How much power do engine mods yield?

Reportedly Tilly is doing that on 18psi of boost. On the The H,A,M,B there is a thread on six cylinder drag cars from the '70s on. These are mostly class racers. There are reported A-Bodies running 11's, 12's and 13 second times. Class racing doesn't involve nitrous or turbos just very detailed and thought out combinations. How did they do it, who knows those guys don't post on the Internet and didn't share secrets.

Don Dolmetch has been running a 225 powerd FED dragster as a hobby. He has been building engines for a long time. He has some threads on the H.A.M.B detailing what he has done to the engine. His ideas and experimentation has definitely gone down a different path then most. His contention is that the head is not a bad as some have proclaimed. With a proper port job and cam, the 4.125" stroke is actaully a benefit to filling the cylinder. He may be onto something, his dragster is able to run with other cars with twice the engine size and he proclaims that it is "scary" fast.

My own experimentation has shown me that the 225 doesn't respond like a v8 would with a given combination. For an example, many have said that the stock fuel pump and fuel lines are more then good enough. I have found that they are marginal at best.