Roller-Rocker Ratio Test

Shown here from left to right are the three rocker-arm types we tested: a stock stamped 1.5:1 rocker, Comp Cams 1.5:1 Pro Magnum roller rocker, Comp Cams 1.6:1 Pro Magnum rocker, and a Comp 1.65:1 High Energy aluminum rocker.

Shown here from left to right are the three rocker-arm types we tested: a stock stamped 1.

Fast Facts
We prefer to adjust the rockers in the firing order of the motor using the Exhaust Opening, Intake Closing method (use EOIC as a shorthand memory aid). This method ensures that the lifter of the valve you're adjusting is on the basecircle of the cam when you set the lash. To begin, put all the rockers in place and tighten the nuts or Poly-Loks enough that the arms will open and close the valves as the motor is being turned over. Start with the No. 1 cylinder intake valve and turn the motor until the exhaust valve is just beginning to open. The intake rocker should be loose; if not, loosen the nut until you can move the arm. Make sure the pushrod is seated in its pocket on the arm and tighten down the nut slowly until you can no longer move the arm or turn the push rod. This is zero-lash. Tighten the nut 1/8- to 1/4-turn more, then tighten both the nut and poly-lock with an Allen wrench another 1/8- to 1/4-turn at the same time. Do this to all the intake side rockers. To adjust the exhaust sides, again go in the firing order, but allow the intake valves to close 1/2 to 3/4 of the way before you adjust the exhaust valve.

Math Anyone?
If you're not sure what the valve-lift numbers will be with a larger-ratio roller rocker, then get out the calculator as we fill you in. Take the intake/exhaust lift numbers from the cam catalog and choose one side to begin with. For example, the Comp Xtreme Energy 268H has 0.477-inch lift at the valve on the intake side. Since the 350 comes with a factory 1.5:1 ratio rocker arm, we take 0.477 and divide it by 1.5. This results in 0.318 inch, which is our lobe lift on the intake side. Next, take 0.318 and multiply it by the new arm ratio. With a 1.6:1 rocker, this gives us 0.508-inch valve lift at max lift, an increase of 0.031 inch. It doesn't sound like much, yet it was enough to show a sizeable gain, mainly because it increases the amount of time that the valves are open at higher lifts, allowing more air to flow through the heads. The valve will now see 0.500-inch lift twice during each combustion cycle (once as it opens and again after peak lift on the closing side). Do the same for the exhaust side and be sure to check for piston to valve clearance before making any radical change.