Modifying the '91-'95 Upper Intake Manifold

[sspeedstreet]

After talking to my local engine builder about the value of ExtrudeHoning my UIM (too little gain for too much money), he said a lot of guys cut the top off their manifolds and clean up what they can reach. So I cut the manifold open at the "turn" to see if there were any cleanup possibilities in the runners. I took a couple of pictures of my project in process:


Nothing really gross, a few dingleberries here and there. The inner radius of the "turn" is a parting line in the casting process, so it can use some cleanup:


The plenum area is an almost perfect 4" diameter cylinder:


So I've found a source for 4" diameter, 0.225 wall structural pipe that can be bought in as little as 24" lengths. That would give me a beautiful, smooth outer radius. Of course, I'd have to pull the UIM in order to get to the plugs. I have to figure a reroute for the TB coolant so I can do this without opening the cooling system.

Any thoughts on this? Will it be worth the trouble? And no, I don't want to change to the '96-'97 manifolds.

Neil

[Kohburn]

what did you use to cut it?

I'll be cutting one open later this year to gut it and install a hidden slim water/air intercooler setup.

[SappySE107]

As long as you don't use the transition part for the plenum to TB like the stocker, I think its a good idea. Hell, its basically what im in the middle of doing myself so that should tell you something.

[sspeedstreet]

As long as you don't use the transition part for the plenum to TB like the stocker

I'm not clear what you're referring to here.

Kohburn: I made the cuts through the radius with a band saw, then used a 4" cutoff wheel to start the long lateral cuts. I completed them with a hand held jig saw. It cuts VERY easily as it's only 3/16" thick and the material is hard and brittle. Brittle as in I think if you smacked the manifold on concrete it would break. There were stresses in it that bound up the sawblade while cutting and the final 1/4" snapped off while repositioning. Whole thing took maybe 20 minutes.

Any thoughts on rerouting the "O" ringed coolant passage?

[SappySE107]

Tap it and use a threaded fitting. Thats what I plan on doing. The transition im talking about is below the runners in your pictures. The thin area that leads to the TB. If you remove that and run the TB off the side of the tube, you won't have the restriction.

[sspeedstreet]

I looked at away to do that but I need to keep the EGR and it's smack in the way.

"Threaded fitting" isn't that going to lock the upper and lower together?

[SappySE107]

Well, if you are using your stock TB, i think its a waste of time. To keep the EGR and make a worthwhile intake, its going to be hard. The threaded fitting wouldn't get in the way if you don't have the stock TB sitting right there. In fact, if you do, i dunno what you have to worry about.

[RednBlack]

I think its a good idea. Hell, its basically what im in the middle of doing myself so that should tell you something.

It does sound like a good idea! I might even try it. :P Maybe even put a Monster TB on it.

[Lyle's GTP]

Has anybody ever thought of making something from plastic. I had talked to a plastics fabricator here in Edmonton once. I had some ideas for a custom air box. He said If I could build a mould out of MDF he could shrink ABS plastic over it. He also said that doing some plastic weldiing was another option aswell. He was really cool because he said he could made provisions for fastners and the whole nine.

So, since so many cars are going with plastic intakes any way why not do that. Shit, you could easily build a two stage manifold out of MDF and wood dowel and fiberglass. Make it two pleices then have it plastic-welded together. Not to mention, that the surfaces would be perectly smooth, no porting nessesary. He was telling me for the airbox design I had in mind it would be no more than 200 bucks.

I'm sure Ben that you know exactly the volume and and length of runners you want. I say start playing.

If, I wasn't planning to do a blower that's what I would do.

Lyle

[SappySE107]

actually, im still in the process of testing the lengths out and then ill tune the powerband more with the diameters. After that, I could very well do it with plastic. Not sure though with the TB tube yet though either so id have to see how much weight that has to support. Metal is going to be my first material.

[Lyle's GTP]

Well, you will have to put in the proper brackets to hold your TB and intake piping. I called another shop here and ran the idea by him and he said it shouldn't be an issue. He basically said come in show us what you have in mind and your heat requirements. Then we can decide on the material type and the process to mold the peice. He said they can design the mold, but it would be expensive. It would be best if it were done before hand. He said he would show me all the ways to make the mold to make it come together properly.

Lyle

[OldSkoolGP]

It's an interesting idea to be sure, but I have to wonder if it's trying to squeeze blood from a turnip. Maybe I'm reading into this wrong, but it sounds like what you're trying to accomplish is exactly what the 96-97 intake does, and it's a lot easier to bypass the TB coolant on a 96 intake. Say you come up with a way to make a 91-95 flow a lot better. Would you want to start making them for people?

BTW, this is reffering to the first post on here, I didn't read into what Ben and Lyle were thinking till after I typed this

[Lyle's GTP]

I believe what we are thinking is a dual stage intake. We know if you open up the intake you get stupid power all the way up to 8000 RPM. However the bottom end has like no power at all. But if you could besign an intake with short runners for the low end and a set of long ones for the top. You could then have a butterfly valve that changes between the two at a specific RPM. Therefore optimising your power output.

The problem is building a properly engineered intake isn't that easy. Building an aluminum shoebox for an intake is pretty easy, like that fiero guy did. But you loose all street driveability.

Lyle

[fieromadman]

i hope you meant short for higher rpms and long for lower rpms, otherwise I've been reading wrong for a LONG time!!

[Lyle's GTP]

Yeah, that's right. I'm wrong. School has me all twisted up. I got to get back to work turning wrenches, or I'm gonna go postal on some of my instructors.

Lyle