I have a Goldberg Protege. The original engine recommendation for that plane was an OS 55 AX but I couldn't get one at the time so I opted for the OS 75 AX. Absolutely no regrets with that engine. It's a power house and starts and runs great, right out of the box. This engine pulls that Protege, which, by the way, is as large as the Four Star 60 and the Goldberg Tiger 60, like a much larger engine.

I highly recommend that.

As far as four strokes is concerned, the only reason I didn't opt for one is that they were a bit more expensive and I was a bit unfamiliar with them. I have to ditto all of the above in support of them.

I have three OS 1.20 AX's and love them and the 75 runs as well as those do. But, if you prefer four strokes, I can't think of any negatives that may change your mind. They are fine engines. Lots of torque, and sound realistic too.

CGr.