Ive used K&B and OS .61 engines. I then switched to 4 stroke. I have used Saito .72, 80, and .91 engines. for scale realism, the 4 stroke engines are your only choice. If you want top end speed, try a 2 stroke .61. The new Saito .82 is probably the best choice. The .91 had a bit more torque than necessary. The .72 was very scale looking, but a bit short on power for clean aerobatics. The .80 is what I settled on. If I had the money, I would put in the .82. The plane balances perfectly, with no weight added. It is an absolute joy to fly. It looks so real cruising by, but when you give it full throttle, it can go straight up for what seems like forever. Very clean aerobatics. Good luck. You will really enjoy flying the Chipmunk. Mine has been around for about 10 years. I never get tired of flying it.