Ernie,
NASCAR gets 800+ horsepower out of their small blocks and they have to use flat tappet lifters. You should easily be able to top that with your Big Block even going to flat tappet lifters. Mine with the mild build and lowering the cam to make it driveable dynoed out at 440 H.P.at 6300. That is more than I really needed or was wanting but so far I like it ok. We are going in different directions as I am tired of high powered temperamental motors that blow up. But as stated in an earlier thread, Big Block = Bigger Bang when it blows. Sorry to hear about your bad luck. Keep us posted on what you decide. Maybe lower compression and twin turbos.
Ron
