What do you do make them longer or shorter? Is it just a guess and run and if it hookes better your on the right track or is it known that you need to make them longer or shorter to hook?? I have an 89 Iroc with a 350 pushing out over 400HP and need some suspension work?????

Roughly...
1. You want the rear end to track the front

The left and right rear wheels shold be the same distance
from the left and right fronts.

2. You want the rear axle centered between the front wheels
(adjust panhard rod for this)

3. Now it depends on wheter or not you have LCA brackets..
For drag racing...

At the strip...
Have someone closely examine your launch and pay close attention to the angle of the LCA in the first 30ft .

Put the lca in the hole that will not allow the lca to swing beyond horizontal. That is the frame mounting point should always be higher than the mounting point on the transaxle.

For everything else ...
You need to talk to frikin or some such...

Making the adjustable LCA's either longer or shorter is done simply by rotating the LCA.

The goal is to keep the rear end centered vertically (eliminate wheel hop) during a launch. The only way you make the rear off center is by either adjusting the springs or by using different wheels.

The LCA relocation brackets give you more angles to play with.

There are lots of other areas to look at on a 400hp engine that constantly spins the tires.

Like Urban said, these adjustable LCA's are mainly to provide extra alignment for the rear of the car. Mainly if the car has been in an accident and the frame geometry is slightly tweaked, then theses are really needed.

Most racecars get slightly tweaked now and then.

As for shortening the lenght for better launches, I personally don't think this would help weight transfer unless they could be adjusted at least about 6" shorter to notice a difference. I think you have max. 1" adjustment for side to side. I personally like the adjustable rod ends buried as deep into the rod as possible thus exposing very few threads. I feel this is more safe from breaking.

p.s. I'm not big on drag racing, my passion is vintage roadracing.