I've heard that its really hard to get past mid 50's on HP with those, I was talking to one builder (A very reputable one) about them, he was working one while I was there, he told that all he could get out of it on his dyno was about 54hp if I remember right, so he called another reputable builder and talked to him about his concerns and the other builder told him that that's all he is going to get and to tell the owner to enjoy it with all of it's other features.