Rocker Arms

[Jeff Lee]

Originally Posted by mtkawboy

Im not sure you understand what Jeff is telling you, the cam still has to check at legal lift specs so theres no advantage with the higher lift rockers. Maybe Im misunderstanding him too, who knows.

It does not matter what the lobe lift is, tech will check the lift as measured at the valve spring retainer with zero lash in the checking lifter. The checking lifter will have the same plunger height in relationship to the lifter body as the one the racer is running.

If you have a "true" 1.5 rocker ratio, the lobe lift will be .333" if you have a cam spec of .500".
If you still have the same cam spec of .500" and want to use a 1.6 rocker ratio, the lobe lift will be .3125".

It's up to the racer to determine what rocker ratio he wants. That choice may be limited with a stamped steel ball stud arrangement. Maybe rocker to valve spring clearance comes into play as well.
But a higher (numerically) ratio will open the valve at a faster rate. The bottom line is, it can't open the valve more than .500" in this scenario.
You can juggle with Chevrolet ratio and Pontiac ratio if that's what you want to do.
I found on the AMC which is advertised as 1.6 (also stamped steel ball / stud system) most rockers checked at 1.55 or so and a SBC 1.5 ratio rocker was around 1.45. Since I was always using custom cams, I had the lobe lift adjusted to compensate for the true rocker ratio. Keep in mind what was said earlier, your net valve lift can be adjusted by pushrod length (or even plunger height).
The engines with shaft rockers like a mopar have it easy. The ratio is fixed. And with offset grinding of the shaft hole in the rocker, the ratio can be adjusted. I believe those racers are in the 1.85 range and I think they have been around the 2.0 range but I don't know as a solid fact. But it is allowable.
I know this, when I switched from Stock to Superstock and having a shaft style rocker system from T&D sure made it a lot easier. Where I once adjusted valves every 2-5 runs, the T&D is set and forget (as long as there are no problems of course). And we tried different ratio's on the dyno. There is a difference that can be seen in RR both intake and exhaust.
Hope all this helps...

[Travis Miller]

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.)

[Shawn Blair]

Originally Posted by Jeff Lee

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

Looks like they need to start checking rocker ratio at teardown, just in case they thought it was "OK".

Shawn 6383

[Jeff Lee]

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]

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]

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]

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]

[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]

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]

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.