Long story short, because of the crappy way the exhaust on the Miata has been dealt with over the years, cutting it apart and removing everything including the header seemed like the best option.
I'll slap a head on it and have an exhaust built that I can use when I eventually VVT swap it.
Back on point, all the nuts or nut/stud combo, came out of the head with no drama. I'm not going to bother replacing the studs that didn't come out, but I will replace the 2-3 that did.
I am correct in thinking I SHOULD replace the nuts, but Mazda is AWFULLY proud of them at ~$9 EACH!
So, can I reuse the existing ones? Is there a cheaper place to get the nuts? Thoughts?
I re-use non-re-usable nuts all the time. No you shouldn't, and yes you probably can get away with it.
Any idea what's special about these?
On my ancient BMW, they're flattened (crushed into an oval) to make them grab the studs and not loosen.
If your have that sort of mechanical deformation and still appear to have a significant amount of it... Well, that would seem to suggest bravenrace's idea that you can probably get away with it.
The BMW ones also appeared to have a coppery coating. That may have been an anti-seize, and if that's all scraped off (if yours ever had such a coating), you may lose more than 2-3 studs next time...
$9/nut is pretty... well... nutty.
Are they special? Im sure, Fastenal, McMaster-Carr, TSC, any good hardware store, etc. probably has them.
No idea other than Mazda's asking price.
I don't care about next time. I'm just hoping this motor stays together for this HPDE season, then it's going to be gone for a VVT. 
What size are the nuts? I have a Mazda BP engine that I'm rebuilding and the studs are 10 MM if I remember. I can't see where it would be that hard to find new nuts. VW likes to use copper nuts as they won't seize and if they do they are soft enough so that cutting them off is not a problem.
Fastenal, they can't be that 'spensive
My shop keeps a big bin of various size copper pinch nuts for exhaust. I'm sure we pay too much from WURTH for them, but I don't see how any hardware supplier wouldn't have proper (cheaper) replacements.
BTW- I re-use them all the time on exhaust stuff with no issues.
jimbbski wrote:
What size are the nuts? I have a Mazda BP engine that I'm rebuilding and the studs are 10 MM if I remember. I can't see where it would be that hard to find new nuts. VW likes to use copper nuts as they won't seize and if they do they are soft enough so that cutting them off is not a problem.
I think 14mm. But I'm too lazy to walk out to the garage right now.
I could spill my drink.
hit the "Help!" section of your favorite parts store and get new studs/nuts.. broken exhaust fasteners make me sad, and the oems charging that damn much for a nut makes me even sadder...
I just got to the local hardware store and get grade 8 stainless steel nuts and stainless steel lock washers. Done this for several exhaust headers with out issue. I use high temp anti seize and although it seems to burn off I have never had a problem getting this undone later.
I've had the exhaust manifold on and off my Miata quite a bit -- I'll reuse the nuts once or twice, but not much beyond that. They're oval-shaped mechanical locknuts ("stover", I think they're called) and the second time you put them on you can tell that they go on with a lot less effort than the first time, suggesting they aren't locking as well. IIRC you can save a few bucks getting them from Mazdaspeed instead of the local dealer.
They're M10 and take a 14mm wrench (I forget the thread -- probably 1.5). I don't think non-locking nuts would be a good idea and the only locknuts my local hardware store sells are nylock, which obviously doesn't work too well on an exhaust manifold. :) I wouldn't trust lockwashers for an exhaust manifold, either.
I've got a turbo on it, so they probably see more heat than usual, however.
