We flew my Sundowner and Evolution 26 combo yesterday and it appeared that the engine was restricted in it's rpm. It was almost like there was a brake of some type. We were spinning an APC 15X10 at 8700 on the ground. OK, not too bad. But the problem was that coming through a dive or turn the engine did not noticably encrease in rpm. If the plane seemed any faster through a dive it would almost immediately loose its speed as soon as it leveled out. The best we could guess was that the Bisson muffler was resricting the engine rpm. I have to assume something is wrong if I enter a dive at 100mph and come out of it at near the same speed.

Any thoughts?

Thank You.