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Old 06-05-2003, 04:46 AM   #1
makofoto
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Default What is the conversion factor to go from Wheel HP to Crank HP?

What is the conversion factor to go from Wheel HP to Crank HP?
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Old 06-05-2003, 08:10 AM   #2
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there is no fixed conversion, but X 1.3 will be reasonably close. But some dynos give higher losses, meaning lower WHP figures.

Paul
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Old 06-06-2003, 01:27 AM   #3
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Take wheel hp and add 25% to that number. That's pretty accurate for the WRX.

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Old 06-06-2003, 01:35 AM   #4
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I like 1.3X better ....
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Old 06-06-2003, 01:20 PM   #5
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WHP/.74 = FWHP

Example = stock WRX claims 227 FWHP, dynos 167 WHP on average. That's about a 26% drivetrain loss. Dividing the WHP by .74 is the same as multiplying the FWHP to estimate the WHP.

I'm pretty sure this is fairly accurate, but since I'm not a rocket (or automotive) scientist I may be off base a bit...
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Old 06-06-2003, 05:54 PM   #6
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Old 06-06-2003, 11:28 PM   #7
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Flat420.. Same as my technique.. 25% to 26% seems most accurate for WRXs.

Jay
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Old 06-07-2003, 05:48 PM   #8
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It seems that some people aren't clear of what's being said here.

whp/0.76 = flywheel hp

is the same as

whp *1.32 = flywheel hp

The above represents 24% losses, so take 24% from the flywheel figure to get wheel hp, OR add 32% to the wheel hp to get flywheel.

Paul
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Old 06-07-2003, 07:57 PM   #9
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That would mean a stock 2.5 RS is puttin 122.1 hp to the wheels?! Hmm, I didn't think we put down that much...
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Old 06-08-2003, 08:03 AM   #10
Pavlo
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Depends how you measure it.

But you could be right, those conversion factors seem to fit with cars that have power levels in the stock WRX to 300whp region.

It's also dependant on road speed, so the losses I mentioned are typically in 4th gear at the power peak, which equates to about 110mph.

THe losses aren't that simple, but the conversion is pretty good when looking at setups within a specific range.

Paul
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Old 06-09-2003, 07:04 PM   #11
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So if an AWD Impreza has about a 25% loss, would it be safe to say my FWD Impreza has about a 12.5% loss?
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Old 06-11-2003, 03:19 AM   #12
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DO you only have 2 wheels? Only have half a gearset?

Drive line losses also include a considerable amount of tyre losses. Not to mention bearing drag of free running wheels.

My guess would be higher, but less than 20%. The 4wd system adds a propshaft, rear diff and shafts, not a massive extra.

Paul
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