The O.S. Max .55 AX Aircraft Engine with Muffler is better than ever, with an improved carburettor and muffler. You get the same phenomenal power, with the convenience and safety of a rear angled needle valve on the carb and a squared-off muffler for easier cowling installation. If you want .50 scale power that fits conveniently in .40 size planes, get the 55AX and get flying!