because the tip of the rocker arm moves on an arc.

Brad Haak had some really good examples, actual measurements, and CAD drawings in a detailed post about that very thing.

If you search through his posts you should be able to find it.

I wrote a couple of books

Years ago Racer Brown recommended going through a set of stock rockers and selecting those that had equivalent lifts. I have done this multiple times and yes, the ratio of a stock Mopar rocker is all over the map.

not to hijack here, but i've got a set of crane golds on my go to driver and was thinking about changing them out; over 20,000 miles on them. i thought i might have a geometry issue with new stuff seeing how i can't buy old stuff but that pic dwayne put up,.... . i thought things might be goofy but that's beyond goofy for me. i don't use a fast rate cam or big pressures but it looks like it's all head specific. i would have thought there might be some overlap as far as usage goes but maybe not. the deal with those prw rockers seems outrageous. were they the comp cams clones or the alum?

I checked the actual lobe back when I got the cam. I also have, in the past, checked the actual valve lift at zero lash. The Crane's were giving me pretty much the real deal. I think it was out by .005" from the theoretical .613", which can be attributed to arc and some deflection. I had killer valve springs.

Thanks Dwayne, I'll look into it...wb

The rockers aren’t marked for ratio, correct?

My guess is....... they’re 1.5’s in a 1.6 box.

.575 lift with a 1.5 is .383 lobe lift.
You getting .513 with .020 lash, which would put the number at .533 gross lift.
533/383 = 1.39.

I find it hard to believe they’d be that far off(1.6 > 1.39).

1.5 > 1.39 would be bad enough.

The rockers themselves are marked 1.6..

Pictures !!! Top and side.

Interesting. The ones that were on a motor that was just on the dyno here had no markings.
The two that were checked measured in the 1.45 range.

This isn’t doing much to make me change my mind about not using Chinese rockers.

I've measure a bunch of different brand BB Mopar adjustable rocker arms, stock Ductile iron Max Wedges, stock Street Hemi ductile iron rockers from many different motors, Isky, Cranes and Erson brand ductile iron rocker arms as well as several different brands of aluminum rocker arms like Harland sharp, both early and later made, and several sets of T&D single shaft sets, none of them were dead nuts on the ratio on the complete sets sent to me from the factories
I use to send the ductile iron sets to a company in northern, CA for blue printing and making them accurate, after checking several different sets I had done by them I stopped doing that
i have not yet check a complete set of Jesel paired shaft aluminum or steel rocker arms, that is next

Fair point. I'll probably find out on Monday what the manufacturer has to say.

How many of the eight common dialects spoken in China do you know?

I think one thing many take for granted is that the rocker ratio will yield the equivalent ratio of valve lift with every cam. However, the rocker ratio is exactly that - its the ratio of the distance from the center of the shaft to the center of the pushrod versus the distance from the shaft to the center of the valve contact point. Given the stock geometry of the shaft position, valve height and rocker design, a stockish .300 cam will yield .40 valve lift because its all designed to. But if you throw in a .400 lift cam with no changes to the shaft or valve length, you should not expect .600 lift. There are a few other factors that will affect the valve lift when you slap in a cam with double the stock lift. Without changing the shaft height or valve length, the rocker will be at a much great angle half way though the lift with the bigger cam. This results in a much lower lift ratio in the second half of the valve lift. It works similar to a piston - the fastest travel is is halfway in the bore but at the top or bottom its moving slower because of the crank angle.

That’s all fine and dandy, but it sounds like the Crane 1.6’s yielded .080” more valve lift than the PRW’s with the same cam(lobe lift).

I know which scenario I’d rather have in my engine.

My guess is that someone at the PRW factory stamped a set of 1.50 rockers with the 1.60 ID and then they got boxed and sold as 1.60 rockers. PRW gave me a set of their steel rocker arms when they first came out for a magazine article, but the rockers were a timebomb so I never used them. The rockers had ribs around the roller tip that were too big. The ribs hit the valve lock before the roller hit the valve stem so the load was all being carried by the valve lock. I never even started the engine when I saw that. Just boxed up the rocker arms and sent them back and never included them in the article. I assume they fixed this design flaw but I haven't looked at a set since.

The old unbushed will-seize-on-the-shaft CAT stainless rockers were also like that.

There is obviously no testing done on that stuff, or input from builders familiar with the platform for that matter.

I didn’t see where the OP mentioned if this is a BB or SB.

On the SB, there is a definite loss of effective ratio(as measured at the valve) from the 59* lifter bank angle and the pushrod angle.

I had the same issue with the ones that 440Source marketed briefly. Put them in the mill and fixed them.

Rocker body wasn't spot faced for the jam nut and when you tightened it down, it broke the adjuster. Source replaced them with new and improved but still had to trim the roller end.

Then discovered the adjusters were made of glass. Replaced them with Comp adjusters and thought we had beat them into submission...

Some time later, I had a valve cover gasket leak that was a big blessing in disguise. Pulled the cover and found one side of the roller end was broken on one rocker and when I took them off the engine discovered the rollers were loose enough on their axles that you could hear them rattle from across the shop when you shook them...

Shoulda just bought the Comp Magnums...

Kevin

small block PRW rocker i recently bought.
no lock interference on this setup.