Uh, the secret oil is secret because I forgot what the mix was. Man, i miss my brain...

One other thing on the operation of SU's. The common knowledge was running lighter oil in the damper allowed the piston to go up faster and hence you were at a lower point on the needle and therefore had more jet area exposed which equalled richer, which everybody associated with more power. The factory will tell you that slowing the damper down with thicker oil created a bigger vacuum, which resulted in more gas being pulled past the needle and hence a richer mixture. That was the case I always found on street cars, they ran better with thicker, or proper, damper oil.

Now that counters what I just told you in the previous post. We slowed the piston down to make it leaner. However, we're talking about two different regions of piston travel, rpm, and vacuum. The region of piston travel we care about on the track is the upper 1/3 of travel. On the street, the first 2/3. For rpm, above 4000 for track, below 4000 for street. For street rpm the throttle and piston position can affect vacuum greatly, for race the throttle is always full open when it isn't full closed (you Z pilots got that, right? Full open, there is no part throttle or "feathering" in a Z. If you can't do that we need to talk about shocks and setup), so vacuum is more a function of rpm, and less affected by the last 1/3 of piston travel than it is with the first 2/3. What we were slowing down was the last 1/3 of piston travel (and running stock like oil to have stock like piston response in the street range of throttle position and rpm). On a stock setup, when you open the throttle at 4000 rpm the piston pretty much goes straight to the top. The needle is essentially out of the jet so what is affecting your mixture is the vacuum over the jet bridge caused by increasing rpm. It ain't the piston moving the needle in the jet as you go from 4000 to 7000 rpm. So we slowed up the last 1/3 of travel, ran long needles with very little taper at the end, and lived with lean mixtures above 7k.

There used to be a video showing the piston movement during a dyno pull on ZTherapy's website. That was mine, very early in our engine program.