Originally Posted by
airraptor
QWk, just for reference the OS 25 FX spins a APC 9x6 at 14,000 on 20% nitro and I would guess around 13,000 on 5% nitro so your engine is right in the ball park. You can take out the head gasket and might pick up 200 or so on 5%.
I'd found a few references to the FX, but some were a fair bit higher - probably due to higher nitro. Since I don't have the stock muffler with this engine, I don't have a way to compare the TT muffler I have to the stock one. Nonetheless I'm glad it's running about where it should be. I'll test a couple more mufflers and see what it can do on glow fuel. I may make some port and timing modifications to up the torque to better suit it as a diesel. It's a pretty tame engine with milder timing and smallish carb (6.5mm).
As as for the head shim - without the shim the head clearance is pretty tight. I'd probably need to make a thinner shim. It has a .2mm shim currently. Without the shim the head clearance is .15mm (.0059").