Hi guys,

I just got done doing a 355 TPI swap on the IROC. We used a 91 corvette block/heads. The block had to be decked .015 I think it was from the machine shop when I got it hottanked and bored .030.

Anyways she is in the car and running now here's the problem. I am running MAF with the car. Apparently come to my attention I have a later SD plenum with early MAF runners (w/ CS injector). I am guessing since I used this setup off of my old 305 that the TB is for a later SD system as well to correctly mate with the plenum?

Why I ask is I was noticing that the drivers side small runner tube in the middle has nowhere to 'connect' to on the plenum. So We tried plugging it up with some gasket sealer and a piece of rubber. Dont know how well it worked or not. But that may not be the only vaccum leak.

Would the TPIS lower manifold be a problem with the block decked .015 as well? I would like to tackle this myself before I go taking it somewhere to get it running right. She will fire right up and then want to die unless you give it gas. I mean we may have to adjust timing and such still but you can hear the hissing with the vaccum leak.

My Plenum/TB/Runners are all nice and polished but if they are going to cause problems I guess I'll have to get the right parts either way. Any suggestions?

 

The throttle body, plenum, and runners are a matched set. Mixing these causes problems with IAC behavior, as the passage location changed for '89 and up.

Putting an older TB and plenum onto newer runners gives the IAC air no way to enter the intake if I recall right...that's what that extra tube you blocked off does.

Not sure how you might hack these up to work together correctly, or if it's even possible.

Short term you can work around the IAC problem you're having by just adjusting the min air screw on the throttle body to give it enough air to idle.

 

So basically to make it run right if it is the runner situation is to get the correct 85-88 plenum w/ CS runners and correct TB. How do I tell which TB I have currently? Is there a way to tell a difference...