Most new car mags (eg MOTOR, Wheels) will quote flywheel figures. These are usually obtained from the manufacturer.
Eg: A brand new Nissan 33GTS25t made 185kw at the engine. A brand new HSV GTS makes 300kw at the engine.
Accurate flywheel figures can only be obtained when the engine is out of the car and set up on an engine dyno.
Guesstimates about the flywheel figures can be made from "at the wheels" readings by factoring in some amount of drivetrain loss.
Eg: If I make 138rwkw in a stock 33GTS25t, and I use a drivetrain loss of 35%, I should be making about 186kw at the engine...
138 x 135% = 186.3
Different amounts of drivetrain loss are found with different types of drivetrains.
Eg: RWD might be 30% loss. 4WD might be 40% loss. Etc...
Hope this helps...