[marcocsx3121]

Your chassis dyno numbers are definitely lower than I would expect based on the engine dyno sheet. As an earlier post correctly indicated, there are a number of variables that can have a fairly dramatic effect on rear wheel horsepower.

As an aside, I drove the twin of your car (Brock coupe, 408 Roush) a couple of months ago, and based on my seat of the pants dyno, I'd say that mid to high 300s at the wheels felt about right.