is...

I've found that on a diesel engine accelerating (specifically my 1982 6.2ltr diesel suburban) the slower I accelerate the better my MPG, I can get 20mpg in town with that rig. (which is within 1mpg of the highway)

On gasoline engines it REALLY varies, my buick gets better accelerating slowly, at least when its not bloody cold, my Dodge crew cab is abysmal but generally I need to get out of 1 asap 2nd rapid but controlled, 3rd slow and steady.

What I've found on the Dodge is that the 1st and 2nd gear you start accelerating slow and then ramp up to get out of the gear, basically the lower the RPM the less throttle you use but you have to try to get out of 1st and 2nd relatively quickly or your FE really really sucks. So I am saying your throttle level is variable in any given gear under acceleration.

Good Luck, Its more complicated than many make it seem, and I've found if I just accelerate slowly through all the gears my FE sucks.

I think I have found that my Smart responds to acceleraton at or near minimum BSFC. I found a Mitsubishi publication that was published in conjunction with the release of that engine; it includes a curve of BSFC vs. BMEP at 2000 rpm that seems to show that minimum BSFC at that speed occurs at about 63% of max BMEP.

Now, LOD on the Scangauge is more closely related to IMEP. It doesn't go to zero at zero shaft torque like brake MEP would. I found that at zero torque LOD is about 17 between 2000 and 3000 RPM. So to get a rough target value for LOD under acceleration, I interpolated to find a value that is 63% of the way from 17 to 100 (69).

I try to accelerate at an LOD of around 70-75 whenever possible, shifting at no more than 3000 rpm. I don't have good hard data, but I can tell on the Scangauge that it's better than feather-footing it all the time.

Judging by the BSFC charts I've seen, I think it is best to keep intake manifold vacuum at 5 to 10 inches of mercury and the engine speed in the 2000 to 3000 RPM range on most engines. If slower acceleration is required, then the shifting should be done earlier. Most cars will run smoothly if the transmission is shifted when the engine reaches 2000 RPM. After the shift the engine will probably be running about 1300 RPM. It depends on the transmission gear ratios.

I think it would be a good idea to avoid a heavy load when engine RPM is below 1500 because the oil pressure may be low and a heavy load could increase wear on the connecting rod bearings.

Im not so sure about higher load accelerating in turbo cars such as mine, because Im pretty sure if you give it over a certain amount of throttle it goes to open loop. I know the boost maxes out at any more than half throttle or so above 2000 rpms. 55mph is around 26-2700 rpms in 5th so thats about the only time you have to really worry about that. Its geared pretty low (.8 5th, 3.85 final) so accelerating below 2000 rpms isnt much of a problem.

I often read terms like 75% of throttle, 80% load while talking about the brisk acceleration that is supposed to be most efficient.

Is there a way to figure these in the absence of a scangauge? Any trick with MPGuino to hit the sweet spot?

Any approximations for situations where the stock (and only) instrumentation is a tacho and a speedometer?

well, 75% throttle is exactly that: the throttle is 3/4 of pedal travel to wide open. engine load is a calculation based on several factors, but your ear can probably tell you what the engine is doing. if it sounds like the engine is working hard, your under heavy load. Instrumentation, even a vacuum gauge, makes it the easiest and takes away the guessing.

For my 36 and 37 mpg tanks I was accelerating as slow as possible, for this tank I am getting up to speed more rapidly and thinking it might actually be better to do this. The longer it takes me to get up to speed, the more effort the engine is putting in at low rpms trying to get there. The faster I get to 5'th with out going wide open throttle, the less gas I'm hoping to spend because I'll be at cruising speed at a relatively low rpm sooner.

It makes sense, so I'm hoping it pans out. Maybe I'll go to a 1 gallon fill up to see how it goes? BRB!

Back!... Wow.. uhh I don't know what to say!

I went 55 miles this morning, and I just topped it off.. 1.280 gallons @ 55.2 miles...

43.125 mpg accelerating using 65-70% throttle. Coasting down hills, and 1 turn-off for about 1 mile this morning.

for me as it turns out, using 70% to accel, has resulted in a significant mpg increase apparently.

Best acceleration is 0
 

Best is to find a hill, that for the speed you want to travel:

• has an up gradient that matches the best BSFC of the engine and gearing; and

• has a down gradient that allows you to roll at the speed you want.

Go up the hill. Turn off engine. Roll down the other side at the same speed.
Acceleration = 0
(you may have a little trouble finding the hill, but it must be there somewhere)

I just got my MPGuino in the mail. I won't be hooking it up for a while cause it needs to warm up, and I need to figure out what's wrong with my wheels before I do anything else to the car. Should I get a vaccuum gauge also? Or will a MPGuino tell me what I need to know to optimize acceleration?

Which brings up the question, what numbers would I be looking for on either instrument to know if I'm at optimum acceleration rates?

Using this formula, and my engine stroke length of 3.1", I came up with an ideal range of 2322-2903 RPM... is is really possible that it's that high?

It would explain my dramatically low mileage compared to my fellow Taurus drivers. I try to always keep the engine under 2000. Never over 2500.

Sean, the ECU will come out of the dash and twist your nuts into oblivion if you try to drive at those RPMs. You would have to be going at least 70 to even get into that range, and nearly 90 mph at 3k in 4th gear. So, unless you are locked in third gear (hence the ECU butt-kicking), I doubt you'd see those revs.
You're right to keep the engine around 2k. The little fart of power at 2500 rpm before a shift is useless and puts more wear on our lemur-designed transaxles.
Do you drive in town a lot? I drive 80% country highway and get decent MPG figures from it (when the dang car works right... merf). The Taurus, with its .30 Cd, was built for the highway and can return 30 MPG. However, I've seen lawnmowers get better city mileage...

