CLASS RACER FORUM - Rocker Arms---Does an official clarification exist

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Rocker Arms---Does an official clarification exist

I have been talking with some of you about the question of rocker arm ratio that has been hammered on several previous post that I do not want us to unpack again---SO---the burning question is----does an official published document exist from NHRA tech covering all possibilities and doubts concerning rocker arm ratio being factory stamped on rocker arms as shown in engine specifications for visual inspection regardless of how it checks ??? I hope I did not ask that incorrectly. I would like to thank Alan R. and others for talking to me about this, but is there anything in writing and if not why not ???

Re: Rocker Arms---Does an official clarification exist

NHRA rules require that a rocker arm used on a stocker motor(I assume that is what you need info on here) must maintain the OEM rocker arm ratio. If a cam checks out at ,let's say, .300" lift on the lobe and the max lift spec is .450, you need to maintain that rocker ratio spec EXACTLY. If the spec was .450", your cam shaft actually checked at,let's say,.325", that does not mean you can use a 1.55 or a 1.6 ratio rocker to compensate for the lack of lobe lift.If such a scenario developed in your motor,where lobe lift is a bit low, sometimes using a longer or shorter pushrod might enhance the rocker arm actual geometry enough to compensate for this. We had a discussion regarding pushrod length here a few years ago that was very entertaining to read, to say the least. Also, non-adjustable rocker arm assemblies, such as Mopars, would require an adjustable pushrod to correct any valve lash issues that may exist. Adjustable rocker arms, such as on any Chevrolet, would require a non adjustable pushrod. You can't have both in the same engine as per NHRA. If my 327 Chevy cam checked exactly as to lobe lift, and the rocker arm ACTUAL ratio was exact at 1.5 to 1, and valve lift was insufficient or excessive, the only way to correct this would be to use a different length pushrod.They check lobe lift and actual lift in tear down,then it's a matter of simple math to determine if the rocker arm ratio is in spec.I do not know of any official spec or official markings on any rocker arm regarding the ratio. If a rocker arm was close one way or another, then the only way to use it is through the different length pushrod trick. Why they are a little vague on this is a good question.

Re: Rocker Arms---Does an official clarification exist

Maybe an answer based in the fact that the rocker ratio is printed as part of the tech specs for every engine?

Re: Rocker Arms---Does an official clarification exist

I was always under the impression that lobe lift lost through bad geometry, or whatever, can be made up by extra lift at the cam lobe. Rocker ratio remains per spec and as long as gross lift at the valve remains per spec., it's legal.

The use of OEM shaft style non-adjustable rocker arms on Mopars shouldn't even be a consideration considering the lower than advertised ratio and lack of durability. Even aftermarket ductile iron Crane, Isky, etc. are "off" of spec. but can be corrected. Aluminum roller rockers should be checked to be sure.

Re: Rocker Arms---Does an official clarification exist

Quote:

Originally Posted by Greg Reimer 7376 (Post 450689)

NHRA rules require that a rocker arm used on a stocker motor(I assume that is what you need info on here) must maintain the OEM rocker arm ratio. If a cam checks out at ,let's say, .300" lift on the lobe and the max lift spec is .450, you need to maintain that rocker ratio spec EXACTLY. If the spec was .450", your cam shaft actually checked at,let's say,.325", that does not mean you can use a 1.55 or a 1.6 ratio rocker to compensate for the lack of lobe lift.If such a scenario developed in your motor,where lobe lift is a bit low, sometimes using a longer or shorter pushrod might enhance the rocker arm actual geometry enough to compensate for this. We had a discussion regarding pushrod length here a few years ago that was very entertaining to read, to say the least. Also, non-adjustable rocker arm assemblies, such as Mopars, would require an adjustable pushrod to correct any valve lash issues that may exist. Adjustable rocker arms, such as on any Chevrolet, would require a non adjustable Ypushrod. You can't have both in the same engine as per NHRA. If my 327 Chevy cam checked exactly as to lobe lift, and the rocker arm ACTUAL ratio was exact at 1.5 to 1, and valve lift was insufficient or excessive, the only way to correct this would be to use a different length pushrod.They check lobe lift and actual lift in tear down,then it's a matter of simple math to determine if the rocker arm ratio is in spec.I do not know of any official spec or official markings on any rocker arm regarding the ratio. If a rocker arm was close one way or another, then the only way to use it is through the different length pushrod trick. Why they are a little vague on this is a good question.

Let me clarify---Comp Cams has a factory 1.5 factory marked on rocker regarding ratio......is that important even though mathmatically incorrect ???

Re: Rocker Arms---Official Clarification

Today's email from Bruce Bachelder------

" AS LONG AS THE CAM LIFT, CHECKED WITH A SOLID LIFTER, DOES NOT EXCEED THE SPEC YOU ARE ALL SET "

SOUNDS PRETTY CLEAR TO ME, THE NUMBERS DONT MEAN A THING ON THE ROCKER

Re: Rocker Arms---Official Clarification

Quote:

Originally Posted by Rusty Davenport (Post 450705)

I witnessed this EXACT thing during a tear down after a record run.

Re: Rocker Arms---Does an official clarification exist

Since that is the official word, that's it. I wish a list of accepted rocker arms was available. That's how they determine the legality of a suspect rocker arm is by measuring lobe lift times the advertised ratio,then comparing actual lift at the valve.

Re: Rocker Arms---Official Clarification

I would really like to see that email. I believe there are a few tech men that would disagree with that. Jeff Teuton, if my memory is correct, was tossed for having rocker arms marked different than his spec even though the gross cam lift checked correct.

Quote:

Originally Posted by Rusty Davenport (Post 450705)

Re: Rocker Arms---Official Clarification

Quote:

Originally Posted by nolongerracing (Post 450721)

This was discussed on a previous post and Travis Miller made it clear the ratio can be checked.

http://classracer.com/classforum/showthread.php?t=25533