About a year ago (really don't know when) my catalytic converter split and I rushed to buy a replacement header. I went with a cheap (<$200) M2 Performance aftermarket model. The fit was not perfect.
The biggest problem was the downpipe seemed just a tad short to match up with the stock cat-back exhaust. The gap was about 3/16" and could be squeezed together of course with the nuts.
After driving around a bit the exhaust separated, one of the nuts came off and the gasket blew. I couldn't find any thicker gaskets so I bought a small sheet and cut out two gaskets and JB Welded them together. That lasted a good while... but now THAT gasket has blown and the nut came off (I don't know which happens first).
I need a quality gasket that is hopefully 1/4" thick or thicker. I remember reading something somewhere relating to an aftermarket MINI exhaust about a thick gasket but I can't find it. I also am trying to find a way to keep that nut from coming off. Can anyone help?
It's an '06 R53

 

Lock washer use? Try a lock washer and stover nut too.

Jeremy

 

Stover nut... I'll have to look into that. I still need to find a gasket of proper size. I don't know if the gasket is blowing because the nut comes loose or if the nut comes loose because the gasket blows.

Luckily I found a bolt around the garage that is the same size as the one on the exhaust so I can go see what size it is at Lowe's.

 

You need a spacer plate to take up that extra gap, then use two gaskets on either side with longer bolts, nuts and lockwashers. The spacer plate can be obtained at any good muffler shop.

 

That's a good suggestion NC. I'll definitely look into it.

 

I found the site I was looking for! It's an installation guide for putting a header on an R53.
http://www.billswebspace.com/MCSHeader.htm
That's what I followed for my install. I can't tell what that thick gasket piece is. The fel-pro one looks like a normal thickness.

 

So I ended up cutting off the flange from my old broken header to use on this one as a spacer.
I bought some longer bolts at the hardware store. I took down the cat-back factory exhaust and pounded the hell out of the bolts to get them out of the flange. They wouldn't budge. I assumed they are pull-in bolts. I soaked in in PB Blaster a few times and hammered around the flange but nothing would help. I was starting to flatten the tips of the bolts so I gave up.
I ended up bending back the exhaust hangers so it would naturally sit further forward. This seemed to work out pretty well. I was able to use a standard gasket and some copper gasket maker to seal it up. All the good ideas come to mind AFTER the hard work. I used locking washers so these nuts should stay on this time.