Whats the difference between the 85-88 and 89-92, plenum and runners? And how do I know which to use? My 350 TPI is out of an 87, but i'm going to have the 88 and up serp belt setup. So is that going to make a difference? Also, I'm going with vortec heads and SDPC TPI baseplate. Figured i'd port my plenum and get bigger runners, but dunno which brand and what year will go well with ported plenum and the SDPC TPI baseplate.

 

Pre- '89 runners had provisions for the CSI (cold start injector). It was eliminated in '89 along with a prom change. I believe the plenum is the same for all years. You need to use pre '89 aftermarket runners if you are using the stock '88 tpi prom w/CSI. All aftermarket runners are pretty close in flow performance. I would say get the least expensive - it may be the SLPs.

 

Pre 89 plenums have provisions for cold start injector as well