increase rpm, accelertion and top speed...

1,545

Asked by Dec 06, 2011 at 08:12 PM

Question type: Maintenance & Repair

- does increasing engine idle also increase acceleration and top speed? i already took care of my rev sync problem, now i just
want a little adjustment...

15 Answers

445

no

1 out of 1 people think this is helpful.

no,to increase top end speed,,1 change the gearing,2 do away with the govener or rev liminter,

2 out of 2 people think this is helpful.
65

Actually about what car are u talking? There's huge difference between street cars and racing cars, different purposes. Acceleration depends about torque and power per weight, aerodynamic of car body, gearing, dimension of wheels+tire, about traction. Top speed depends about power, gearing, wheel+tire size, aerodynamics, stability, downforce. Increasing engine idle cant increase acceleration, nor top speed, but can give a little better respond time, and you can set idle closer to operating torque, power area. Example is F1 engine, idling 4500-5500rpm depends. Increase engine idle at street going car is useless, but at racing car has a purpose.

105

Actually, racing cars don't have higher idle because it makes them faster, they have it because the cams can't handle anything lower.

65

Many racing cars has ''big'' cams and still can idle like street. It's not about cam only (Dodge Charger with 282 still can idle @850-900rpm, raising up to 1100). Air/fuel ratio have more about higher idling than cams. Friends Supra idle at same speed with 236 and with 264 cams but it can rev much higher with 264.

105

It's not as much about cam size, it's about valve overlap, which has both to do with size and angular offset. On F1 cars, the intake and exhaust valves are open at the same time for a while. At low engine speeds, this will cause an extremely dramatic decrease in compression, as most of the intake charge will have simply left through the exhaust valve, so the engine simply won't make enough torque to keep running. At higher engine speeds, the charge has less time to make it's way through the cylinder, meaning less will escape so the compression will be sufficient enough to produce the torque to keep the engine running. Cams are tuned to be ideal for a certain engine speed, so nearly all the exhaust gasses will be pushed out and almost no charge will escape. Also, a higher idle would do nothing for a race car. Think about it, when does a race car ever drop down to its idle? Never during a whole race, except in a pit stop. The driver tries to keep the engine as near the redline as possible, where the powerband is. In older racecars, the driver will use the heel-toe technique to keep the revs up during a downshift, and newer racecars do this automatically. Thus, it does not matter at all to response where the idle is. However, it is preferable to keep an idle lower, as in a pit stop or waiting at the start it will burn a little less gas.

1 out of 1 people think this is helpful.
65

''The driver tries to keep the engine as near the redline as possible, where the powerband is. In older racecars, the driver will use the heel-toe technique to keep the revs up during a downshift, and newer racecars do this automatically.'' --- Rev matching is biggest reason why it rev at downshifts. ''However, it is preferable to keep an idle lower, as in a pit stop or waiting at the start it will burn a little less gas. '' --- race engines are setup to burn rich mixture fuel/air almost all time (high compression, high octane fuel, more power/torque).

1 out of 1 people think this is helpful.
445

This guy has a n/a "140-160 mph" civic with a 1.5 sohc "3 stage vtec" and a close ratio slushbox. Is this even worth discussing?

1 out of 1 people think this is helpful.
105

Your first statement is correct, but has no relevance to the discussion. Your second statement, if correct, would still not relate to the discussion, but it doesn't matter anyways as it is wrong. All engines are set up to run as close to the ideal air/fuel mixture at all times. A little rich is safe, as it will prevent unsafe temperatures, but anything above the ideal will waste power as you have a (nearly) non-compressible liquid not igniting. This means that the engine has to work harder to move that piston up with no additional benefit on ignition. And even if they did run rich, they still want to save gas, and therefor want the idle as low as is healthy for the engine. Do you have any points that actually relate to the discussion? I would appreciate hearing them, but I doubt you do.

65

Every 7 days on track day track behind my hometown, talking with one of the most experienced engineers, one of them working for AMG Division.

105

That's a really good point. Someone on the internet saying they know an engineer for AMG makes them really knowledgeable. I concede. You are inherently more knowledgeable than me.

1,545

we have different ideas. i second that motion.

1,545

its not a slushbox, a gearbox and my car has an engine. it IS worth discussing because that's what Car IQ is for. this is not a site created by and for spoiled sissies with nothing to boast other than them having the bigger engine under the hood. i agree, your car might be faster than mine, but i guaran- damn-tee i got bigger balls...LOL!!!

65

I never said I know more than you, I just learning like everyone. Many things in theory doesn't work in practical. Theory derives from practice. Have a nice day Henry ;)

445

No disrespect intended, I am not a fan of automatic transmissions (doesn't you profile say a/t?) hence: slushbox. 140-160 in a FWD/auto honda without FI? Possible but highly unlikely... I assume these are numbers you saw indicated on your stock 120mph speedo at best. If you have to start a thread asking if increased idle helps acceleration and top speed, you are either: a grossly misinformed novice, riding around with your throttle cable disconnected, trolling, or a dangerous combination of the three. Obviously bringing anatomy into the discussion is on topic, and i regret to inform you, you are most likely mistaken about that too. Sincerely hope your honda brings you great joy, as that is ultimately what carsIQ is about. As a matter of fact, show me video of your Honda being accurately measured at over 150, I will send you a $100 gift card for pep boys or wherever you shop for muffler tips, glasspacks & gutter guard. I *really* will. I will even even spring for expedited shipping Joey. Merry Christmas & Happy tuning.

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