[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?