Rocker Arms---Does an official clarification exist

Rusty Davenport · 10-23-2014, 02:09 PM

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 ???

Greg Reimer 7376 · 10-23-2014, 02:52 PM

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.

Dwight Southerland · 10-23-2014, 03:21 PM

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

Myron Piatek · 10-23-2014, 03:23 PM

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.

Rusty Davenport · 10-23-2014, 04:19 PM

Quote:

Originally Posted by Greg Reimer 7376

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 ???

Rusty Davenport · 10-23-2014, 04:52 PM

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

terry1 · 10-23-2014, 05:28 PM

Quote:

Originally Posted by Rusty Davenport

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

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

Greg Reimer 7376 · 10-23-2014, 05:41 PM

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.

nolongerracing · 10-23-2014, 07:07 PM

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

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

SSDiv6 · 10-23-2014, 07:10 PM

Quote:

Originally Posted by nolongerracing

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.

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

10-23-2014, 02:09 PM	#1
Rusty Davenport Senior Member Join Date: Jun 2005 Location: Nashville N.C. Posts: 505 Likes: 4 Liked 100 Times in 26 Posts	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 ??? __________________ NHRA AND IHRA STOCK ELIMINATOR 2772

10-23-2014, 02:52 PM	#2
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,111 Likes: 164 Liked 649 Times in 208 Posts	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. Last edited by Greg Reimer 7376; 10-23-2014 at 02:55 PM.

10-23-2014, 03:21 PM	#3
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 1,980 Likes: 52 Liked 724 Times in 177 Posts	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?

10-23-2014, 03:23 PM	#4
Myron Piatek VIP Member Join Date: Nov 2001 Location: Florida Posts: 1,538 Likes: 34 Liked 132 Times in 48 Posts	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. __________________ LOCOMOTION Racing

10-23-2014, 04:52 PM	#6
Rusty Davenport Senior Member Join Date: Jun 2005 Location: Nashville N.C. Posts: 505 Likes: 4 Liked 100 Times in 26 Posts	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 __________________ NHRA AND IHRA STOCK ELIMINATOR 2772

10-23-2014, 05:41 PM	#8
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,111 Likes: 164 Liked 649 Times in 208 Posts	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.