what formula is used to convert rear wheel hp to flywheel hp

or vice versa. thank you.

 

There's no formlula exactly. It's just less at the wheels. How much varies depending on tranny, gearing and type. Generally 15% to 20%. And there's a wide variation between chassis dynomometers as well. This all makes using rwhp numbers difficult. Comparing similar cars, or one car with mods, on one dyno is about the best that can be done.

 

It depends on who you talk to. Many will say 15% loss for stick and
20% for automatics. So 316 crank hp x .8 = 252.8 rwhp on an auto S4 or
x .85 = 268.6 rwhp on a stick. So thats a drivetrain loss of 63.2 and 47.4.
Some people use 10% for stick and 15% for an auto.

To get crank hp take rwhp / .80 or .85, so 260 rwhp / .80 = 325 crank
hp on an auto.

This is for "stock" engines. When you go to modified engines, some
people use the "stock" formula, and others will take the rwhp and add
the drivetrain loss from the stock configuration. I.e. 492 rwhp on a
S4 5sp would be 539.4 by the addition method and 578.8 by the
"stock" formula. Most people like the 578.8 number, but the 539.4
number is probably closer. Not too many people have the resources
to check on both types of dynos.

 

Not too many folk running around with over 500Hp either..not yet at least.

I like the 578 HP number personnaly. Ill take mine at the rear wheels please.

 

http://www.superstang.com/horsepower.htm