This is a tuned pipe adaptor (also called an exhaust manifold), which is used to adapt a tuned pipe to an engine. This adaptor is a piece of metal tubing that turns 90 degrees towards the rear of the engine. At the end of this adaptor you will install the piece of silicone tubing (called a tuned pipe coupler, one is INCLUDED with this adaptor), and use tie-wraps (also INCLUDED) to keep the silicone from slipping. The tuned pipe will fit into the silicone tubing. The pipe is "tuned" by shortening or lengthening the distance the tuned pipe fits into the exhaust adaptor until the engine reaches maximum power and RPM. This adaptor measures 3-1/8" from the centerline of the output pipe to the outside of the base where it screws onto the engine. If an adaptor is needed that will be closer to the cowl (shorter radius), Mac"s makes two, MACG2861 and MACG2860. . This can be used with any of the following engines: O.S. .61 SF series . 9/1/92 JBN *8)