Throttle Position During Acceleration and its effect on FE

[MetroMPG]

another auto publication weighs in in favour of high load/low RPM acceleration for increased efficiency.

(thanks to babelfish for the awesome german-to-english translation!)

With full power accelerate sounds widersinning, functions however with modern a splashes (does not apply to mechanism and Diesel): With full power to approximately 2000 revolutions accelerate saves in extreme cases five to ten per cent. Reason: With easy acceleration the butterfly valve stands in the Ansaugtrakt, consumption-increasing eddies develops unfavorably, with full power however stands the butterfly valve beautifully slim in the Ansaugtrakt. Tip for mechanism and Diesel: little gas give, with Turbos full load pressure avoid.

source: AutoBild.de

[philmcneal]

Originally Posted by MetroMPG

another auto publication weighs in in favour of high load/low RPM acceleration for increased efficiency.

(thanks to babelfish for the awesome german-to-english translation!)


source: AutoBild.de

going to have to try WOT to 2000 rpms.

i like some of the tips.

[MetroMPG]

I don't think WOT is the way, Phil. Something between WOT and glacial appears to be the answer.

(SVOboy, if you're following this thread, what do you think about re-titling it so as not to be misleading?)

[SVOboy]

Haha, of course I'm watching, sitting in my hell of automaticness (this weekend my life will change...). You're so smart, Darin. You could;ve just changed it yourself,

[JanGeo]

Brisk accelerations and getting out of the lower gears as quickly as possible is the key - the longer you stay in a low gear the more fuel you waste making the engine turn over more for distance traveled. However you don't want to be WOT because of the engine injection, timing etc changes that occure plus one or two poor spark fires and the gas is lost. If shifting properly you don't have time to get the throttle wide open before the next gear - smooth throttle changes to better control (reduce) accelerator pumping effect. It seems from my SG readings that any acceleration in lower gears yields lower MPG readings than simular acceleration in 5th i.e. at 20mpg I get better MPG with the same acceleration (with more throttle) in 5th than I do in any other lower gear with less throttle.

[Compaq888]

JanGeo is right the longer you stay in lower gears the more fuel you waste. I once drove home at like 3am and I was going so slow I mainly was in 1st and second. I burned up about 1.5 gallons. I could of just taken the freeway and only burned half a gallon. Cars aren't very efficient in loser gears. You could be driving 1300rpm in lower gears on the street or drive 2200 rpm on the freeway. You would save more gas on the freeway because the gears that are below 1.000 are saving you more gas. They spin faster than the engine, while the lower gears spin more than the engine.

Think of it this way. You get on your bike and you put it in 1st and you are pedaling like a crazy maniac going 5mph. The when you put it in 6th gear you're pedaling harder but you are going 30mph. You spend more energy pedaling 1st because you have to spin more times for the wheel to move one complete turn. In 6th you maybe spin half a turn to get a full wheel turn. You save your energy and you don't look like a bumbling idiot like in 1st gear.

[MetroMPG]

FYI, for what it's worth (not much), I used moderate load, low RPM acceleration for the majority of my most recent 75 MPG tank. (Metro95 - I need another acronym, please!)

That proves nothing about the effectiveness of the technique because it still needs a proper test. Maybe my tank would have been higher with glacial acceleration; maybe it would have been lower. All it tells me is it probably doesn't have a large negative impact.

Also, Phil on the MaxMPG list has confirmed he has a copy of the BMW acceleration study and he says it does NOT advocate WOT. He's going to get me a scan or a digital pic. I'll post it when it arrives.

[philmcneal]

Originally Posted by MetroMPG

Also, Phil on the MaxMPG list has confirmed he has a copy of the BMW acceleration study and he says it does NOT advocate WOT. He's going to get me a scan or a digital pic. I'll post it when it arrives.

awesome! i knew it sounded fishy when WOT = better mileage. Thats totally opposite logic.

[MetroMPG]

Phil Knox was kind enough to share the text of the BMW reference he remembered from Popular Science magazine, July 1981:

Good news for jackrabbits

Sudden starts waste gas, right? Wrong, according to a BMW study which shows that three-quarter-throttle acceleration is more efficient than a slow, gradual speedup. Reason: Your engine runs more efficiently at a heavy throttle position, and makes the most of the gas it burns. At about 2,000 RPM, you should shift gears and accelerate the same way, getting into high gear as quickly as possible. (You can accomplish the same thing with an automatic-transmission car by accelerating quickly, then letting up on the pedal to allow the transmission to shift.) Then let your engine loaf along at a steady speed near the 2,000-rpm level.

The problem with slow acceleration is twofold: At slow speeds, the engine is doing little more than idling: and it must run longer to get from point A to point B.

This advice runs counter to the readings you get from those computerized mpg meters, which will indicate poor fuel economy during fast acceleration ("Mpg Meter," Aug. '80). The reason for this is that most meters measure engine vacuum level, not fuel consumption. Their readings are accurate at cruising speeds but can be misleading during acceleration from a stop.

I think the explanation there is a little weak, but suspect that's the fault of the Pop Sci writer, not BMW.

Now that I have a bit more info, I'll track down the original study to see the methodology & details.

[SVOboy]

Indeed, it makes sense, it does, but I think there is a point where the length between stops balances out a bit. I mean, if you're stopping every half mile and you jackrabbit to speed you're going to lose all that to braking almost immediately. Since the benefit is in elongated coasting time and not gas used during acceleration you need to be able to use that extra distance you've gained yourself effectively to cancel out the loss from the added throttle.