V8 GT pilot
Join Date: Sep 2003
Location: At the wreckers for ESP parts
Re: .525 lift too much?
The other thing that people forget is that rollers actually have a higher reciprocating mass than standard rockers. Rollers don't "give" you any extra power, they are just more reliable within the power band that you have. They are designed for continuous high rev, high load applications as they do not fatigue or flex like standard rockers can.
I've got YT Rockers on my car and did notice that they quietened the valve train down a bit, but there certainly weren't any other noticeable benefits on the DYNO or otherwise. In fact, they can actually place greater stress on pushrods because this can become the gretaest area for flex and stress absorption.................so I had to go Moly one piece just to make sure. Rollers are also less tolerant to valvetrain geometry variances. You need to ensure that the valve stem tip to roller tip is spot on and that you choose the correct Rocker ratio as this can vary your cam lift. As per the guys from Yella Terra :
Rockers increase the lift of the cam by having unequal lengths from the pushrod cup or adjusting screw to the fulcrum and from the fulcrum to the tip of the valve.
Most rockers have a theoretical ratio of 1.5 to 1.7:1 that is the rocker increases valve lift by 1.5 or 1.7 times the cam lobe lift.
If your cam has a lift of .375" with 1.5:1 rockers, the lift at the would be .563" and .600" with a 1.6:1 rocker. Remember with solid lifter cams, valve clearance must be deducted from theoretical available lift.
Rocker arm ratio changes are frequently used to test the benefit of a higher lift of the valves without resorting to the more substantial camshaft changes.
Competition engine builders frequently experiment with changing inlet or exhaust and possibly both rockers, to establish if power gains are possible with different ratios.
An increased ratio will open the valve faster, lift it higher and close it faster, but won't effect the cam timing. The increased acceleration and deceleration of the valve from a higher ratio could lead to valve float occurring at a lower rpm.