This is the Big Block Conversion Kit from Traxxas for the Traxxas Revo monster trucks. This conversion kit gives Revo owners the option of installing various .21-.28 size pilot shaft big block engines in their monster truck. The conversion kit also includes the forward only conversion kit as well as the big block engine mounting hardware. The following items are included: - Forward only conversion kit - TRA5394X - Universal engine mount - Manifold with gasket and spring - Flywheel and clutch nut - Forward only shaft - Miscellaneous hardware required for installation The following engines are known to work with this installation kit without modifications: O.S. .21 VZ-B, Team Orion Wasp .28 and the Dynamite Mach .26. The following engines are known to work with modification work on the engine mounting assembly: Nova Rossi 528, Nova Rossi .21 P5, Picco .21 Maxx, Sirio S23TX, Sirio S27, and Team Orion Wasp .26, OFNA Picco .27 (non pull start only!). The following engines are known to NOT work with this conversion kit: Thunder Tiger Magnum Pro 21, Associated Pro 21R, O.S. .21 RG and O.S. .21 RZ. For a list of what is required to install the above mentioned engines and to download installation instructions visit the following web address: http://www.traxxas.com/products/news/big-block.htm