Well, after years of owning 3rd gens, i thought i'd seen it all. I did several searches and didn't find anything. The exhaust shop said they'd never seen it in 20 years of working on cars. Apparently, our cars have double-walled pipe in the upper part of the exhaust. I had the cat and all the way back done 2 years ago, figuring i'd never have to touch the exhaust again. Until..... Last monday, the car literally bogged down and died. While at my mechanic's for an axle replacement (whole nuther story!) He looked at it and went, that front pipe has collapsed, and sent it over to the exhaust shop. THEY didn't belive him! Guy said he'd never seen that kind of collapse, ever. Well, they cut it open and guess what. The crossover pipe was SO collapsed, it basically had 2 pea sized openings in it for passing exhaust. And that was it. The inner piple had bulged out for like 8 inches down that pipe. Not rust either! Just total collapse. I've tried to figure out how to take pictures of it, but its hard to take pictures of the inside of a pipe! You kinda have to stick a flashlight down it to see it. Its really amazing...... SO heads up for those of you who haven't done the entire exhaust!!!!

 

I have seen that alot back in the '70's, if a pipe got a dent in it, the heat would cause the inner wall to expand and close off the flow.

So, no picture needed here, I have had lots of experience with that situation.

 

Yeah, in the 70s I used to replace pipes like those. I had forgotten all about double walled pipes!

 

What was the aim of the double wall?

 

To protect the starter and various other components from being cooked by the exhaust. very close quarters. Chevy found out later it really didn't help much....