[Greg Reimer 7376]

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.