Next are machined aluminum roller rocker arms, where the choices get really tricky. What appears to be a machined rocker arm may not be. Danny has found a number of rocker arms made from cast aluminum, which is why they're offered at such a low price. With modern technology you can make a cast rocker arm look just like one machined from high quality aluminum. Ask questions before you give your credit card number to the order taker on the phone.
When buying machined rocker arms you want four things: a rocker arm that's truly machined from a billet of aluminum; a rocker arm that's a true roller, with high quality roller bearings; a roller tip on the piece; and a part that actually fits properly.
Installation is easy, if you take your time. One very important step is to place the new rocker arms into position to make sure they don't hit the head casting. This is a really serious problem with some aftermarket rockers.
The really good rocker arms use a stud and nut to hold them in place. They also use pushrod guides to keep the pushrods in place.
The real trick is to tighten the nut on the rocker arm stud down far enough-but not too far. The LS engines all use zero valve lash. In the old days we used to tighten our small-block rocker arms down until we could no longer rotate the pushrod. On LS engines you can't even reach the pushrods. D.J. Racing has developed a little time saver here: a 0.001 feeler gauge. After rotating the motor until the appropriate valve is closed, tighten the rocker nut down until the feeler gauge is tight. The difference between 0.001 inch and zero is negligible.
Take your time and make sure everything is just right. If you get this wrong you could push a valve into the top of a piston-at 6,000 rpm. You don't have a lot of clearance to work with. Be careful.
Changing rocker arms won't give you that magic 50 hp that you see in the ads. It should give you at least 20 though, after about a day's work. Even if it takes you the whole weekend, that's no big deal. A weekend in your garage is far better than a day at work.