Rocker Arms

Travis Miller · 05-06-2010, 02:11 PM

Quote:

Originally Posted by Jeff Lee

You can run any ratio as all that is checked is lift as measured at the valve.

Not so, Jeff. The rocker arm ratio for Stock Eliminator engines are still listed in the Engine Blueprint Specifications on NHRA.com.

While it is true that the Tech Dept checks valve lift at the retainer, we can still check rocker arm ratio if we so desire. That could happen anytime we run across a set of rocker arms that do not appear to be correct. A racer was DQ'd a few years ago at Gainesville for using 1.6 rockers on a SBC even though the lift at the valve met the spec.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

Jeff Lee · 05-06-2010, 04:58 PM

Quote:

Originally Posted by Travis Miller

Not so, Jeff. The rocker arm ratio for Stock Eliminator engines are still listed in the Engine Blueprint Specifications on NHRA.com.

While it is true that the Tech Dept checks valve lift at the retainer, we can still check rocker arm ratio if we so desire. That could happen anytime we run across a set of rocker arms that do not appear to be correct. A racer was DQ'd a few years ago at Gainesville for using 1.6 rockers on a SBC even though the lift at the valve met the spec.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

I suspect that would be a tough one to handle since you (I assume unless you correct me) do not have a tolerance. Since a 1.6 RR may check out to 1.53-1.55, is that within the tolerance allowable for an advertised 1.5 RR?
And if the tolerance is "dead nuts", you would be able to throw just about everybody out. Right?
My guess is somebody in Gainsville a few years ago must have really PO'd a tech guy off to get bounced for that...

Bub Whitaker · 05-06-2010, 05:13 PM

I agree with you Jeff, if they did the lobe lift to the valve lift to check R Arm ratio.. everybodys out... good luck with that NHRA Tech...

BRUCE PARSONS · 05-06-2010, 06:27 PM

Typical NHRA tech.....a few can interpet the rules completely different than a few hundered racers. I can't wait to see what they'll use to check with!

Travis Miller · 05-06-2010, 07:48 PM

Quote:

Originally Posted by BRUCE PARSONS

Typical NHRA tech.....a few can interpet the rules completely different than a few hundered racers. I can't wait to see what they'll use to check with!

Bruce, rocker arm ratio is very simple to check. One only needs to know two numbers. Cam lift read at the lifter and valve lift read at the retainer. Simple math gives the ratio.

Jeff, the racer that got DQ'd did not PO the techman. I was quite calm about the situation. When the cam came up way short, I asked him where the rest of his rocker arms were. Seems he had two on the engine and sixteen in the trunk. Two from the trunk made the cam read correct at the retainer but when I checked the cam at the lifter and did the math, it came up more than the listed 1.5 ratio. His engine builder told him over the phone that any rocker ratio was allowed as long as the cam checked at the retainer. His engine builder was wrong.

For the racers following this discussion, rocker arm ratio is a spec listed in the Engine Blueprint Specifications on NHRA.com. Up until now it was something we only checked if the rockers did not appear to be correct. Now it seems that some have shown their hand and we may have to look more closely.

It's amazing what an open forum will bring to light.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions. And I was only letting everyone know what the rules were. I did not realize what would be exposed.)

BRUCE PARSONS · 05-06-2010, 08:23 PM

[QUOTE=Travis Miller;186147]Bruce, rocker arm ratio is very simple to check. One only needs to know two numbers. Cam lift read at the lifter and valve lift read at the retainer. Simple math gives the ratio.

That will not give you the true rocker ratio. That will only give the ratio as ran. As you know cam base circle, lifter seat height, pushrod length, and valve stem height figures into the sum. I suppose you have all the "stock" dimensions for that too. You'll need to have an "off the car tool" to check the rockers the right way...not the NHRA way.

Alan Roehrich · 05-06-2010, 08:37 PM

Travis,
In the interest of trying to be legal, and trying to get along with the Tech officials, exactly what is the tolerance here.

Lets be brutally honest about this stuff.

First off, stamped steel ball and stud rocker ratios vary, in no small amount, when checking real factory stock pieces. A stock GM 7/16" stud 1.7:1 big block Chevy rocker may check anywhere between 1.65:1 and 1.74:1 or so, and that's out of maybe 30 pieces. That's JUST the rockers themselves, with NO other changes. You might not find a set of 16 that are exactly 1.7:1 out of 100 rockers. I know, I've sorted them that way. And that was genuine GM stuff, not aftermarket stuff.

Second, we all know that rocker arms are NOT a truly constant ratio device. Change ANY of the three points of the fulcrum, and the ratio changes. This means that as the rocker travels from valve closed to maximum valve lift and back, the actual ratio of the rocker changes. This also means that changing pushrod length changes rocker ratio.

Third, we also know that valvespring pressure changes the amount of lift generated. I can increase my seat and open pressure by 50 pounds or so and my lift may change 0.020".

