2016 Duration Rule Change
HOW WILL THE 2016 CAM DURATION RULE AFFECT ME?
We get this question on a daily basis, "How will the new 2016 cam duration rules affect me?" Cam Duration is the number of crank degrees between when a camshaft opens the valve and when it allows the valve to close. Under normal circumstances bigger duration would be better. However, when you throw the 10.8lb spring in the mix, everything changes. OHV Engines take advantage of the controlled valve float just like the old flat heads did back in the day. The standard CL2 is about 1 degree below the maximum allowed duration. It will usually rev to 6500-6600 maximum RPM in the average unrestricted engine. The valves begin to float between 5500-6000 RPM, thus we generally see horsepower spike, or peak, in this RPM range. The CL2 will completely float the valves beyond the capacity of the 10.8lb spring around the 6500-6600 RPM range.
IN A SPORT WHERE LESS OF ANYTHING IS USUALLY A BAD THING, WHY IS LESS DURATION BETTER?
The hot topic amongst racers now is lower duration camshafts. By lowering the duration at .200 lift the camshaft is now much smoother across the nose or maximum lift surface of the cam.
The figure shows a lift comparison of a CL2 (Red) vs. a cam with lower duration. The lift of the low duration cam is smoother across the nose.
The smoother nose allows the cam to rev into the 6800-7000 RPM range before completely floating the valves beyond the capability of the 10.8lb springs. This is how a cam with less duration is able to turn more RPM with the weak 10.8lb springs.
THE RPM GAIN DOESN"T COME WITHOUT A COST
Since we no longer float the valves in 5500-6000 RPM band, we do lose a little bit of peak horsepower in order to gain horsepower in the upper RPM band.
WHICH WAY IS BETTER?
It is the preference of the engine builder as to which setup works best for their package.
HOW DOES THIS AFFECT THE RACER IN 2016?
The new camshaft ruling in AKRA of +2/-5 degrees takes effect on 3/1/16. This will eliminate many of the lower duration grinds that are currently being used. However, the CL1, Cl1-I, CL2 and CL2-R2 will remain legal in 2016. We are releasing the CL3 , a new grind for 2016, that will take advantage of the new rules. It will show more in the upper RPM band than our current grinds. However, keep in mind we will lose a small amount at our peak horsepower range.
It is our intention to shed light on the new rule and how it affects our customers. If you ever have questions about any of our products, please give us a call. You can also check us out on Facebook, Twitter, Instagram, LinkedIn, and Google+. We have in-house techs, engine builders, camshaft specialists, and 30+ years of experience in kart racing. We appreciate your continued support of DynoCams.