If rear wheel HP is 341.What is the approx Fly wheel Hp? Car has A/t Thanks

 

15% drivetrain loss, so 392HP give/take.

 

I'll give you another 9hp over that.

fwhp = (rwhp) / (1 - %loss) = (rwhp) / (1 - .15)

So 341 rwhp is around 401 fwhp, if you assume 15% loss.

It's not exactly the 115% x rwhp = fwhp that most people calculate. Either Injuneer or Shoebox had a pretty clear explanation of fwhp vs. rwhp.

 

auto trans is higher % loss than a manual...

so it is car specific to an extent

 

No way to know for sure, but what was posted will put you in the ballpark. There are different kinds of chassis dynos and different kinds of engine dynos. Each can be used in a variety of ways. For example, engine dynos can use a variety of "sweep rates" - the rate at which the engine is allowed to accelerate. Even this small difference (300 v. 600rpm/sec., for example) will change the measured power output. Also, correction factors are typically used to compensate for differences in air density. The CF used can drastically change the reported power output. AFAIK, there is no "gold standard" - the measurement method needs to be specified to make best use of the data.

It is a matter of debate which method best correlates with performance, which is what really counts after all. One thing we do know is that it's "area under the curve" within the usable rev range that counts more than peak hp/torque. Also, the rev range is important - power developed higher up allows the use of shorter gears and more torque delievered to the wheels.

Rich

 

If that's true then how are stock autos able to dyno in the 135-145 range!? That's a tad high don't you think?