if you can work on the engines then you should. With some mods you can get 17,000 with a APC 9x8. open up the carb, exhuast port, might have to lower the sleeve, and might have to mess with the crank timing. now if you dont want to do that then a great option is to sell them and buy a newer super tiger 45 from tower and order a "black" jett muffler. this combo stock will spin a 9x8 APC prop 17,000. this will pull that plane around 130-140.