[Stealth]

1) Is the CYMA Motor a ferrous or neo motor?
2) The piston head and shell have nothing to do with your ROF, your shimming is everything. People think shimming is easy, and for the most part, it is. But time and time again, John will always shim something better than me, because he takes an hour to shim a mechbox to perfection and I take 30 minutes.
3) Using a lighter piston never hurts but this is probably not the source of your problem. Nobody should still be using aluminum piston heads and metal washers these days.


Some suggestions to increase your existing system efficiency:
1) Before you step up to a mosfet, upgrade the wiring to 16awg minimum and use a CONTINUOUS length of wire, each connection/solder joint you make is going to introduce parasitic resistance across the system.
2) Re-shim. Go to bearing bushings, although if you shimmed correctly it shouldn't make a huge difference.
3) Remove all unnecessary weight off the piston
4) Test that there is free movement of piston along its entire stroke
5) Ensure that the bearing spring guide's bearings are smooth
6) Test out airseal - should seal with the piston moving quickly, and allow air if moving slowly.

You're going to hear me say it again, you're setting yourself up for failure since you're constrained by space. Most people would naturally realize the space benefits of a lipo battery and go that route. Anyway, you need the extra power of a higher-voltage battery. If you are going to stay NIMH, like TC said, you'll need to go to 10.8v, but then, what's the point? You might as well go lipo at that point and enjoy the additional power an equivalently-sized 11.1v lipo will give. Drop in one of the Traxxas mini batteries and I'll guarantee you're going to be up at 30rps instantly.