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Old 04-23-2008, 09:39 AM   #1 (permalink)
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Question Power band acceleration

If my vehicle makes its maximum power, at say 3000 rpm, should I run each gear into that rpm range before shifting? This would be assuming a light throttle pressure, not flooring it to get there. Are fewer rpm's better overall or does the efficiency of the engine when making maximum power not matter?

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Old 04-23-2008, 10:11 AM   #2 (permalink)
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Optimal acceleration is had at roughly 80% load. Optimal rpm differs based on engine design. Most cars seem to be most happy between 1500 and 3000 rpm based on BSFC (brake specific fuel consumption) charts that I have seen. In a manual transmission car it is very easy to stay in this range.

If you drive an automatic, you are going to have a hard time keeping your rpm below 3000 and staying around 80% load. In this case you can use a technique called fake or false shifting where you accelerate at the 80% or highest load you can without having the engine downshift. When you hit the top rpm your aiming for, you let off the gas and let it shift to the next gear up. You then reapply the throttle to get 80% or as high a load as you can without making it downshift.
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Old 04-23-2008, 09:01 PM   #3 (permalink)
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awillard69,
As a rough rule the fewer revs the better.
This helps with reducing friction as well as with the volume of air and fuel being pushed through the engine.

The max power measurement is with the throttle at wide open on a dynomometer and has little relevance to the real world where most driving is done at lower throttle openings. It does help to sell cars though which is why car makers keep talking about it.

Efficiency is , as you say , not a priority at this point only getting the maximum power level matters. Engine life is also not a priority either.

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Old 04-24-2008, 09:49 AM   #4 (permalink)
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That's pretty much what I figured. I thought I'd ask. Thanks for the feedback, all.
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Old 04-24-2008, 10:57 PM   #5 (permalink)
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You want low rpms but not so low that you're below the powerband.

Also, don't look at power, look at torque. Peak power tends to be when you're burning gas the fastest. If you can find the torque curve for your engine, you want to accelerate where torque is high, but being at peak isn't neccesary.

As far as % of throttle, I do pretty well around 1/3 to 1/2, but I'm just using a foot gauge and a butt dyno, so I can't tell if that's optimal.
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Old 04-25-2008, 08:35 AM   #6 (permalink)
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And, yes, I meant peak torque, not horsepower. Horsepower is a meaningless value IMO.

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