I presume you are talking about a barrel nut. If so, insert the hex. Use some of the heat you don't have and the chisel and crush the sides onto the nut. Two people help it go better. If you get it started it will come right out if it is hot enough.
ARF

You guys are scaring me....... as I am about to cross the LOD [Line of Departure] in the next couple of days when my M&K 2/1 arrives.... and I commence the great exhaust overhaul >> remove the OEM heat exchangers and install SSIs and M&K 2/1.

Quest: What does the Dorki braintrust think of using an impact wrench on the exhaust nuts? I have a harbor Freight 18v job... maybe I can configure extensions and u-joints where I have a shot at the nut... What's the optimum technique > hit the nut fast and hard form the outset - or - a slow and steady application of force?

I tell ya > not real keen on getting under the car with a Propane torch...

Currently I'm soaking the nuts with PB Blaster.. been soaking for 3 days now..

Impact MIGHT work but you would have to control the pressure (likely around 25-30lbs). Your exhaust has been off in the last few years so shouldn’t really be a problem. Just use lots of PB Blaster and some heat and the nuts should come right off. In your case slow and careful should work just fine. It’s the ones that haven’t been loose since leaving the factory 20+ years ago that are truly problematic.

Grady Clay method. Take a left twist spiral extractor and grind the end down untill the end is the same size as the hole on the barrel nut. Heat the nut and hammer your custom extractor it in some and crank on it. The nut should ether come loose or split down a side. The extractor will dig into the insides and try and spread the nut apart. If you have access cut a slit down one side of the nut. Even a small slit part way through will act to help split the nut.
Non VSR impact gun will ether 1. back the nut off. 2. strip the hole in the nut or 3. snap off the stud. #2 and 3 suck and #3 truly sucks.

If the nut is all F-ed up and or the stud is sticking into the nut you can stick an allan tool in the best you can and MIG weld the tool to the nut. The heat of welding will help loosen the nut and the tool will not slip. Grind the weld off the tool and remove the nut when done. You can also just use some 3/8 square bar stock with the end ground down to roughly fit and pitch the mess when the nut is removed or just saw the nut off.

I too am facing this one eventually [have SSIs and 2 in 1 out SS sport] and think I'll try the heat [MAPP b/c don't have Oxy] / PB blaster / dremel / extractor route.

NOT looking forward to this one.

Maybe I'll pull hte motor 1st to have better access on the stand.

hmmmm...

I did the SSI thing many years ago on my old '73 (still a ~20 year old car at the time), and it wasn't too bad. I used the weird bent wrench (from my previous post), a couple of different craftsman u-joint-socket combos, and an allen driver (really a standard allen wrench with the right angle cut off so you could use an 8mm socket on it).

I remember just being gentle with the nuts, and if they started to resist, backing off and turning them the other way. Back and forth. Just hand tools, no heat. I ended up taking out about half of the studs, but I didn't break any. Put new studs in using blue loctite and the double-nut trick, torqued the new nuts to spec and away we go.

Maybe I just got lucky?

I think so ...

When I put on my SSI's in '86 I broke two studs flush with the case. I had to drill them out while lying on my back on the ground since I didn't have a garage at the time. Not fun at all. :bang: In retrospect it would have been easier to drop the engine.

Are copper nuts acceptable for use on 911 exhaust? They sure are easier to remove later on.

Can’t think of any reason why not, except cost. But the couple bucks a piece for the self locking manifold nuts would be well worth it down the road. You can actually get one mm smaller across the flats than normal too, which helps some. 931 part number ~$3 each..
I’ve broken my share of studs removing heat exchangers. But have seldom had trouble if HEs had been removed before. Its lots easier on a stand ;) Also, cutting the none barrel nuts off is IMO often lots easier.
The off set wrench that came with my first set of SSIs made it a lot easier too. They’re in trouble too if I remember who borrowed it some years ago and didn’t return it!

BTW, if your old HE exchangers are rusted threw why not just cut them off first? Makes access to all the nuts much easier.