I'm working on replacing the exhaust system on 'BIGBRRD' (a '78 Trans Am w/Pontiac 400ci).  The pipes from the exhaust manifolds come together before the cat, then after the cat a pipe spilts to dual mufflers and pipes again.  Everything is SO DM rusty...!!!  I don't have a 'blue wrench' so have been using a sawz-all and hacksaw to get things apart.  So far I've cut the mufflers and rear pipes off and cut off the bolts heads at the rear of the cat.  The joints on either side of the cat are rusted so bad that they appear to be welded (so you can imagine what the bolts look like!). 

After spending 4 hours under the car last night I've come to the opinion that I'm going to have to unbolt the exhaust manifolds and drop the whole mess as a unit in order to make it easier to get things apart.  I'm certain that when trying to separate the manifolds from the front y-pipe I'm going to snap most of the manifold studs.

First question: what problems would I create by not replacing the cat (becuz the car is now 25 years old I don't think Minnesota cares about the cat anymore and we don't have annual inspections) thereby converting it to a true duals setup?  Any carb or ignition tuning issues I would need to worry about (it does have electronic ignition)?

Second question: should I spend the time to overhaul the original manifolds and reuse them or bite the bullet and get a set of headers?

The car is a cruiser ("Frog" (aka - my bride and owner of the car) will not allow racing of ANY sort with it) so additional performance is not a requirement.

Jim,
I did mine from the manifolds back, eliminated the cats and ran true duals out the rear. I didn't change the timing or carb. I couldn't be happier with the results. It sounds great!
Scott

There will be no problems not replacing the cat.  In fact, it may run better.

You may want to consider cutting the pipes behind the manifolds, and not even trying to remove the rusty bolts.  Then once the manifolds are removed you can take them to someone who does have the blue wrench to remove the bolts.  That way it's much easier than trying to remove broken bolts.  Food for thought.

Hey, Norsky........What's it like livin' up yonder in th' RUST BELT?!!!

I'd go with Ken's suggestion, and whack the pipes off just below the mfld, and then pull them(mflds) off. It's a lot easier to get a broken stud out that way.

oh, yeah........I'd go ahead and replace the whole mess, front to rear, while you're at it. Adams' Apple38617.7625462963

Thanks guys.     

I already have everything new from the cat back to install.  Getting things apart has been the problem.  Zipping the y-pipe will make getting the manifolds off a lot easier.  I just didn't know if I'd need to use it again. 

Several  of the Firebird parts places have a direct business link with an outfit named Pypes Performance Exhaust where I can get the parts between the manifolds and the mufflers that I need.

Tally ho...!!!

* * * Update! * * *
Ordered down pipes (to use with the stock manifolds) and an X-pipe to replace the rest of the system.  I think I'm still going to try and save the front Y-pipe 'cause it is original to the car (just in care for down the road). 

Norsky38621.4484722222