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 ???
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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.
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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?
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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
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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 |
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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.
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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.
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http://classracer.com/classforum/showthread.php?t=25533 |
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That's fine. Get it in writing, with the NHRA logo, and some sort of digital signature, and keep it with the car. There needs to be zero doubt that it is the absolute official word from NHRA @ Glendora. |
Re: Rocker Arms---Does an official clarification exist
I got thrown out 3 or 4 years ago for that. Cam checked, but rocker are stamped 1.65 and specs call for 1.60. I'm not sure if the rule has changed.
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Re: Rocker Arms---Does an official clarification exist
When did they go back to using a stock solid lifter to check lift? The last time I set the record they used there adjustable lifter. I think nhra. should sell a adjustable lifter if they are going to check with one. chevy stock solid lifter has different height than a smith lifter. I was told by well known engine builder that with roller rocker arms, longer & shorter push rods don`t change lift, like stock rocker arms. Tom
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Re: Rocker Arms---Does an official clarification exist
I've been involved in rules as well as in Tech at EMC. We were dealing with the same issue (rocker ratio) at Engine Masters Challenge. I have come to the conclusion the NHRA rule (As written) is not enforceable..I have had the input from a very notable former NHRA Tech person who is on our team and he concurs. That is the reason we have no Rocker Ratio rules at EMC. I think NHRA should re write that rule. I also think it is just asking for trouble to have any stamped ratios on rocker arms. When the wrong person tries to verify the ratio it can come up way wrong. That ratio number being wrong "could" be grounds for action by the NHRA.
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You are going to be allowed to match the overall height of what you're using. Trust me on that. |
Re: Rocker Arms---Does an official clarification exist
Yes, Mark after the fiasco in Div 4 concerning cam/valve lift I would think proper procedure might be followed a little closer.
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Re: Rocker Arms---Does an official clarification exist
Direct excerpt from 2014 NHRA rule book:
"ROCKER ARMS OEM or aftermarket rocker arm permitted.Needle/roller bearing pivots and roller tips are permitted for all applications.Must remain same design as original application(i.e. stud mount must retain stud mount, pedestal type must retain pedestal type, and shaft type must retain shaft type. Stud girdles prohibited.) Stamped steel OEM and OEM-type rocker arms may be reinforced." It's obvious what's not mentioned! |
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My 2 cents would be....who cares what any of the numbers are on any of the parts as long as the lift at the valve is within spec. The system can be engineered and designed to function much better and be a lot easier on parts than some of the stuff that's currently in use now, and still remain inside the "lift" rule |
Re: Rocker Arms---Does an official clarification exist
[QUOTE=Bill Diehl;450834]The ratio is listed in the blueprint specs
Your right. |
Re: Rocker Arms---Does an official clarification exist
I think the response to the question is being misinterpreted....there is a spec for total valve lift and a rocker ratio listed in the spec.....what Bruce said was " the cam lobe lift checked with a solid lifter and the numbers are good you are all set to go ".....in this case your rocker ratio better be correct or you will be bounced, I personally wouldn't mess with taking a chance on that...too expensive of a mistake......
D L Rambo......Stk 1300 |
Re: Rocker Arms---Does an official clarification exist
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" AS LONG AS THE CAM LIFT, CHECKED WITH A SOLID LIFTER, DOES NOT EXCEED THE SPEC YOU ARE ALL SET " |
Re: Rocker Arms---Does an official clarification exist
I wish I could use a .502 lobe on my combo:D
but the book says "cam lift" and we all know what that means |
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