After failing to get my broken exhaust fixed and I now in the process of fitting a new cat-back exhaust.

The exhaust came with a gasket to go between the pipe and the catalyst. Do I also need to apply some sort of sealant between them ? Also, the exhaust has a join near the back box with a clamp to hold it together, do I also need some sort of sealant there ?

I'm not an expert but I believe you can (should?) use exhaust assembly paste on the gasket and possibly on the clamped pipe too. I think you just apply it liberally like grease and it sets when heated.

By the way, I did look on yell.com on Sunday to see if they had anyone that could help but it didn't really shed any light :-( Did you drive it back anyway?

Gareth

Thanks. I might not been needing the assembly paste after all. It looks like the 1997/1998 Mk1 MX5/Miata might have a longer cat than other years. Meaning that my nice new exhaust won't fit without being cut down, which makes it a job for someone else...

I didn't drive it back, I had the AA recover me back home. If I had driven another 160 miles my bumper would have been a puddle of black plastic...

Ditch the cat and find a friendly MOT place.

It would appear that ditching the cat wouldn't help me any. If I have a long cat apparently I also have a shorter than normal down pipe, meaning that the standard cat replacement pipe wouldn't fit either.

If do have a long cat then I think I'll have to get the exhaust chopped and the flange welded back on. I don't know what the implications are when I need a new cat though as I don't know if Mazda actually sell the long cat as a spare. The various MX5 parts sites definitely don't sell two different cats.

I know there are other reasons for wanting to ditch the cat, but I'm not that desparate for another 3hp...

you wont need to treat the exhaust gaskets, they go on dry.
the goop for the pipe to pipe slip fit is not a bad idea, but not a must either.

What, not even when the gasket is metal, between two metal components ?

nah, just wedge it in there and bolt em together

BTW...
use new copper exhaust nuts (self locking type) on any studs / bolts.
not the 'nylock' ones.......they melt (:

Just another agreement, we assemble about 25 engines each day here at the Diesel shop, and it's all a thin metal gasket between to cast iron pieces (head and manifold).

Get some paste if you want it, but you're almost certainly not going to need it (assuming the gasket itself is new).

Oh, and use some copper grease on the nuts so that you can get them undone again in the future if you need to

Ah, my Edelbrock system has some fibrous "doughnuts" which my mechanic spread paste over when he put it back on (after welding half the darn floor up!)

Gareth

nah, just wedge it in there and bolt em together

I agree, I recently put an aftermarket exhaust on my car, just slap the gasket in there and torque to the correct amount, you should be fine.