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However the dyno didn't have an exhaust system on it, we do, how much is that worth?


There is a way to answer that question. smoke

Taking the net hp and multiplying it by the correction factor for that run gets you within 30-35hp of your dyno numbers.
I have to believe that “some” of that missing power is being lost with the exhaust system.

Did you try the 1/4 mile version of that calculator to see how the numbers compare?

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads