Peter: For your info Dinan claims +12-13 HP (over a chip and free-flow muffler) when one of their "high flow" intake manifolds is added. They are essentially extrude-honed and of course Dinan charges big bucks (approx. $1000) but I suspect you could send your manifold directly to Extrude Hone (the company) and save a bundle. Just a thought. By the way, what compression ratio are you running and which brand of pistons are you using? And which cam?