Hello all, hopefully somebody can explain this to me better.

I'm installing an MSD Start/Retard box on my '96 Z-28 to use with nitrous. I've already got the MSD 6AL and appropriate MSD harness. I bought this box off a friend who bought it off E-bay with no instructions. It didn't work on his car so I sent it to MSD and they sent me a brand new box. I went online to MSD instruction download, but the only Retard box they have on there is the 3 step retard. I called MSD tech and got directions on how to install it (what wires go where.)

Also the instructions for the 3 step retard box state that just by hooking it up, it will retard your timing by 4* right out of the box and that you need to adjust for that. So I asked him if the same is true for the normal Start/Retard box. He said he was pretty sure, but not positive.

Does anyone know if this box will retard my timing 4* right away even when not activated by the nitrous kit?

Second, how can I check to see if it is affecting my timing? I figure I would notice a HP loss on a dyno with 4* retarded timing, right? So I could dyno and check the hp difference with the box hooked up and disconected?

My main dilemma is that the pcm will be calling for XX amount of timing, but the Retard box changes that at the coil/opti so the pcm will never know the difference, right?

I hope I was able to be clear about all that, and thanks for any and all help you can provide.