RE: Viper 500
The Webra 55 turns an APC 9 X 10 @ 16,300 with a red Jett muffler on Wildcat 15/18. The engine that died had less one gallon though it. The other two have about 2 & 3 gallons on them and still strong, mounted on a standard and clipped wing Diamond Dust with the same prop size. You can run less nitro and see only a small rpm drop.