Well, it's already been mentioned, but with E85 and Edelbrock heads 600 is not out of the question. The 408 in my truck made 578 hp with a Hughes solid flat tappet at 6200rpm. The compression is about 12.7 to 1 with the Keith Black forged flattops. With a 4000 stall and 3.91 gears I drive it to the track and run 11.50's at 4900 feet elevation. Very driveable, and with the added compression I'm getting right at 15 mpg as well!