People who have used them have said it makes a noticable difference. I personally got mine more to help spool the big turbo than the actual power gain. It's about 10% bigger so I would expect as much in torque. Don't know about the hp gain since both use the same crappy heads but I would assume the hp curve would be broader and flatter. I like small cams but you can still go bigger with the 4.1.
