Because your burning a hotter more powerful cumbustion you want start the burn sooner to get a complete burn. Oh and what MSD system? Some automatically retard timing when they sence boost. I think its the 6AL. I dunno. Id also look into a fuel pump and AFPR if your planning on running 70-75 shot. Just to be safe.mteg said:So I'm safe with iridium plugs? I heard about retarding the iginition a few degrees, but why the timing? I was just going to install an MSD ignition.