Rocker Arms

[Dwight Southerland]

Originally Posted by Geerhead55

Not sure what the ruling is on rocker arm ratio,,,but some of the old timers might remember the story about Bill Jenkins using Ford 289 rocker arms on his A/S 66' Chevy II(327 4speed) back in the day against Jere Stahl's A/S 66 Hemi Plymouth. He was thinking outside the box, as usual. Danny Durham

That may be a myth. The rules that year allowed those cars to use any aftermarket flat tappet camshaft and valve train. When I saw his car race at Tulsa that year, he had roller rocker arms.

[Jack McCarthy]

elgin rocker arms, then ship to jim bailey he will harden and polish them... shazaam nice pieces and very reasonable pricing

captain jack

[Eddies66]

Any ruling on the ratio? I have an article written in Oct 1966 "What Makes Bill Jenkins' Chevy Run" He ran a Isky 550 flat tappet cam with a 108 centerline and Crane roller-tip rockers. Not real stock for a stock class but I guess those were the rules.

[Jeff Lee]

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

[Eddies66]

Jeff, thank you for the information. I was reading an article about a gent with a 409 that found a Canadian source for stamped steel rockers that were 1.7. It was a simple question and all I need was a straight answer. I guess it's an Arizona thing about looking a man in the eye and getting a straight answer.

[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.

[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.)

[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...