I found this a couple years ago in a forum. Don't know who wrote it, but it might be of interest to someone trying to soup up an FP40.

"Racing the Magnum GP40 (clone of the FP) for club-level racing, it had to be "stock", but there are a few things you can do. 1) Back out the spray bar so that it does not project into the carb throat. Just loosen the jam nut, back it out until it is flush with the side of the barrel, and retighten the jam nut. 2) Try removing the head gasket; this helped with most engines, but not all, so experiment. On the OS25, the plain-bearing engines have .016 head gasket, while the BB engines have a .008 head gasket, so if removing the head gasket does not help, you might try a .40FX head gasket - it might split the difference. It might not meet the strict interpretation of the rules - not sure on that. 3) If you remove the head gasket, you might start blowing plugs. We found the McCoy plugs to hold up much better than others, and use a non-idle-bar plug. 4) Some guys disassembled the engine and lapped the crank / main bearing in an attempt to minimize bearing drag - not sure if that really helped or not - sounds good in theory, but I never tried it 5) Believe it or not, one of the guys discovered that if you run a long plug WITHOUT the plug gasket, he picked up several hundred rpm. I tried it on my engine and son of a gun he was right! Must have had something to do with the placement of the coil in the combustion chamber. 5) Disassemble the muffler and make sure there is no casting flash or machining chips in the exhaust stack or tailpipe openings. Typical rpm on these engines with a 9x6 prop was mid to high 14k range, some guys had stronger engines up in the low 15k range. You might try a 9x7 prop; our event mandated a 9x6, but I tried a 9x7 when test flying and it seemed to give better speed. Purely non-scientific."

You might wanna make sure you don't make contact with the piston before cranking the engine if you follow the tip about removing the glow plug gasket.

GoMike