[patrickt]

There are at least three distinct numbers for everyone's build. 1) The engine as dyno'd by the engine builder (usually open headers, maybe no water pump, certainly no accessories), other adjustments that tend to "up" the number; 2) The true flywheel horsepower number that the car has with the engine installed and everything hooked up but as if there was no transmission in the car and a dyno was attached to the flywheel; 3) The rear wheel horsepower as measured with a chassis dyno. 1>2>3, often times by pretty large percentages. #1 might be in the 500s, while #3 might be in the 300s.