Rocker Arm Ratio

[Fred M.]

Can someone please tell me the standard rocker arm ratio correct for #461 heads (dtd Sep '63) for a '64 327/365 car? Additionally, please list the pros/cons of using different ratios. As always, thanks in advance.

[Duke W.]

Re: Rocker Arm Ratio

The "design" rocker arm ratio for all small blocks is 1.5:1.

The actual rocker ratio according to my measurements is about 1.37:1 at the lash point and about 1.44:1 at peak lift for OE cams.

Higher ratio rocker arms effectively yield a "bigger cam" due to more lift, but require stiffer valve springs to due increased dynamics at the valve.

Published tests that have been referenced here show only very marginal improvements in output with aftermarket higher ratio rockers arms - maybe 2 percent. There are much more cost effective ways of improving engine performance than aftermarket high ratio rockers.

OE/OE equivalent cam lobes, springs, pushrods, and rockers have Rock of Gibralter reliability and durability, and are all I recommend unless we're talking about a serious vintage racing engine.

Duke

[Tom L.]

Re: Rocker Arm Ratio

Back in the early 90's I races street stock cars on an oval track. Rules were pretty strict in this class. We built a a motor and tried higher ratio rockers... DISASTER. No major failures but we used them for 3 weeks and went back to stock rockers.

There 2 types of failures in a rather short amount of runnning time, either the pushrod went right through the rocker tip or the upper prortion of the rocker seperated from the lower part that the ball held in place. We were turning the motors up to about 7200rpm. Not sure if a street engine would have these problems. Good luck!!

[Clem Z.]

Re: Rocker Arm Ratio

Back in the early 90's I races street stock cars on an oval track. Rules were pretty strict in this class. We built a a motor and tried higher ratio rockers... DISASTER. No major failures but we used them for 3 weeks and went back to stock rockers.

There 2 types of failures in a rather short amount of runnning time, either the pushrod went right through the rocker tip or the upper prortion of the rocker seperated from the lower part that the ball held in place. We were turning the motors up to about 7200rpm. Not sure if a street engine would have these problems. Good luck!!

seen the same problem back then using stamped steel rocker arms because the manufacturer had cut the stamping process from 7 steps to 4 steps and this cause metallurgy problems.

[Tom L.]

Re: Rocker Arm Ratio

I remember our engine builder making similar complaints. We tried 3 manufacturers, including GM, in 3 weeks and abandioned the higher ratio rockers. Never had another problem.