Skunk2 Racing Cams & Cam Gears - The Science Of Cam Gears How, What, And Why

A big portion of this is done through the adjustment of overlap. Overlap is the portion of time during which the intake and exhaust valves are simultaneously open. It is during the sliver of time that overlap occurs that attention must be paid, because it is here that power, gas mileage, emissions, and drivability are all affected. As the exhaust gas rushes out the open exhaust valves, the vacuum its quick exit creates helps to draw in some of the intake mixture through the open intake valves. A balance must be struck though, taking care of managing the movement of gases in order to avoid an overly lean or rich situation.

By advancing or retarding intake and exhaust cam timing, we can adjust overlap and its resulting effects on power and torque. In general, retarding an exhaust cam or advancing an intake cam will increase overlap and advancing an exhaust cam or retarding an intake cam will decrease overlap. The amount of overlap and the proper settings each cam gear will need to be set to depends on each car, but be aware, it is during the overlap portion that interference can occur. Possessing an inverse relationship, by decreasing overlap there is an increase in both valve to valve and piston to valve clearance, while increasing overlap will decrease both.

So, needless to say, try not to advance your intake or retard your exhaust too much. Both will decrease your valuable clearances and run closer to the risk of engine damage. Horsepower is good, but pistons hitting valves is definitely not. The best settings to achieve peak power and reliability are different for every car, but the recommended way to find out which settings are for you is on the dyno. If you have no knowledge of how your engine will respond, you'll have to try various combinations of advancing and retarding the intake and exhaust gears and note the results on your powerband. When you are satisfied with those results, you can finally fine-tune your powerband throughout the entire RPM range by adjusting both the same amount. In general, advancing timing for both intake and exhaust will increase low-end power and decrease high-end power, while retarding timing for both will shift the power to the top-end.

Also, cam gears themselves are not all made equal. Due to their adjustable nature, many cam gears on the market make use of small bolts to hold their settings in place after installation. Cheaper models have bolts with a tendency to slip, leading to disastrous results. Attention must also be paid to the machining of the cam gear teeth, lower quality machining of brittle metals can lead to gears with poor grip that prematurely wear both the timing belt and their own teeth. Skunk2 CNC machines all of their gears from billet aluminum and utilizes a six-bolt design to ensure the gear will never slip out of place. Their Pro Series cam gears also possess the benefit of being some of the lightest on the market, which brings to mind another good point. Anytime you are able to free up some unwanted reciprocating mass in the valvetrain, you and your motor will be very happy.

By Joey Leh

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