What is the conversion factor to go from Wheel HP to Crank HP?

makofoto · 06-05-2003, 05:46 AM

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Pavlo · 06-05-2003, 09:10 AM

there is no fixed conversion, but X 1.3 will be reasonably close. But some dynos give higher losses, meaning lower WHP figures.

Paul

Diversion · 06-06-2003, 02:27 AM

Take wheel hp and add 25% to that number. That's pretty accurate for the WRX.

Jay

makofoto · 06-06-2003, 02:35 AM

I like 1.3X better ....

Flat420 · 06-06-2003, 02:20 PM

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...

Mattr762 · 06-06-2003, 06:54 PM

Just use THIS CALCULATOR.

Diversion · 06-07-2003, 12:28 AM

Flat420.. Same as my technique.. 25% to 26% seems most accurate for WRXs.

Jay

Pavlo · 06-07-2003, 06:48 PM

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

Ruff · 06-07-2003, 08:57 PM

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...

Pavlo · 06-08-2003, 09:03 AM

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

DoinkMobb · 06-09-2003, 08:04 PM

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?

Pavlo · 06-11-2003, 04:19 AM

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

06-05-2003, 05:46 AM	#1
makofoto Scooby Guru Member#: 25243 Join Date: Sep 2002 Chapter/Region: SCIC Location: South Pasadena, CA Vehicle: 2006 Legacy Outback Blue	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? * Registered users of the site do not see these ads.

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06-05-2003, 09:10 AM	#2
Pavlo Scooby Specialist Member#: 23015 Join Date: Aug 2002 Location: Wellingborough, UK Vehicle: 95-> GC8 Black, blue and blue	there is no fixed conversion, but X 1.3 will be reasonably close. But some dynos give higher losses, meaning lower WHP figures. Paul

06-06-2003, 02:27 AM	#3
Diversion Scooby Specialist Member#: 18651 Join Date: May 2002 Chapter/Region: South East Location: Jacksonville, Florida Vehicle: 2013 Civic Si Sedan PMM	Take wheel hp and add 25% to that number. That's pretty accurate for the WRX. Jay

06-06-2003, 02:35 AM	#4
makofoto Scooby Guru Member#: 25243 Join Date: Sep 2002 Chapter/Region: SCIC Location: South Pasadena, CA Vehicle: 2006 Legacy Outback Blue	I like 1.3X better ....

06-06-2003, 02:20 PM	#5
Flat420 Scooby Newbie Member#: 35455 Join Date: Apr 2003 Chapter/Region: SCIC Location: San Diego-Home of the Chargers Vehicle: 07 LGT Spec.B Stg2 DGM	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...

06-06-2003, 06:54 PM	#6
Mattr762 Scooby Newbie Member#: 31624 Join Date: Jan 2003 Location: Tulsa, OK Vehicle: 02 WRX White uppipe, turbo-back, MBC	Just use THIS CALCULATOR.

06-07-2003, 12:28 AM	#7
Diversion Scooby Specialist Member#: 18651 Join Date: May 2002 Chapter/Region: South East Location: Jacksonville, Florida Vehicle: 2013 Civic Si Sedan PMM	Flat420.. Same as my technique.. 25% to 26% seems most accurate for WRXs. Jay

06-07-2003, 06:48 PM	#8
Pavlo Scooby Specialist Member#: 23015 Join Date: Aug 2002 Location: Wellingborough, UK Vehicle: 95-> GC8 Black, blue and blue	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

06-07-2003, 08:57 PM	#9
Ruff Scooby Specialist Member#: 32131 Join Date: Jan 2003 Chapter/Region: NWIC Location: Oregon City, OR Vehicle: 2006 Nissan 350Z Was 01 2.5 RS	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...

06-08-2003, 09:03 AM	#10
Pavlo Scooby Specialist Member#: 23015 Join Date: Aug 2002 Location: Wellingborough, UK Vehicle: 95-> GC8 Black, blue and blue	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

06-09-2003, 08:04 PM	#11
DoinkMobb Scooby Specialist Member#: 3787 Join Date: Jan 2001 Chapter/Region: South East Location: G-ville Vehicle: 2008 Gay Car	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?

06-11-2003, 04:19 AM	#12
Pavlo Scooby Specialist Member#: 23015 Join Date: Aug 2002 Location: Wellingborough, UK Vehicle: 95-> GC8 Black, blue and blue	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