Super Tigers usually require changing the position of the carb spray bar to get them to run half decent. The throttle barrels also like to suddenly jam in one position leaving you with no throttle control. I won't recommend them! Soooo, the OS engines are easy to adjust and relible but the 61 is a weak engine for its size and expensive. Thunder Tiger are a good engine and a fine choice but the best engine (imo) for this size is to go the the Tower Hobbies and pay $10.00 more than the 61 size and get the Tower Hobbies 75. Fantastic engine in this size regardless of the price. It takes a few more tanks to break in than the OS but its worth it! [8D]