I think Steve was talking about the horspower capablities of the Shelby block which is supposedly 1500 hp. Steve is correct about the average FE head only flowing as well as an aftermarket small block head. The average flow #s for a nicely ported set of E-brock FEs for a 390/428 with the smaller 2.09/1.66 valves is around 300 to 310 intake and 200/210 exh. I am building a supercharged 331 small block at this time that has a ported set of AFR 185s that flow
305 intake and 227 exh. It is not hard to understand why it is so easy to make a 500 to 550 hp 408 Windsor.
My Dove tunnel port heads will flow about 400 cfm intake and 260 exh
with a lot of work on the exhaust port.
The iron tunnel port heads I posted a photo of earlier in this post
flow 380 intake and 248 exh @ .700 lift I did tons of work on them to get that much flow.
The only way a FE will make 1500 hp is with a radical set of heads and a big turbo or supercharger. And maybe some N2O
as well
Unless of course you have a blown, injected cammer on nitro which was state of the art NHRA fop fuel circa 1968/69 Then you'd have about 2000 to 2500 hp
--Mike