I can attest to the performance with the Power Box muffler installed. It is one great engine. I have it installed on a Goldberg Protege and it has more than enough power for that plane. And as for engine performance, well, I am using a 13.5 x 6 Bolley Prop and this thing has pretty much unlimited vertical. Takes off in about 20 feet on grass with the stock wheels (those puney 2 1/4 inch things) and will fly "all day" at less than half throttle.

I put it on the plane, checked the CG.. right smack on, by the way without any nose weight so the engine was perfect for this plane (won't be the same with others, but based on my experience with some of the Goldberg ARF's, there has been an issue with excessive nose weight to get a correct CG). I then headed out to the field. I fueled it up, primed the engine by going to full throttle, put my finger over the carb and rotated the prop five revolutions. I then attached my glow driver, checked the needle valve and set it to 2.5 turns out from the stop, and hit it with the chicken stick. One flip. ONE FLIP.. and it was running.

I ran it very rich at about 1/4 to 1/2 thorttle for about two to three minutes, then slowly advanced it to full throttle with a very rich mixture and ran it that way for a few minutes.

In other words, I broke the engine in correctly.

After the first tank on the ground, I refueled it, and started it up again. I adjusted the mixture for good full throttle RPM but on the wet side of lean, and checked the transition from idle to full. Perfect. I set the idle, and it was at about 2000 RPM and ran just fine. So, I put it in the air, with only one tank of fuel for break-in. It ran perfectly. Absolutely perfectly. And the power. Wow!!!

A great engine.

I own three OS 1.20 AX engines and all three run exactly like that. Great power, great throttle response, and start very easily.

CGr.