Mid-Range - High-Performance Camshafts what it's all About

Most motorcyclists who bought the obvious aftermarket engine performance replacements like sportier air-filters and exhaust-systems believe that the next step to increasing performance is to replace the camshaft by a high-performance cams.

High-performance cams, ported heads, larger carburetors, or modified injection systems, and wide-open exhaust system add little useful power below 4,500 rpm. They can and often reduce power below 4,000 rpm. This may go against most of what you may have heard about cams, pipes, air-filters and so on. But what I say has been verified many times on dynamometers and on the street: Displacement and compression are your best friends when it comes to getting more power between 2,000 and 5,000 rpm from you motorcycle.

Mild Camshafts Work Best

Useful gains are possible in mid-rpm power without changing the camshaft. So let's look at what sort of cam design you might consider if you do choose to install new ones.

Most stock cams are excellent in design and execution, bringing quiet, reliable operation and good performance in normal use. However, their design is otherwise compromised by the need to meet Thai emission standards. These considerations, and more, result in camshaft design that produce moderate power.

Only the smallest design changes are needed to meet our goal of increased mid-rpm power. Specifically, the intake valve is closed sooner to seal the chamber early in the compression stroke and thus raise the pressure in the chamber at the time of ignition. The sooner the intake valve is closed, the lower the rpm at which useful power is produced.

Most stock camshafts - and there have been many variations over the years - close the intake valves between 35 and 39 degrees after top dead center. This means that the engine begins to do its best work near 4,000 to 5,000 rpm. If the intake cam closes the valve at 30 degrees ATDC, the responsive, useful power can start much lower.

Most aftermarket camshafts close the intake valves later, in most cases much later, than stock. They are almost all designed to increase power above 7,000 to 8,000 rpm and their timing reflects that. For instance, a cam that closes the intake valves at, say, 40 degrees will not start doing its best work until 7,000 rpm. No matter what claims their makers may make... well, you just can't fool Mother Nature. Stay away from any camshaft that closes the valves later then stock - if you're after torque, that is.
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