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Rocker Arm Ratio - Power Multipliers

Rocker Arm Ratios Can Add Power

By Mike Petralia

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
COMP Cams Everoc Industries (Hot Rockers)
7955 Maiden Ln.
Frisco
TX  75035
Crane Cams
530 Fentress Blvd.
Daytona Beach
FL  32114
3-86/-252-1151
N/A
www.cranecams.com
Iskenderian Racing Cams
16020 South Broadway,
Dept. MMFF
Gardena
CA  90247-9990
Crower Cams
San Diego
CA
619-661-6477
www.crower.com
Jesel Inc.
1985 Cedarbridge Avenue
Dept. MMFF
Lakewood
NJ  08701
Erson Cams
550 Mallory Way
Carson City
NV  89701
775-882-6600
www.mrgasket.com/erson.htm
T&D Machine Products
Carson City
NV
7-75/-884-2292
www.tdmach.com
By Mike Petralia
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