Is there a general rule of thumb for converting bhp to rwhp? This is for a '70 BB. Not sure yet what engine, because it's not built yet. May be close to a crate with 440hp and a TKO600. Thanks for the help!

I thought that if you ran that in front of a TH400, that it would be approx. 20% loss through the drivetrain..and that a manual would only be about 15% loss..these are very rough figures and may be on the conservative side. Also, I had also read that a TH350 would suck up less power than a TH400..so maybe that would be more on par with a manual at the back wheels. Best way is to strap it down and run it!

I thought that if you ran that in front of a TH400, that it would be approx. 20% loss through the drivetrain..and that a manual would only be about 15% lossBetter to think in terms of *amount* of horsepower lost instead of *percentage* lost...a TH400 behind a 4-cylinder is gonna eat the same amount of power as it would behind a blown BBC. So it may be a 20% loss behind the 4-cylinder but only a 10% loss behind the blown BBC.

Anyway, I think the number is around 40hp +/- to turn a TH400...and a TH350, or a manual tranny, would be less. That, of course, is what they make light weight internals for... ;)

Thank you both. That's the sort of ballpark figure I was looking for. Now if I can just estimate some ET's... smile.gif

Here are some good online calculators...the most accurate way to calculate HP is from MPH #s...

http://www.stealth316.com/2-calc-hp-et-mph.htm

Originally posted by Chevy454:
</font><blockquote>quote:</font><hr />I thought that if you ran that in front of a TH400, that it would be approx. 20% loss through the drivetrain..and that a manual would only be about 15% lossBetter to think in terms of *amount* of horsepower lost instead of *percentage* lost...a TH400 behind a 4-cylinder is gonna eat the same amount of power as it would behind a blown BBC. So it may be a 20% loss behind the 4-cylinder but only a 10% loss behind the blown BBC.

Anyway, I think the number is around 40hp +/- to turn a TH400...and a TH350, or a manual tranny, would be less. That, of course, is what they make light weight internals for... ;) </font>[/QUOTE]Doesn't work that way. It is a % because a blown big block will accelerate much harder than a 4 cylinder. So the frictional losses from turning the trans, rear gears, axles, etc. will be much higher. At a steady state there should be an equal loss between these two different engines, but not under full throttle.

Jody

The percentage thing will get you pretty close. The manual transmission will only loose about 13%, while the Turbo 400 will come in at about 20% and the Turbo 350 about 19%. None will be as low as 10%, ever. You can use the old Chrysler drag formula if you convert the MPH to reflect the changed method of measuring trap speed.(New speed times 1.0072 = old trap speed.) To Chevy 454, Your charts were interesting but i find only Patrick Hale's to closely approximate what my son's car actually runs, as the EPA new car sticker says, "your results may vary".