Harley Davidson Engine Modification Manual

Following Modifikation Manual Engine applies for Harley Davidson motorcycle. There are 4 stages of modification explained and described in this manual. Stage 1 modifications are made by bolt-on changes or modifications to external components on the engine. These components include air cleaners, carburetors, exhaust systems and ignition systems. No special tools or training is required to perform Stage One modifications. These modifications will provide from 55 to 66 horsepower at the rear wheel of a late model 80 CID Harley-Davidson big twin Evolution engine.

Stage 2 Harley-Davidson engines modification involve Stage 1 changes plus changes to some internal “bolt-in” engine components. These “bolt-in” modifications include camshafts and milling of the heads to increase compression. Some special tools and knowledge of engines is required to perform stage two modifications. These modifications will provide from 60 to 80 horsepower at the rear wheel of a late model 80 CID Harley-Davidson big twin Evolution engine, depending upon the condition of the engine and the components used.