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...