I guess you tired almost everything that I would have done to try to pick the engine up power wise....and it didnt work.
![](/ubbthreads/images/graemlins/frown.gif)
But Like mentioned, that engine might perform as well as any other engine that makes 600hp on someone Else's dyno.
Those heads on that large of a engine will make more torque, than all out hp...
You need a way to extend the RPM range another 700-1000 rpm....then hp has no other choice but to follow.
I remember the first time down the track with a 4.15 stroke engine, and box stock edelbrock heads....It pulled good till about 5800 rpm's..Then it was literally like running the car against a brick wall...the nose fell down...I knew it was going to be a mid range rpm engine...