I see very little posted here concerning minor engine mods to free up horsepower. I have been building and Hot Rodding automotive engines for years so I feel qualified to bring up the subject. I recently obtained a used Thunder Tiger GP 42 in less than stellar shape so I used it as a guinea pig of sorts to see if I could get some horsepower . The engine wasn't beat just had not been cared for properly. Compression was good and the internals are excellent. I fully disassembled the engine and noticed the bypass ports in the crankcase had a lot of flash and sharp edges. By simply removing the flash and smoothing the transition from block to port I feel I have gained a lot of flow. I do not have any before figures but I can say that this engine will now totally blow away my OS 46 LA, an engine of similar design (plain bearing, medium price) by a very significant margin(almost a half pound of thrust on an 11X6 MA). I am not bashing OS !! My LA runs great but now my TT 42 runs better! I still have a few tricks up my sleeve fot my GP. If this performance is typical for the GP 42 please let me know as I said I have no "Before" numbers because the sad shape the engine was in. Let me add, the same plug, fuel and prop were used on both engines for consistency. I plan on doing this procedure to a lot more of my engines . Like my single port Cox 049 production engine that now turns an APC 5.7X3 to 16,700. Thanks to Probrojoe.