I also have an Axis that I bought about 10 years ago. I replaced the Torq .21 engine with a Ofna Force P-4 which was alot
faster than the Torq .21. The problem is the Axis requires a treaded crank .21 engine not a SG style crank. Engine companies do not make treaded crank .21's anymore. The only thing I could tell you is to fix your Torq .21. Tower Hobbies
still sells the piston and sleeve for that engine. The Force P-4 treaded crank has been discontinued.

P/S. I wouldn't really want to race the Duratrax Axis though.