Sold Out Compare Quick view O.S. PowerBoost Muffler Pipe 91HZ Series T-REX O.S. MSRP: $299.99 Now: $199.99 Was: .91 size Powerboost Pipe from O.S. Engines.FEATURES: Fits O.S. Speed 91HZ-R 3D and 91HZ series engines Developed exclusively for 3D flights with 90 size... 72145000 MSRP: $299.99 Now: $199.99 Was: Sold Out Compare Quick view