Gasket matching Upper intake runners

[jmgtp]

As for the original post.

I use a marker as well, seems to do ok for me. You will want to match the lower to the plenum, and go at least 1" in on both to blend it in. You can open them up more if you like, the lower has plenty of room for improvement. You aren't looking at much for gains past a gasket match but if you have the time you can do a better job than that.

Hmmm... I really don't remember mine being like that. It's been a while since I have had a gasket up against the 91 manifold, but I'm pretty sure my 96 manifolds were no where near as bad as that. When I got them I took the time to match the TB arm to the TB, cause the TB is offset and it matches up terribly. I used a gasket to compare the upper to lower intakes, and they were so close to the gasket that it didn't warrant any work. I have a spare 96 manifold and I'm sure an old gasket lying around, I'm going to see if the 96 had a better cast. Also, the 96 lower intake to heads gaskets don't seem to have the design flaw of pre 96 gaskets, and match up much better, without 1/8" of plastic all around interupting airflow.

Regardless... these manifolds are cast aluminum, correct? Meaning each one is going to vary, some would match better than others.

[SappySE107]

Yeah, but that is really only gonna vary for the casting flash. There will be some variance but for how bad every single 91-95 plenum has been that I have seen, you wont find a perfect one unless GM changed their casting somewhere along the way.

[jmgtp]

I just went down to the basement and dug up my old 91 lower intake manifold, which still had the gasket on it. It really isn't nearly as bad as the pic posted. It is not perfect though. The corners of some of the ports do not match the gaskets so well - as in the gasket is larger or more uniformly shaped in the corners of some ports. But the 'walls' of the ports all seem to match up well. Maybe I'm just seeing what I want to see :P

I have a 96 lower intake sitting on my workbench, but couldn't find a spare plenum gasket to do any comparisons. I think my 96 hardware matched up pretty well, but I guess I can't say for sure. But, honestly the lower intake gaskets on the 96 seem much better than the earlier generation.

[SappySE107]

They probably do match up better for 96. I also have a set of 96 lower intake gaskets...the blue rubber ones. I dunno how well they work but the rubber is MUCH thinner. Gonna be interesting.

[jmgtp]

They probably do match up better for 96. I also have a set of 96 lower intake gaskets...the blue rubber ones. I dunno how well they work but the rubber is MUCH thinner. Gonna be interesting.

I was skeptical about how thin the rubber was too. I used some hi temp rtv around the coolant ports for good measure. No leaks, coolant or vacuum, so I guess they get the job done. What I like about them is that they dont have a lot of plastic hanging into the port to disrupt air flow.

[SappySE107]

I just compared them...and the 96 uses a larger port shape for the gaskets. The amount of plastic is the same but its basically just out of the way now. The 96 also completely seals off the unused opening in the head...wondered what that open space was for and now it appears it does nothing. I like these so much more right now, because they actually have plastic that goes to the bolt hole near the coolant passage. Hello revision The actual thickness of the plastic is thinner on the 96 as well. I hope they work for 91-95 but im having my doubts at the moment.

[grandprix34]

got the plenum off and about to start working on it...

one question though, what can i do about the TB? I know i can't overbore the actual butterfly opening but what can i do about the front part of the TB?

By the way, Ben, could i send you my plenum later on and have you install one of those new butterfly plates you got? How mucH?

[dykz34]

You can always taper the TB opening.

I, too, have heard that the 96 castings are much better. I've seen one in person and the gaskets were almost perfect.

[grandprix34]

well here are some pics of how it went:

[grandprix34]

Here are the final results. The work done on these is very minimal and I realize that. THe next step would be to take off the lower intake manifold as well and port that too. The gasket showed TREMENDOUS casting flaws for the lower intake as well.

[dykz34]

Looks good!

[grandprix34]

I also solved a problem putting the intake back on that i didn't realize. The plenum comes complete as TB and intake and at the corner of the TB, there is an opening for the EGR valve. I did not have the gaskets necesarry so what i did was use RTV high temp silicone sealer and a coke can =)

I cut a piece larger than the intake opening and sealed it shut using the RTV sealer. Likewise on the EGR valve itself, I just sealed that up too.

Bolted everything up and started her up....man the idle STAYED at like 900, 800 RPMS...usually the damn thing would dash to 1200RPM's then slowly climb down as the Idle Air Control valve compensated.


Also, here's the pic of the heads i just got in the mail: Gonna be fun!

[93vinx]

hmm, somone show me how to post pics and i'll show you mine i'm definatly a coupple inches depper and little better in the rounds.

[RednBlack]

If you need to get deep in your polishing, there are mandrels made to go about 4" in. I have bought them from Grainger and McMaster/Carr. Costs about 3 bucks each. Fits the paper rolls. Has 1/8" chuck size. Cannot run at high RPMs. Now if you want to diamond polish........Many more dollars! (have to buy the compound) Never done it on a head or intake yet, just on a plastic injection mold, but it looks good! Mirror finish! You can pop a zit in it! Not sure if the results would be worth the trouble. 93 send me your pics. I can post them for you. Have to have a sizing program.

[93vinx]

i heard the last turn in the manifold befor it goes to the lower was the most restrictive, is there any truth here? also my intake is ported all the way to the turn and rite now i'm testing ways to go further, why does everyone stop after 2 inches?, i have also blocked the egr port and have ported and smotthed about 6 inches into the plenum, i'm useing some nice ass bits though, rednblackcutlass wil host pics