Rocker arm ratios

by Sleddogg Tue May 21, 2013 6:19 pm

There is a lot of talk on many forums and rocker arm manufacturers websites about the inaccuracy of older rocker arms in reference to the ratio. Also, there are claims that new, modern manufacturing processes are more accurate resulting in a truer ratio on the rocker arm. I wonder if this applies to stock replacement rockers (sealed power, melling, etc) or only on the high dollar setups from Comp Cams and others. A stock replacement set of rockers from sealed power for my Pontiac run about $82.00 or so, while a roller tip set from Comp sits about $170.00. Something tells me that the more performance oriented manufactures probably are more sticklers on accurate ratio than the stock replacement parts.

Anybody know how to measure a rocker arm for accurate ratio?

by Limey SE Tue May 21, 2013 7:13 pm

The ratio of a rocker arm refers to the amount of movement on the valve side of the rocker arm in comparison to the pushrod side. A 1.5:1 rocker arm will move a valve 1.5 times the lift of the cam, assuming all things are in proper working order. If your cam has a lift of .4 inches, multiply by 1.5 to get .6 inches of actual valve movement. With the same cam lift of .4 inches: If you do the math on a set of 1.6:1 rocker arms: Multiply 1.6 x .4 inches of cam lift. You get .64 inches of actual valve movement. Essentially, changing to a larger ratio rocker arm is the same as increasing the lift of your cam the same amount. Opening both valves further usually is a benefit in the power department as your engine is capable of moving more air and exhaust through it.

by Sleddogg Tue May 21, 2013 8:09 pm

Makes sense, and appreciated. I guess what I am getting at, is there any formula or reference for measuring or obtaining the ratio of a particular rocker off the car? I hear a lot about stock rockers being out of spec (ratio being advertised at 1.5, but actually being 1.43 or something). Also inconsistencies during manufacturing (sixteen rockers having sixteen differences in ratios ratios etc). I guess I am just being a cheap a@@ and trying to save some bread, and would like to run a new, consistent set of stock type rockers. Perhaps going roller tip will be the route I should take. Maybe I am splitting hairs...
cyclops

by bracketchev1221 Tue May 21, 2013 8:20 pm

The easiest way I know is to use a dial indicator on the tip of the rocker. You know what the advertised no lash lift number is. This is what you should see at the dial. As far as ratio, yes they sometimes can be all over the map. But I don't think that requires roller tips. A good name brand stock rocker is all you need. As far as I am concerned the roller tips offer no benefit. The friction is mostly at the pivot point, not the tip.

by Sleddogg Tue May 21, 2013 9:49 pm

I found a set of stock replacement rockers from Comp. Same prices as what I could get Sealed Power from locally. Had good luck from Comp before, I think I will give these a shot.

I am having a set of heads redone here shortly and am collecting my parts. Trying to stay on the reasonable side where I can.

Thanks for the replies.

by pila Tue May 21, 2013 10:24 pm

When Comp Cams was working on a low priced roller tip rocker, they claimed that they had a bushel of the stock Chevy rocker arms to test for ratio.
Their result showed that the stock Chevy stamped-out rockers varied all over the place, like from 1.4 to close to 1.6.
They produced the 1.52 ratio roller tipped type, and a 1.6 ratio, which is priced low enough for folks to but in place of stock types.
I use those in stock type rebuilds, and the oldest set I have is in my Malibu, from back when they first came on the market. No complaints about them.

by Sleddogg Wed May 22, 2013 11:34 am

That was my concern if some of the stock replacement oem-style rockers manufactured by typical parts store companies had the same inconsistency. My friend at one of the local parts houses has no problems with me going through the rockers he has in stock to check, but didn't know how to do it with just a rocker arm in my hand. But as it turns out, it's just as affordable to get them from Comp...I am assuming that they have a little more stringent tolerances than some of the oem replacements. Of course, I hate to assume Smile

by pila Wed May 22, 2013 4:29 pm

They are not stampings, like the OEM types, but are a sort of investment casting from what I remember of the details.
Here's the Comp rockers in my Caddy 500 engine in my '75 Elco...
Rocker arm ratios P1010981_zpsb781655e

by 77mali Wed May 22, 2013 5:42 pm

The Comp Cams Magnum rockers are great quality. I have them as well in the 1.52 version. It's not quite as good as having a full roller Cam set up but you do get the benefit of less wear on the valve spring assemblies.

by bracketchev1221 Wed May 22, 2013 8:31 pm

http://www.summitracing.com/parts/cca-1251-16/applications/make/pontiac?prefilter=1

by Sleddogg Thu May 23, 2013 1:38 am

Thanks for the link!

I was looking at those just the other day Smile

by dragons_lair59 Thu May 23, 2013 9:10 am

I had proform roller rockers in my old Monte and those had been in a couple circle track motors first and I had no issues and the price is very reasonable
http://m.summitracing.com/parts/pro-66907
And that's full rollers

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