Harley-Davidson
Engine Development and Modification
Performance and Technical information on modifying engines for Harley-Davidson motorcycles.

Looking for high performance engine specifications for your Harley-Davidson motorcycle? Need to know what high performance equipment provides the best performance at the lowest costs for your H-D. Here you can look at performance modifications with the dyno runs of many different engine combinations, so you can pick your own equipment, horsepower rating and dollars to spend. An incremental approach to engine development has provided some good results on many engines. Find out what combination of carburetor, camshaft, exhaust systems, ignition systems, head work, pistons and the other high performance components work well. There are tests of some equipment that did not work well. Know what works and what does not. Compare the results of your current bike to those seen here. Are you getting the performance you paid for?

If you have had success in your engine development program, send a picture of the bike and your performance results (dyno sheets or time slips) to the V-Twin Café for publication. The V-Twin Café is always looking for good articles on motorcycle performance work. If you write performance oriented articles, contact us.
Twin Cam
88 and 95
cubic inches		 Twin Cam Engines from Harley-Davidson have a good design and some nice upgrades available from the local Dealer including a 95 cubic inch big bore kit. What can you expect from this engine? Here are some engine configurations that have been tested.
45 to 50 HP Stock Evolution Engines are the starting point for all the modifications. The only way to validate what the performance gain was for any change is to have dyno runs before and after. These are the before runs of several bikes.
55 to 65 HP

Up to $750

 Stage One Evolution Harley-Davidson engines involve no internal changes made to the engine. All modifications are made by changing 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 65 horsepower at the rear wheel of a late model 80 CID Harley-Davidson big twin Evolution engine.

If you want to build your own Stage 1 engine, here are the parts used to create a 64 HP engine.
60 to 80 HP

Up to $1,500

 Stage Two Evolution Harley-Davidson engines involve any stage one changes plus changes to some internal "bolt-on" engine components. These "bolt-on" 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.

If you want to build your own Stage 2 engine, here are the parts used to create a 74 HP engine.
70 to 120 HP

$2,000+

 Stage Three Evolution Harley-Davidson engines involve any change to any component in the engine. These modifications should only be performed by experienced mechanics with knowledge of performance modifications and engine "blue printing". Special tools are required to perform stage three modifications. V-Twin Café will limit its Stage Three engine information to those combinations that are mostly streetable.
These modifications will provide from 80 to 120 horsepower at the rear wheel of a late model 80 CID Harley-Davidson big twin Evolution engine.

If you want to build your own Stage 3 engine, here are the part used to create an 82 HP engine that can be assembled over a weekend.
120 HP and more

$5,000+

 Stage Four Harley-Davidson engines are "anything goes". If it can be stuffed into a motorcycle chassis, it is worth trying. Time, expert knowledge, special tools and lots of money are required to build stage four engines. The ability to run on the street is not a criteria when designing these engines. These are all out race engines, designed for drag racing and other forms of competition.
These modifications can provide 120+ horsepower at the rear wheel of a late model 80 CID Harley-Davidson motorcycle. For these engines, the horsepower is only limited by the available money and engineering skills.
Shovelhead Engines The Shovelhead engine has been around for a long time. While the combustion chamber design is not as good as the Twin Cam and Evolution designs, there is still good power potential available in these engines. A good Shovel engine should make about 10% less power than a comparable Evo. This means your 80 CID Shovel can make 70-80 horsepower without to much trouble.
The Horsepower Gallery provides an extensive list of bikes , the power they produced and the major engine components. This list covers Evolution, Twin Cam 88/95 and Shovelhead engines.