I know this has nothing to do with the LS1, but I put one one my old 1999 GMC Z71(new body) with the 5.3 in it. I personally didn't see any noticable gains in performance or economy. I think the are a waste of $100 for straight induction like the LS1 and the 5.3 truck engine. But like CMNTMXR57 said, I have heard that they work alot better with Carb engines, or where the TB in located ontop. As for LS1 TB spacer, if they even make one, nah.