Also, we had an engine at one point that actually had a cam with extra lobe lift ground in because they could not get to the factory valve lift.

So exactly what tolerance exists? If I put a short pushrod in so that I'm 0.010" under the valve lift spec and have enough piston to valve clearance, and that reduces my rocker ratio slightly, have I made the engine illegal? If an engine has a geometry problem, and I need an extra 0.005" lobe lift to get within 0.010" or so of the correct valve lift, is that illegal?

J Giermanski · 05-06-2010, 10:06 PM

Just a novice here asking a stupid question and trying to learn something. What differance does it make if the spec is correct at the retainer? The valve will not open any more or less. Am I wrong on this? Thanks for your help.

Travis Miller · 05-06-2010, 10:42 PM

To Bruce, Alan, and anyone else concerned with this rocker arm discussion,

I got in this discussion when the statement was incorrectly made that any rocker arm ratio could be used. That led people to believe that it was legal to use 1.6 or 1.7 rockers when the specs call for 1.5 rockers. Then it expanded to therotical measurement using off the car tools. We could not care less what the rocker arm ratio is when it is laying on the workbench. We are concerned with the "as run on the engine ratio". That ratio is figured by taking the lift at the retainer and the lift at the lifter then doing the math. As long as that ratio does not exceed the spec in the Engine Blueprint Specification for an OEM or accepted replacement rocker arm, it will pass.

We know that the ratio of stamped steel rocker arms can vary, usually to the short side. That is why the spec given is the max allowed. However an OEM rocker arm that the factory says is 1.5 is not going to figure out to be 1.6 or 1.7. That ratio comes from using the wrong rocker arm. If the spec says that the ratio is 1.5, then that is the max the ratio can be. If anyone wants to play with having a cam ground to make up for factory shortcomings, fine. Just be sure you meet the lift specs at the valve retainer and you do not exceed the rocker arm ratio specs. If you do happen to run across a rocker that exceeds the spec for the ratio, then its simple...do not use it.

Now you know how we check ratio....lift at the valve retainer and lift at the lifter, then do the math.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

Jeff Lee · 05-06-2010, 10:48 PM

Quote:

Originally Posted by Alan Roehrich

Travis,
In the interest of trying to be legal, and trying to get along with the Tech officials, exactly what is the tolerance here.

Lets be brutally honest about this stuff.

First off, stamped steel ball and stud rocker ratios vary, in no small amount, when checking real factory stock pieces. A stock GM 7/16" stud 1.7:1 big block Chevy rocker may check anywhere between 1.65:1 and 1.74:1 or so, and that's out of maybe 30 pieces. That's JUST the rockers themselves, with NO other changes. You might not find a set of 16 that are exactly 1.7:1 out of 100 rockers. I know, I've sorted them that way. And that was genuine GM stuff, not aftermarket stuff.

Second, we all know that rocker arms are NOT a truly constant ratio device. Change ANY of the three points of the fulcrum, and the ratio changes. This means that as the rocker travels from valve closed to maximum valve lift and back, the actual ratio of the rocker changes. This also means that changing pushrod length changes rocker ratio.

Third, we also know that valvespring pressure changes the amount of lift generated. I can increase my seat and open pressure by 50 pounds or so and my lift may change 0.020".

Also, we had an engine at one point that actually had a cam with extra lobe lift ground in because they could not get to the factory valve lift.

So exactly what tolerance exists? If I put a short pushrod in so that I'm 0.010" under the valve lift spec and have enough piston to valve clearance, and that reduces my rocker ratio slightly, have I made the engine illegal? If an engine has a geometry problem, and I need an extra 0.005" lobe lift to get within 0.010" or so of the correct valve lift, is that illegal?

All correct and good points.
I would ad that since NHRA allows for an adjustable pushrod (no spec given), or adjustable rocker (but not both), and doesn't check lobe lift (as the spec is not given), and clearly indicates that lift is measured at the retainer, that it doesn't really matter what the RR is.
I wont pretend that I've checked even a small percentage of the millions of stamped rockers out there, but the ones I have checked, buckets full, have NEVER checked exactly as advertised. I don't recall ever checking a 1.5 SBC or 1.6 SBC or 1.6 SBF or 1.6 SBF that ever showed a higher than advertised RR. But I'm sure some are out there.
So from there, I must conclude there has to be a tolerance. And I would bet the SBC racer in Gainesville had an advertised rocker that in reality was 1.5something. Do we round up or do we round down?
Tech can bust any racer out there at anytime for any reason. I just can't believe with no tolerance given in such a sloppy atmosphere of undefined specs (the valve train) that this is an area of concern.
Yes, It's amazing what an open forum will bring to light.

