You can say that the root cause of the manifold cracking problems is that the manifold seeks to expand with heat, but it is restrained from expanding from the rigid cylinder head.
The conflict between both parts is resolved with cracking...
The intent of the bellows is to allow each part of the manifold to expand freely with the heat, stress-free (well, not completely free of stress, but far reduced).
Only a few thousand kilometres so far, so I cannot say that bellows are the final solution to 2.8 manifold problems, but so far things are looking good.
[This message has been edited by pmbrunelle (edited 08-02-2020).]
The odd thing is that the fro t and rear manifolds are almost identical and only the front one breaks. My theory has always been that the front one supports most of the weight and when support springs are missing too much weight is put on the front manifold.
I've only worked on Fieros in the "recent era", so after they've had recall work performed.
One difference between the front and rear manifolds is that one of them has elongated holes, while the other has smaller round holes. I don't remember which one was which.
There's also the dripping water factor; the instant cooling when a wet decklid is opened, pouring water on the front manifold.
[This message has been edited by pmbrunelle (edited 08-02-2020).]
There's also the dripping water factor; the instant cooling when a wet decklid is opened, pouring water on the front manifold.
That's always been my suspicion as to why the front exhaust manifold is more prone to cracking than the rear one.
Even the original weatherstrip (removed as part of a recall) along the leading edge of the decklid was kind of useless, as water would still get dumped down on the front manifold if the decklid was opened when wet.
The best solution was/is this - read from Here (make sure to click the link in the first post) and continue on down to the bottom.
[This message has been edited by Patrick (edited 08-02-2020).]
Aside from not fitting the rest of the system, the cast iron manifolds are heavier.
They did a fix on the 1988 Fieros - they ovalled the holes to allow room for expansion when they got hot.
This pic is a pair of manifolds I was using - the lower one shows the oval hole and the upper one has been machined out to give the up to 8 bhp boost that GM was too lazy/cheap to give you when they left the port half occluded by not milling the excess metal out. Takes about 5 seconds a hole with a set up machine or you can do it at home with a high speed grinder.
The odd thing is that the fro t and rear manifolds are almost identical and only the front one breaks. My theory has always been that the front one supports most of the weight and when support springs are missing too much weight is put on the front manifold.
fierofool, Where are the support springs supposed to be? Are you referring the the springs on the bolts that connect sections of the exhaust?
Correct. There is a pair of springs just below the downpipe flange. There are more over past the catalytic converter and about 3 on each end of the muffler. On the pipes, you will see a number of tabs welded to the pipe. In the same general area, there more tabs attached to the frame or cradle. They are all best seen from underneath the vehicle.
