Ok, here's the deal...I got a 1986 wiring harness in my IROC. I'm buying a whole new system. I bought some good used SLP runners for the '89+ systems w/o the cold start injector. No problem there. I'm about to buy a 58mm TB and a Edelbrock TPI base...should I buy the early TB or late TB? My plenum is a ported '86 unit. Which should I buy, or does it matter? As far as the base goes, I'm assuming I should buy the early unit, since I plan on keeping EGR and will probably use TFS 23* aluminum heads. The main concern is which TB I should use since I no longer have coldstart, early or late with an '86 plenum?

 

You'll need the early style TB for the '86 plenum.

 

Also, the TB has nothing to do with the CS injector, that's in the runners only.

Differences in the TB's are where the IAC passages are, maybe something else, don't recall and it's too late to go out in the shop and compare spare parts

The base should match the head, some manufactures will work for both early and later style heads though.

 

The later tb's IAC air is entered into the two main bores, where the earlier ones went through the triangular hole between them.

 

cool...so I'll get the earlier TB!