Both Good motors Not gone to say any thing Bad about the Nova Plus 21-4. I would run the Cobra motor i have had Nova motors good Motors but the Price to fix the Motor is Higher that way i went with Axe Rossi motors for so many years. Rods are only 45.00 bucks and a new Piston and sleeve for the Cobra is only 110.00 Bucks Price a Rod and a Piston and Sleeve for a Nova Plus 21-4 a Lot higher and if you are on a Budget like i am you will wont to fix the motor some time and not just buy a new motor. Amain dose not even have Parts for the Nova21-4 in Stock.