05-06-2010, 05:13 PM	#3
Bub Whitaker Member Join Date: Feb 2005 Location: Dayton, MD Posts: 222 Likes: 0 Liked 1 Time in 1 Post	Re: Rocker Arms I agree with you Jeff, if they did the lobe lift to the valve lift to check R Arm ratio.. everybodys out... good luck with that NHRA Tech... __________________ Bub Whitaker

05-06-2010, 06:27 PM	#4
BRUCE PARSONS Banned Join Date: Jun 2004 Posts: 32 Likes: 0 Liked 0 Times in 0 Posts	Re: Rocker Arms Typical NHRA tech.....a few can interpet the rules completely different than a few hundered racers. I can't wait to see what they'll use to check with!

05-06-2010, 08:23 PM	#6
BRUCE PARSONS Banned Join Date: Jun 2004 Posts: 32 Likes: 0 Liked 0 Times in 0 Posts	Re: Rocker Arms [QUOTE=Travis Miller;186147]Bruce, rocker arm ratio is very simple to check. One only needs to know two numbers. Cam lift read at the lifter and valve lift read at the retainer. Simple math gives the ratio. That will not give you the true rocker ratio. That will only give the ratio as ran. As you know cam base circle, lifter seat height, pushrod length, and valve stem height figures into the sum. I suppose you have all the "stock" dimensions for that too. You'll need to have an "off the car tool" to check the rockers the right way...not the NHRA way.

05-06-2010, 08:37 PM	#7
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,105 Likes: 1,564 Liked 1,789 Times in 408 Posts	Re: Rocker Arms Travis, In the interest of trying to be legal, and trying to get along with the Tech officials, exactly what is the tolerance here. Lets be brutally honest about this stuff. First off, stamped steel ball and stud rocker ratios vary, in no small amount, when checking real factory stock pieces. A stock GM 7/16" stud 1.7:1 big block Chevy rocker may check anywhere between 1.65:1 and 1.74:1 or so, and that's out of maybe 30 pieces. That's JUST the rockers themselves, with NO other changes. You might not find a set of 16 that are exactly 1.7:1 out of 100 rockers. I know, I've sorted them that way. And that was genuine GM stuff, not aftermarket stuff. Second, we all know that rocker arms are NOT a truly constant ratio device. Change ANY of the three points of the fulcrum, and the ratio changes. This means that as the rocker travels from valve closed to maximum valve lift and back, the actual ratio of the rocker changes. This also means that changing pushrod length changes rocker ratio. Third, we also know that valvespring pressure changes the amount of lift generated. I can increase my seat and open pressure by 50 pounds or so and my lift may change 0.020". Also, we had an engine at one point that actually had a cam with extra lobe lift ground in because they could not get to the factory valve lift. So exactly what tolerance exists? If I put a short pushrod in so that I'm 0.010" under the valve lift spec and have enough piston to valve clearance, and that reduces my rocker ratio slightly, have I made the engine illegal? If an engine has a geometry problem, and I need an extra 0.005" lobe lift to get within 0.010" or so of the correct valve lift, is that illegal? __________________ Alan Roehrich 212A G/S

05-06-2010, 10:06 PM	#8
J Giermanski Junior Member Join Date: Sep 2008 Posts: 43 Likes: 1 Liked 4 Times in 2 Posts	Re: Rocker Arms Just a novice here asking a stupid question and trying to learn something. What differance does it make if the spec is correct at the retainer? The valve will not open any more or less. Am I wrong on this? Thanks for your help.

05-06-2010, 10:42 PM	#9
Travis Miller Member Join Date: Jun 2007 Posts: 478 Likes: 1 Liked 276 Times in 27 Posts	Re: Rocker Arms To Bruce, Alan, and anyone else concerned with this rocker arm discussion, I got in this discussion when the statement was incorrectly made that any rocker arm ratio could be used. That led people to believe that it was legal to use 1.6 or 1.7 rockers when the specs call for 1.5 rockers. Then it expanded to therotical measurement using off the car tools. We could not care less what the rocker arm ratio is when it is laying on the workbench. We are concerned with the "as run on the engine ratio". That ratio is figured by taking the lift at the retainer and the lift at the lifter then doing the math. As long as that ratio does not exceed the spec in the Engine Blueprint Specification for an OEM or accepted replacement rocker arm, it will pass. We know that the ratio of stamped steel rocker arms can vary, usually to the short side. That is why the spec given is the max allowed. However an OEM rocker arm that the factory says is 1.5 is not going to figure out to be 1.6 or 1.7. That ratio comes from using the wrong rocker arm. If the spec says that the ratio is 1.5, then that is the max the ratio can be. If anyone wants to play with having a cam ground to make up for factory shortcomings, fine. Just be sure you meet the lift specs at the valve retainer and you do not exceed the rocker arm ratio specs. If you do happen to run across a rocker that exceeds the spec for the ratio, then its simple...do not use it. Now you know how we check ratio....lift at the valve retainer and lift at the lifter, then do the math. Travis (Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)