rwhp vs crank hp

[ja burna]

Does anyone know a formula or off the top of their head what 324 rwhp equates to in terms of crank hp?

[slammin.e28]

Add 20%

In general 20% driveline loss is the accepted #, but it varies car to car.

[LJ851]

15-20 percent is usually whats used on a 2wd vehicle.

[10Toes]

http://www.mk5cortinaestate.co.uk/calculator4.php

[IronFreak]

Agreed, I read a car craft article a while back, they said average a manual eats about 18-20% of the power, while an auto eats upwards of 32-35% of power.

[ak-]

15-20 percent is usually whats used on a 2wd vehicle.


324x .82 = 265 at the crank. 18% loss.

You did it backwards.
He was 324 wheel.

[P Arkus]

You did it backwards.
He was 324 wheel.

^^^This. Using your formula of 18%, it should be 324 x 1.18 = 382 Crank HP

[Cabriolet]

^^^This. Using your formula of 18%, it should be 324 x 1.22 = 395 Crank HP

Fixed your math issue.
It's a ~400hp engine

[ak-]

Fixed your math issue.
It's a ~400hp engine

What's his math issue? 18% vs 22%? lol

[VinniE30]

I've read it's around 15% for manual and around 20% for auto.(autos are more variable though since newer ones are more efficient.
I would say 15% for a rear wheel drive manual BMW.
Lets take the e36 m3 for example.
They usually dyno 200-210WHP bone stock. (dynojet)
They are rated at 240HP by BMW.(CHP)
240 - 15% drivetrain loss = 205 WHP so the 15% works out perfectly for that example.

edit:
OP, using 15% you would have 324 x 1.15 = 372.6 crank HP.

Also, you have to consider that different dynos typically read higher and lower than others, some are at shops to be used for tuning only, not for bragging rights, so they don't change it from the factory settings which may be conservative. So I would ask the place that it got dyno'd at (or the dyno manufacturer if they don't know) because they would know how their reading correlate to crank HP better than anyone.

[Cabriolet]

What's his math issue? 18% vs 22%? lol

na dude. bad math is bad. 1.22 is 18% (1/(1-.18)) = 1.2195

[ja burna]

yeah figures were using a Mustang dyno.. so I don't know if they read lower or higher

[VinniE30]

yeah figures were using a Mustang dyno.. so I don't know if they read lower or higher

They read lower than dynojet with the factory settings, but sometimes shops add in a correction factor to make customers happy with higher numbers, but that can be done on any dyno I believe.
Look at this article on dynos and how much higher/lower different manufacturers' dynos can be.

http://www.hotrod.com/techfaq/hrdp_0405_chassis_dyno_guide/viewall.html

Also see this thread: http://forums.bimmerforums.com/forum....php?t=1696183

And if comparing to a reading done on a different day or different place you have to consider how factors like temperature and altitude affect output.

[nando]

forget about calculating crank HP from a wheel dyno. it's totally pointless. not only does it change with ambient conditions, it changes with dynos, and the % is not linear - it changes for the same drivetrain based on how much power you put into it.

adding a magic 20% number, guessed from something you read on the internet (or pulled out of your ass, usually), to a wheel dyno result so you can brag about your mad HPs is one of the lamest bench racing excersizes there is. Chassis dynos are a tool used to tune an engine. That's all. The only comparisons should be cars done on the same dyno in the same conditions.

[LJ851]

Fixed my math issue, and nando is correct. Too many variables to make the calc anything but a wild ass guess.