Greg Gore

Possibly 1996 LT1/ LT4 only, apparently not used on 92 through 95 LT1. Anybody know where these could be obtained? OEM part number is 15713154 and is not available for ordering through dealer parts anymore.

Thanks, Greg

STL94LT1

Hmmm, I've never heard of a donut gasket on an LTx exhaust manifold.

I work for GM and we still use a a donut gasket on the LU3 4.3 engines. I'll bring one home and see if it will work on my LT1 manifols that I have laying in the garage.

Greg Gore

Manifold part number is different for 96 and incorporates the composite material donut seal. Looks like the catalytic converter flange on 95 and earlier does not require the "donut" and fits a radiused boss on manifold which 96 does not have. Any assistance on this one greatly appreciated!

LT1vette

Easy fix! Head to your muffler shop, Speedy, Midas, tell them what you need and they can order it if they don't have it in stock.

HTH LT1Vette

Greg Gore

Thanks for the help, mystery solved though. Part is superceded by #15170285 which is still available.

LT1vette

Greg...It'll be a lot cheaper at the muffler shop and the same quality if it's made by Walker. (they supply most of GM's exhaust), and it probably won't be a special order if it's a busy shop..............

TorchTarga94

Greg, I know I am bumping an 8 year old thread, but do you have any tips for getting the exhaust manifolds back on?

My passenger side manifold on my 94' was cracked so I purchased a NOS exhaust manifold from Rim Rock Chevrolet which requires the doughnut seal between the manifold and the down pipe like the 96's have. I purchased the GM Dough Nut gasket #15170285 and I cannot for the life of me get the manifold to line up properly with the head to get the manifold bolts started. I even went to advance to purchase the Fel-Pro variant part #61258 and it is identical to the GM seal.

Right now I have the manifold and seal in the freezer to leave over night and I'll try again tomorrow. It is almost as if the seal is too thick and the manifold is sitting up about a 1/16" too high.

Any tips or advice would be awesome.


Patrick

WVZR-1

Manifold needs installed to cylinder head "BEFORE" you install anything else. You can't connect convertor to exhaust and then install the manifold to engine.

I don't really catch your problem and don't see how the donut is related.

If you have a problem with the bolts to cylinder head "end to end" then you use a spreader but that's generally only required when replacing older/used manifolds. Maybe required new? I wouldn't think so.

TorchTarga94

Hard to explain without a picture I guess.

92'-95' Cars had a boss cast into the manifold that didn't require a doughnut. The newer replacement manifolds and the manifolds that come on 1996 cars require a doughnut between the down pipe and the manifold itself. You first have to push the seal into the collector of the manifold before you install it on the engine. The seal is so thick that when I set the manifold in place it interferes with the down pipe and I can't even get the bolts started into the cylinder head because the manifold is about 1/16" higher than it should be. Hope that makes sense.

With the old original 94' manifolds I am able to install them no problem with the cats still in place. Guess I will need to remove the cat first which I never had to do before. Then I will more than likely have trouble getting the cat lined up with the mounting bracket.

mtwoolford

Do the cats mount directly to the exhaust manifold and the rest of the exhaust mount up to the cat?

If so, it sounds like a mismatch of parts; I would really try to get a manifold with the stock boss cast into it; either that, or have a muffler shop weld a new flange on the front of the catalytic converter that will accommodate the donut ...and don't sic the fed's on me for suggesting a "modification" to a functioning catalytic converter.

WVZR-1

I understand exactly how the fit is accomplished and the "donut" acts just like the "ball-socket" on the old manifold. With the manifold on the engine, the seal/donut installed then the convertor goes in place and the three bolts allow the convertor to pull securely to the "donut" - just like the old arrangement. If you try it any other way for sure it should fail.

There's nothing unique with the donut/seal to the down pipe or convertor whichever. It's been used since maybe '95 on all GM's.

If the donut/seal is correct the sleeve needs to be inserted until the "flat of the donut" contacts the manifold. It's meant to be a force fit.

***See if your local AP store might have a FelPro 61012 - it seems that we used that when the pricing got ridiculous on the GM seal. That's a BEST I RECALL thing -

TorchTarga94

Okay, so ill remove the cat, install manifold with the donut, and then bolt up the cat with the 3 bolts. I appreciate it.

antfarmer2

Don't talk like that on a open forum good way to loose your job

antfarmer2

Ok just saw he was a old post but still not a good idea

WVZR-1

Is this DONE yet? It wasn't as aggravating as you expected was it?

TorchTarga94

Yes it is, and no it wasn't. I actually didn't have to remove the cat entirely, I just loosened up all the mounting bolts and it dropped a 1/2" or so. Bolted the manifold to the cylinder head and then tightened the cat back up to it. Not sure why I didn't think of doing that before. I was always able to install the old style manifold without unbolting the cat from its mounting bracket. Started right up, no leaks, sounds much better.

I appreciate the tip WVZR-1 . The exhaust system is finally where I want it to be (Except for Corsas ).