[PAUL K]

I disagree that rocker arms are intentionally made with a higher than advertised ratio to account for deflection or any other reason. It would screw a lot of conscientious builders if that were the case. As mentioned in an earlier post a set of 1.6 rockers were chosen because of minimal retainer to seal clearance. With the trend today of hi-lift cams being used in street cars you would have a lot of excessive guide wear, coil bind and smashed valve seals if rocker arms weren't correct ratio or usually a little less.

It's not as simple for the average fellow to check ratio as most would think. First the pushrod length needs to be optimized for each rocker arm because that will affect the net lift. Then one must decide whether to check with the valve spring in place or a test spring. A high RPM race engine will give up .030 or more lift checking this during the assembly if it's checked with a valve spring in place.

My guess is most of the "extra" ratio comes from second hand information that stems from the ratio not being checked properly by the originator of the rumor. I have checked many rocker arms for ratio and how far the rocker moves the pushrod towards or away from the rocker studs.... I do the later due to my dislike for grinding the head for pushrod clearance. I have found very few that have more ratio than advertised. I have found that some can be "tricked" to give more valve action by adjusting the pushrod length. But then one must decide between added valve open time or optimized geometry.

I have never seen a high end rocker shaft have anything but the advertised ratio. For many reason the shafts are dead nutz on, but if any rocker arm builder was going to add extra lift "for a reason" , the most logical being valvetrain deflection, one would think it would be the guys building rocker arms for a 9,000 rpm application using 1500 lbs. of spring pressure.

The only rocker arms I have found that consistantly check out higher than advertised is the Harland Sharp 1.65 and the Comp Cams 1.5 (which used to be advertised at 1.52) Pontiac rocker arms. I believe HS now makes four versions of the 1.65 and only one consistently measures close to 1.7. I asked Randy Sharpe directly about this and he had no idea as to why this is and wasn't aware of it. He said it definetly wasn't done for a specific reason, such as deflection. That might be why their newer 1.65 rockers measure closer to the advertised number.

FWIW


PS..... It'd be nice if a manufacturer would perfect an adjustable ratio rocker arm like Crane offered many years ago.