I do drive a lot in city, kindof... it's not traffic driving. Most roads I take are 55mph with streetlights, but I've done a pure highway tank and came up under 30mpg.

But I mean should I be accelerating with the RPMs at those numbers and then when I hit 45 my car always shifts down to about 1500. after that of course I would stay low RPMs.

I'm just not sure what's the best method of getting to that one major gearshift (I think it's going into 4th).

I agree with your sentiment, PA32R.

The answer to the question is a massive "IT DEPENDS" (TM). And it's why there's no tip for acceleration in the 100+ ecodriving tips list. There is no one size fits all answer.

Also, people tend to fixate on this question, when it could be demonstrated that the way you decelerate has a much larger impact on fuel economy.

Well, after a tank (+partial refill) of accelerating at 2300-2900 RPMs, I've come up with a tank MPG of 22.56, which is better than my average, but not by much.

Must... install... MPGuino... soon...

I'm really gland I found this thread.

I only recently joined Ecomodders after purchasing a gas guzzling small truck for my small business. I bought a ScanGauge and installed it this past Monday. I was surprised to see that my MPG is so low for so long when I accelerate very slowly, and when I accellerate at a more moderate pace my MPG increase much faster.

I am attributing this to the very low gearing a truck has in 1st and 2nd gear which gives you lots of power but not much efficiency. AFAICT from ~100 miles of driving, I seem to get 1-3mpg in 1st and then when it gets into second I get 6-8 mpg. Third gear brings the MPGs into the double digest. The increase in speed probably has something to do with this as well since it increase the miles in "miles per gallon".

I'm glad to see others are having similar results and that I am not crazy. My new strategy will be to accelerate more briskly to get out of 1st and 2nd quickly up to more efficient gears.

I find this very interesting. I have heard that you engine is at its most efficient when it is producing the most torque. The 2.0L New Beetle's peak torque is at 2600 rpm. Using the above equation 1200-1500fpm is roughly at 2000-2600rpm. The actual numbers are 1216, and 1581fps for 2000 and 2600rpm respectively.

i have been watching the Scangauge mpg and gph while accelerating. My theory is, at a steady gph acceleration rate, I let the rpm's increase as long as the mpg keeps increasing every second or so as the Scangauge updates. When the mpg flattens out and no longer increases, I shift to the higher gear.

On a flat road, I accelerate at about 1.5 to 1.8 gph, preferably holding at 1.5 gph if I can. The rpm range of acceleration seems to work best from about 2300 to 2900 with my 1.6l Nissan Versa.

some links for product that may help
 

I have noticed this as well with my jeep. Even though it is an automatic, how far I push the accelerator can vary the RPM's before it shifts. When I accelerate slowly, it will shift anywhere between 2000-2250 RPM. I find that this usually gives me a worse MPG in the long run because the longer the time it takes for the transmission to build up the RPMs, resulting in a long and drawn out rate of consumption of fuel. If I accelerate at a brisk pace, the RPM's will hit between 2500-3000 RPM, which gets me a better MPG in the long term because the time it takes to get up to those speeds is shorter, thus reducing the rate of consumption of fuel.

And that's always the thing about big trucks and SUV's, having terrible consumption in low gear. By having the smaller/shorter gearing, the torque is amazing, but it takes so much energy to get it up to speed. Something that helps though in those low gears is having a 4 WD truck with a limited slip or some type of actuating locker. By having power go to all 4 wheels when accelerating, the energy needed to get the transmission going in low gears is reduced, making accelerations quicker, much cleaner, and helps reduce the fuel consumption from a dead-stop acceleration.

Since I need to replace the front differential on my jeep (thank you lil' sis for engaging the true-locker and taking a turn and blowing the whole thing out), I have been researching a couple replacement options. The two I find best for on-road, and off road if that's your forte, are Auburn Gear brand lockers and Powertrax "no-slip traction system." What's nice about the Auburn Gear ones are they are electronically acuated. When in an off position, the locker acts like a limited slip, but when on acts as a full locker turning both wheels on your axle at the same rate. The Powertrax one is a cheaper alternative that I personally think is brilliant. Inspead of acting like a limited slip, whihc cuts power to the wheel that has grip to the one that has least amount of traction, it will cut power to the wheel with less traction and give it to the wheel that has more traction, thus keeping you moving forward. Rear differentials will end up giving your axle the feel and control like a posi-traction rear end, and the front end diffs will have the same effect.

Links if anybody wants to check these out are:
StylinTrucks.com
Lockers and Other Jeep Parts and Jeep Accessories by 4 Wheel Drive Hardware

The Powertrax locker is made by Richmond Gear. What's cool about this one is they manufacture them for any type of accepting axle for cars, trucks, tractors, and UTV's.

Some trucks (mine for example) are meant to be started in 2nd, except when going up very steep hills or towing/hauling very heavy loads. 1st is really more like "extra low", and 2nd is really 1st.

I'm going to start shifting at 2100rpm now. Their range gave me 2100-2600 (previously shifted normally at 2400-2900).

PS - Sean, I assume you got 2300rpm for 1200fpm and 2900rpm for 1500fpm? The BWM recommendation is to upshift when you reach 1200-1500rpm, and we'd probably work on the low side, so you would probably upshift at 2300rpm.

Another factor is how far apart your gears are. BWM likely has internal consistency, but other makes are probably quite different; this would cause a different upshift recommendation (what, exactly, I don't know).

Edit: To me it felt like I was lugging the engine excessively shifting at 2100rpm keeping LOD at 75-ish. I'm going to try to keep it lower than I have before though, perhaps 2400rpm.