I will be doing the dreaded exhaust manifold replacement on my 88 GT (with 3.4L conversion) soon. I've purchased the Fel-Pro gaskets and the Permatex copper spray. I am confused as to whether or not there is some sort of seal between the output end of the manifolds and the connection to the Y-pipe.

There is no item listed, and no picture of a seal, in the Parts and Illustration Catalog.

The service manual pictures no seal there at all but clearly shows a seal at the opposite end of the Y-pipe.

The General Description section of the Exhaust System chapter of the service manual states...

"The exhaust manifold to exhaust pipe connection is of the flex joint type, and requires a graphoil seal"

This Pennocks FAQs and How - To section post makes makes no mention of these seals at all.

https://www.fiero.nl/forum/Forum9/HTML/000016.html

The Autozone guy felt there should be some sort of seal (perhaps of the crush-able style?) there, but of course he is not a Fiero guy.

Hoping someone here can clarify for me.

Thanks

[This message has been edited by Rsvl-Rider (edited 05-31-2018).]

quote Originally posted by Rsvl-Rider: The Autozone guy felt there should be some sort of seal (perhaps of the crush-able style?) there, but of course he is not a Fiero guy.

No additional seal is used. The design of the mating surfaces (when tightened together) are what seals the exhaust manifolds to the Y-pipe.

[This message has been edited by Patrick (edited 05-31-2018).]

The joint between manifold and y-pipe is called a ball and socket. As designed, there is nothing else that goes there... no gasket, no RTV, nothing. If both sides are in good shape you really don't need anything either, but a thin film of RTV isn't a bad idea, just don't go bananas with it. You don't want it oozing out and breaking off into the cat.

Here's an example of what that joint looks like and how it fits:



You can clean both sides with some sandpaper to ensure a good fit. It's not a great joint (by modern standards) but functional and shouldn't be a problem.

On my car, the y-pipe was inexplicably crushed into an oval and it took a while to get it round again, but after some careful manipulation by various dies, it sealed up again fully.

[This message has been edited by thesameguy (edited 06-01-2018).]

Does anyone have idea on how to seal them up? I redid mine four times and still leak. No matter how tight i get those two bolts. I try cooper RTV and those turn into powder with an hr. Problem is you dont know if its fully seal until you put everything back and turn on the engine.

Be sure both sides are *perfectly round* and clear from any debris or damage. The mating surfaces need to be the same shape and completely smooth - any deformations or pitting or rust etc. will prevent a seal. If they're the absolute best they can be, you can try exhaust paste to help complete the seal. Walker Exhaust sells a product called "muffler cement" that works very well - be sure to follow the directions and be aware it could be messy next time you take it apart.

Both ends of the ball and socket joint must be carefully aligned for a tight seal. If you are trying to join them at an angle (one bolt screwed in/tighter than the other) the unequal joining of the pipes can cause a leak. The manifolds do get very hot so the seal is by a pressure fit. There are few sealers that won't burn out.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Can you name those sealers that won't burn out? I assuming those sealant needs to be flexible too? thanks

quote Originally posted by thesameguy:Walker Exhaust sells a product called "muffler cement" that works very well - be sure to follow the directions and be aware it could be messy next time you take it apart.

quote Originally posted by Ucycle: I assuming those sealant needs to be flexible too?

Why do you make that assumption? Once the Y-pipe is tightened to the exhaust manifolds, nothing's moving.