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Old 05-23-2003, 12:28 AM   #1
snoopewite
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A Question Of Power

I'd appreciate it if someone could explain the rule for estimating the power to the wheels of a car after finding out the power to the crank. I'd also like to know if there's a difference between the power at the crank and the power at the flywheel.
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Old 05-23-2003, 01:25 AM   #2
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Re: A Question Of Power

Quote:
Originally Posted by snoopewite
I'd appreciate it if someone could explain the rule for estimating the power to the wheels of a car after finding out the power to the crank. I'd also like to know if there's a difference between the power at the crank and the power at the flywheel.

Second question first. The answer is no.

First question second. Snoope, there is no "rule". There are too many variables such as type of transmission (auto or manual), drivetrain layout, etc. You can take two measurements on the same car with the same engine and transmission but a different differential and get different results. How efficient is this particular component, what type of lubricants are being used, etc, etc, etc, (hey Ma look at me I'm Yul Brenner).

So.... if you can get 90% efficiency your doing damn good. Most cars will be closer to 75-80%.

Snoope, I got a question for you. I really enjoy answering most of your posts, but where the hell do you come up with this stuff? See ya.
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Old 05-23-2003, 03:10 PM   #3
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Re: A Question Of Power

Quote:
Originally Posted by snoopewite
I'd appreciate it if someone could explain the rule for estimating the power to the wheels of a car after finding out the power to the crank. I'd also like to know if there's a difference between the power at the crank and the power at the flywheel.

Just put it on a dyno. Much easier
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Old 05-24-2003, 05:52 PM   #4
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Firstly, thanks 57OCK for recommending a dynamometer session although it was a hypothetical question.
Thanks for answering my questions vwhobo.
I’ve got the automotive knowledge that I know from outside this forum from books, magazines, price guides, videos, programmes and websites.
I’d never make a mechanic because I’m not much good at the practical stuff and I’ve not had any experience with performance cars because I’m 20 and my insurance is high.
The thing is that I’m a deep thinker (notice chess and religion in my profile) and I enjoy thinking and talking about cars.
I came up with this topic because the power figures on that “Suprastore” site were to the crank. I noticed that the power that was mentioned at the wheels after dynamometer sessions didn’t add up with the rule that I’ve been using. I wanted to check that there wasn’t a difference between power at the crank and power at the flywheel because the power figures on the quarter mile calculator that I’ve been using have to be entered at the flywheel. I’ve been adding 25% onto the theoretical power to the wheels and then entering that figure which is as good an estimation as any seeing as like you said “there is no rule”.
Here’s another question for you vwhobo – Am I right in thinking that you have your own chain of garages/car shops?
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Old 05-24-2003, 09:09 PM   #5
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Quote:
Originally Posted by snoopewite
Firstly, thanks 57OCK for recommending a dynamometer session although it was a hypothetical question.
Thanks for answering my questions vwhobo.
Iíve got the automotive knowledge that I know from outside this forum from books, magazines, price guides, videos, programmes and websites.
Iíd never make a mechanic because Iím not much good at the practical stuff and Iíve not had any experience with performance cars because Iím 20 and my insurance is high.
The thing is that Iím a deep thinker (notice chess and religion in my profile) and I enjoy thinking and talking about cars.
I came up with this topic because the power figures on that ďSuprastoreĒ site were to the crank. I noticed that the power that was mentioned at the wheels after dynamometer sessions didnít add up with the rule that Iíve been using. I wanted to check that there wasnít a difference between power at the crank and power at the flywheel because the power figures on the quarter mile calculator that Iíve been using have to be entered at the flywheel. Iíve been adding 25% onto the theoretical power to the wheels and then entering that figure which is as good an estimation as any seeing as like you said: ďthere is no ruleĒ.
Hereís another question for you vwhobo Ė Am I right in thinking that you have your own chain of garages/car shops?


Snoope, bingo you win the prize. I wouldn't call them a chain, let's just say a few local independent auto repair centers. The thing is I would rather work on cars than run the shops so I have people do that for me and stick mostly to what makes me happy. It's great to be a gearhead!
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