Rocker Arm Ratio - Power Multipliers

Rocker Arm Ratios Can Add Power

Mike Petralia Feb 1, 2002 0 Comment(s)
Sucp_0202_16_z Rocker_arm_ratio Diagram 1/8

The Hot Rockers system works by shifting the fulcrum pivot of the rocker arms as you drive. All rockers will shift together, so you cannot run different ratios on the intake and exhaust. The four-position fulcrum provides ratios from 1.1:1 up to 1.75:1 (higher or lower ratios can also be specified). An ECM shifts the ratios at user-defined rpm points via an electric motor mounted on the valve covers.

Piston-To-Valve (Ptv) Clearance
Increasing the rocker ratio adds lift that could cause the valves to tap the pistons if they were close before. Since an increase from a 1.5- to a 1.6-ratio only nets about 0.030 inch total extra valve lift, and total valve lift is not what you're checking when you look for PTV clearance, this may not be an issue. A minimum of 0.100-inch-intake and 0.080-inch-exhaust clearance is recommended.

Retainer-To-Seal Clearance
With your rocker arms properly lashed, check to make sure there's about 0.030 inch clearance between the spring retainer and valve seal at max lift. This check is easiest to do with checking springs installed. You can also measure the total clearance with the valve closed and subtract your total lift to calculate the clearance. Remember to calculate lift using the new ratio.

Valve Spring Coil Bind
This only requires you to find your valve spring installed height and subtract the coil bind height to find out how much lift your springs can take. It's best to keep a minimum of 0.030 inch between a few coils if you want your springs to live.

Pushrod-To-Head Clearance
Increasing the ratio of a rocker arm could make the pushrods hit the head or guideplate. There's really no way to check this without installing the new rocker arms and cycling the engine by hand. Carefully check under and around the guideplate to make sure the pushrod doesn't hit.

Rocker Arm To Retainer Clearance
If you're installing big-diameter springs, make sure that your rocker arms don't hit the retainers. To cure this you can install lash caps on the valve stem tips. There are also many different-height valve locks to try, but that will affect your spring's installed height. Also, not all retainers are created equal, and you might be able to find a different set that will clear.

Sources

Crane Cams
Daytona Beach, FL 32117
866-388-5120
http://www.cranecams.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
T&D Machine Products
Carson City, NV
775-884-2292
http://www.tdmach.com
Crower Cams
San Diego, CA 92154
619-661-6477
http://www.crower.com
Erson Cams
Carson City, NV 89706
800-753-2386
pbm-erson
Iskenderian Racing Cams
Gardena, CA 90247-9990
Jesel Inc.
Lakewood, NJ 08701
Everoc Industries (Hot Rockers)
Frisco, TX 75035

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