There are so many dynos in different conditions and the dynos can give you different results. People often talks about horsepower.
Me and my little stocktwin supra has won over 750hp singleturbos. The horsepower means nothing if you can´t handle it.. Bring it to the racetrack and show what you got.
My car has regular euro turbos, Aem v2, other camshafts/camgears.
I have never installed a nitro system and I run my car on Shell Vpower 99 octane.
With this combo we have managed to run a 11.38/122.5 at the racetrack.
The dyno has given us EXACT numbers of 486rwhp. I´m sorry, i should have written APPROXIMATELY 500RWHP!
I´m a blonde girl you know so please forgive me!
But still...there isn't an exact formula since too many variables can affect the drivetrain loss, but a general rule of thumb is to subtract ~10-20% from flywheel HP to get an approximate RWHP. Again, it's different from car to car, it's a rough estimate.
So I say it again...the track shows if you have a fast car...of course you need to be able to drive good to!