If I get 250 rear wheel HP with manual trans
(340, 4spd. power steeing connected, G60 x 15 polyglass, stock exhaust). What is my old fashion fly wheel HP? Thanks.

Probably about 325. But that's a guess. Not as much drivetrain loss with a 4 speed.

Roughly 18-20% loss so about 300-312 at crank

I am not a believer in trying to get a "good" flywheel hp number from a car that was on a chassis dyno. At best,it is a guess.
Chassis dynos can be a great tuning tool if used as such,but to get a flywheel number you need an engine dyno.
I don't intend to make this an argument about which is better/worse,each has it's place. I wish I owned one of each but I had to stick with one.
Keith

Keith you are right. I have seen that when I compared the two known numbers sometimes it did not come close with the normal formula that i follow. I only use it because most of the guys want a number. I use my dyno for mostly a tuning tool and really don't care what the numbers are the car will tell the real story. I wish i could afford both also. Jake

Before I bought my engine dyno I thought about a chassis dyno.....for about 3 seconds. Dave