I saw a test on them in a magazine where they got 500 hp with a stock 5.0 short block with them and a big ass cam. I've read lots of good things about the work John Kasse's done, the guy's a whiz with Fords. If I had the money and was in th emarket for heads and wanted the best, those are the best you can get for a windsor headed small block. His heads are also marketed under Ford Racing's name too.