1979 115 (140hp) johnson prop questions

[rjcamel2355]

I have a 1979 Johnson 140hp 2 stroke bored .020" on a 1984 14ft tide craft boat (800#). 8" Jackplate currently running a 20pitch ss raker wot 6500-7000rpms (tach bottoms out at 6500). I'm seeking a better prop, trying to run a cleaver surface piercing for more speed. I have a 4" hub lower unit and a 3 1/4" Ron hill 23pitch cleaver propeller that I want to run run. I spoke to Ron hill in regards to this and he told me in Canada they run 3 1/4" props on 4" cases. But it's on lightweight boats with the exhaust reliefs cut above the water. Has anyone else tried something similar to this? I'm thinking of cutting the exhaust out in a rectangle shape where the current exhaust holes are (to release the exhaust up top instead of over my prop blades due to cavitation problems I am experiencing)