If you are putting 200HP at the rear wheels what are you putting at the fly wheel. Is there an equation?

I'm to lazy to do the math... but most people here with 4L80E trannies calculate with about a 20% drivetrain loss.

That will be roughly 250 at the crank with an auto. There is no real accurate way to go from the wheels to the flywheel and back, since every truck and drivetrain is different. On average, as Green Machine stated, there's about a 20% loss in the drivetrain with an auto.

That will be roughly 250 at the crank with an auto. There is no real accurate way to go from the wheels to the flywheel and back, since every truck and drivetrain is different. On average, as Green Machine stated, there's about a 20% loss in the drivetrain with an auto.

Sure there is, dyno truck for RW numbers, then pull engine and dyno for flywheel numbers. divide RW from Flywheel, and that's the loss.

200 RWHP = 240 Flywheel HP. 20% loss is what is used as the rule of thumb when doing calculations, it's ment for a rough guess more then a factual number.

Sure there is, dyno truck for RW numbers, then pull engine and dyno for flywheel numbers. divide RW from Flywheel, and that's the loss.

200 RWHP = 240 Flywheel HP. 20% loss is what is used as the rule of thumb when doing calculations, it's ment for a rough guess more then a factual number.

But I'm not sure that's what the OP is asking. I think he's asking more along the lines of finding out without pulling the engine. But yes, that will work. I think your number may be more accurate anyways, at least for my truck. Turbine Doc's dyno numbers of a stock truck, almost identicle drivetrain to mine, shows he made 84.4% rated power. That's a loss of about 16%. Your numbers come out to 16%. Still not perfectly accurate, since every truck is different, but should be close enough.
Anyways, here is my work for 20%:

X=flywheel horsepower, 20%=.2
X-.2X=200 <beginning equation
.8X=200 <combine like terms
/.8X .8X <devide both sides by .8X
X=250

Now, to check it:

250*.2=50
250-50=200