Final Performance Thought - Hot Bike Magazine

Whenever a long-duration cam is installed, the effect of increasing the compression ratio is of much greater importance, especially at low rpm. The cam's intake valve closing should be matched to the mechanical compression ratio to achieve optimized corrected compression and optimized performance. At low rpm, a late-closing intake reduces cylinder fill and torque. However, torque lost at low rpm can be regained (at least partially) by increasing the engine's mechanical compression ratio. This will allow the corrected compression ratio to maintain a predetermined level.

Compression ratio is another key optimizing variable. The corrected compression ratio (not to be confused with mechanical compression ratio and also called static compression) is a mathematically calculated number based on cylinder displacement and intake valve closing. It will always be a lower value than the mechanical compression ratio. A corrected compression ratio of 9:1 or a tad higher, depending on engine optimization, is roughly the maximum achievable on a pump-gas engine without encountering detonation. Keep in mind, however, that bike weight, gearing, combustion chamber design, rod length, ignition timing and ambient temperatures are some of the variables determining the maximum corrected compression achievable before encountering detonation.

Final Thoughts
When designing and building an engine to satisfy predefined performance objectives, the relationship between horsepower and torque is one of the most significant concepts to understand. Keep in mind that everything is a tradeoff; so make decisions wisely. Although all engines make torque, it is where the engine makes torque that will determine whether it is considered a "torque" or "horsepower" engine. Before buying costly parts, determine which type of engine your application and riding style need, then strive to build a "happy" engine by choosing performance components that are compatible and in harmony with one another. Knowledgeable engine builders maximize torque in the most important range of the rpm band and do not get overly concerned with horsepower.

The following equations are used for calculating horsepower and torque: