[Alan Roehrich]

The only problem with the idea of altering lobe lift is this: If you alter your valvetrain geometry so that you reduce the lobe lift necessary to achieve near maximum lift, you may change your rocker arm ratio so that it is outside the legal limit for your particular engine.

This can go either way. You could end up needing more lobe lift, meaning your rocker arm ratio has been effectively reduced at maximum lift. However, you could also end up needing less lobe lift, because you have eliminated lost motion, and effectively increased your rocker arm ratio. As far as I've read, and from the answers I've been given, if you end up with less than maximum rocker arm ratio, and needing more lobe lift, you are technically legal. If, on the other hand, you end up needing less lobe lift, because you end up above the maximum rocker arm ratio, you are illegal, even though you have legal rocker arms.

For example, let's say you are allowed 0.520" lift, using the rectangle port solid lifter big block Chevy cam engines. You're allowed a 1.7:1 rocker arm ratio, according to the blueprint spec, and your lobe lift will be approximately 0.306". Suppose you correct your geometry, and eliminate the scrubbing and thrust caused by lost motion, so that 0.306" lobe lift yields 0.540" at the valve. You have effectively increased your rocker arm ratio, even though you have not changed the rocker arm. So, your rocker ratio at max lift is now 1.76:1. You now need a 0.295" lobe lift, to get your valve lift down to 0.520". We'll ignore the fact that you really want it around 0.515" so that you're safe going through tech.

The problem is, if you go back and read NHRA Division 3 tech guru Travis Miller's posts, is that NHRA is not going to like your new effective rocker ratio, since it now exceeds 1.7:1, the maximum allowed.

Now, you might get through "basic tech" where they pop a valve cover or two off and check lift at the valve, but if they check lift at the valve and lift at the lobe, or even the end of the pushrod, and do the math, guys like Travis are known to do so, you may fail tech.

A rocker arm is not a constant ratio device, it is a constantly variable ratio device, the ratio changes as you move through the lift curve. You alter that ratio as you change pushrod length and or valve length, and the relationship between them, as well as where the rocker arm is on the stud when valve lash is adjusted.

Yes, as Bub stated in reply to Grant, getting the scrubbing and the thrust to a minimum, thereby reducing the force necessary to open the valves, is what you want. However, in Stock Eliminator, if you substantially alter the rocker ratio in the process, you can find yourself in an unhappy situation in the tech barn.

Remember, when you change camshafts, you may or may not get the same exact base circle, if you do not, you will have to start all over again. You will also find that your cam grinder may not have the lobe design you need with the lift you want. Now, if they use a CNC grinder, they may be able to easily go in and change the lobe lift. However, in doing so, they may alter the lobe design. If their Stock Eliminator cams are ground from masters, or they are unwilling to write a new CNC program, you may be stuck. This is where you need a really good relationship with your cam grinder. Adding or subtracting a few thousandths of an inch of lobe lift is not nearly as simple and easy as changing deck height or pushrod length.