Med:

Regrinding the cam is one possibility to increase the duration, another and often easier method is installing mushroomed tappets. By having the contact end of the tappet a larger diameter the valve lifts at an earlier point in the cam's rotation, and it closes later.

Before you start any modifications, though, the model 4s engines all have pretty hot cams to start with, making them "Racier" tends to disrupt the idle.

A goos example is the FA-120 Saito compared to the FA-120S engine. More power with the "S" but not as good an idle. The "S" uses a cam only slightly hotter, but it has mushroom tappets making it effectively a "Race" cam compared to the "Mild street" in the normal engine.

Pisture is the parts that are changed to accomodate the mushroom tappets, compared to the normal parts.

Bill.