For the most dependable and assurances that they will remain that way you have two choices, three if you add the seller with aftermarket modifications. Brillelli and Zenoah. Ralph Cunningham/RC Ignitions does some neat little modifications that make the Zenoah even better while including a lifetime warranty on the ignition.

Others can say they are as dependable and have the power but none have the track record of Zenoah. No ifs, ands, or buts, and zero room for arguement. Both engines have excellent service availability. Brillelli through Brillelli, and Zenoah through Horizon and Ralph Cunningham. If you stuff a Zenoah nobody does repairs more reasonable than Cunningham. So you can buy cheaper but not better.