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Crank HP from RWHP formula?

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Old Sep 17, 2011 | 10:48 AM
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Default Crank HP from RWHP formula?
Anyone have a good rule of thumb, or formula worked out, to determine crank HP from a given RWHP?

I realize that dyno numbers very from dyno to dyno, and that certain gear/drive train combos can also affect true HP. Just wondering if there is a fairly reliable way to calculate crank HP from known RWHP.

Thanks,

S
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Old Sep 17, 2011 | 05:54 PM
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every car is different. a six speed might be 12%. an unlocked auto might be 20%. its a hard ? to answer. theres really is no rule of thumb.
Last edited by m1a2d3; Sep 18, 2011 at 05:57 AM.
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Old Sep 18, 2011 | 07:08 AM
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RWHP Divided by 85% for a Stick car or RWHP Divided by 80% for a Auto tells Crank HP.
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Old Sep 18, 2011 | 11:05 AM
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Originally Posted by blk/slvr02ss
RWHP Divided by 85% for a Stick car or RWHP Divided by 80% for a Auto tells Crank HP.
Ok thanks!
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Old Sep 18, 2011 | 11:55 AM
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FWIW: My build made 656HP on the engine dyno and 577RWHP on a DJ. The 15% figure works on some..not on others. As HP increase the % loss goes down.
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Old Sep 18, 2011 | 12:03 PM
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Originally Posted by WKMCD
FWIW: My build made 656HP on the engine dyno and 577RWHP on a DJ. The 15% figure works on some..not on others. As HP increase the % loss goes down.
Cool, thanks. Going to have my new motor dyno tuned and was kicking around the idea of having some HP badges made. Don't like the black Z28 factory badges on my black car, don't really want to have them in chrome, so I found a site that will custom make a HP badge. I am sure that even after I get the HP numbers I will order a conservative number for the badges, but I think it would be cool.

Thanks again.

S
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Old Sep 18, 2011 | 12:21 PM
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http://www.westcoastcorvette.com/p-3...bers-only.aspx

I think all chrome badge in place of the Z28 badge will be sweet.

S
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Old Sep 18, 2011 | 01:40 PM
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Originally Posted by blk/slvr02ss
RWHP Divided by 85% for a Stick car or RWHP Divided by 80% for a Auto GUESSES Crank HP.
Fixed it for ya!
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Old Sep 26, 2011 | 08:32 PM
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Originally Posted by WKMCD
FWIW: My build made 656HP on the engine dyno and 577RWHP on a DJ. The 15% figure works on some..not on others. As HP increase the % loss goes down.
This is very true & I have seen it more that once. It seems that the 15% / 20% rule is a guess on anything above 500 crank hp. It gets you close though. The lower the power numbers, the more accurate the formula is. Wierd !
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Old Sep 26, 2011 | 08:40 PM
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What i exactly do is im about 350 rwhp and just do 350/.85= 411.76 Hp and im 355 rwtq so its 355/.85= 417.64 Tq. Thats 15% for manual is what i usually go by and auto might be about 17-18% but some will say up to 20 depending on drivetrain and so on.
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