you might as well pop the head off and check for shim stack, if its got more than one in , i wouldnt be afraid to run 20/20 fuel in it, the 128's and 148's will handle 6 volts just fine. they are if my memory serves me about 45 ounces of torque., i flew a rossi powered kaos hundreds of flights on a five cell pack with no problems what so ever.