The Evolution Big Twin is the hero of the engine line up. It was this new design for 1984 which saved Harley Davidson from financial disaster. There are thousands of Evo enthusiasts who have done millions of miles on this very simple but effectively designed motor. The problem with the Evo is that it is very limited on compression which manifests itself as low power. A stock 80 cubic inch Evo puts out around 65 ft/lbs of torque and about 55 HP depending on the intake and exhaust characteristics. The cylinder heads have big ports and big exhaust valves which flow more air than its replacement engine, the Twin Cam. The combustion chamber design was advanced for its time and is a great improvement on what went before. The head castings respond well to minor port work and a larger 1.9 inch intake valve which when coupled with a performance cam can produce a great improvement in torque and horsepower. I’ve put some packages together which deliver a cost effective boost in performance.