Powerloss through drive train

The old GTX makes 830 hp on the pump, and on the rollers with a full ex system with tail pipes it made 700 hp..
From what I've seen stick cars run at best 12% to as high as 18%.
Now auto cars are all over the place,depending on the condition of the converter and how restrictive the ex system is..
A customer took his 600 hp 440 Cuda to a chassis dyno and it made 395 hp at the wheels.This is an 11.50@118 mph 355 gear car.
This would be a car with an unhappy converter now,
just my two cents...