Engine 101: Adjustable Cam Gear

Have you ever wondered what a vernier adjustable cam sprocket is? Or why you might need one? Or two for that matter? The timing of the intake and exhaust valve opening and closing events can have a dramatic effect on the amount of torque an engine makes, and where in the rev range peak torque is achieved. Vernier adjustable cam gears allow the cams to be advanced or retarded in relation to the crankshaft, or by adjusting just one camshaft, the amount of overlap (time when the intake and exhaust valves are open simultaneously) can also be altered. The aim is to adjust the cam timing in order to optimize cylinder filling, since the more air we can get into the cylinder, the more power and torque we can make. The trouble is that this is a compromise….what might be perfect at low rpm will almost certainly compromise high rpm performance and vice versa. As a general guideline at low rpm when the air velocity is low, opening the valves earlier in the engine cycle generally improves cylinder filling. This is referred to as advanced cam timing. At high rpm however we can take advantage of the high air speed and hence inertia of the intake charge by opening and closing the valves later which is referred to as retarded cam timing. Vernier cam gears allow the cam timing to be accurately adjusted and the optimal cam timing for your usage can be found. Of course if you want to optimize engine performance throughout the rev range you’re going to need continuously variable cam control but that’s a topic for another post.

If you want to learn more about EFI tuning, check High Performance Academy EFI Fundamentals course.

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