exhaust tubing

[Douglas L.]

I know the 68-69 judging guide says the factory exhaust tubing was double walled but I'm having a tough time believing it. Does anyone have any pictures or personal experience that supports the info, maybe a picture of a cross section?

Thanks, Doug

[Edward J.]

Re: exhaust tubing

Doug, I worked as a GM tech for many years before going into business for myself and yes GM did have double wall construction exhaust pipes, once in a blue moon I used to see the inner wall of the pipe clasp and this would cause a power loss when driving., I have no pic.'s of the piping, but can tell you if you picked up todays replacement pipes and a original or GM replacement pipe there's a big difference in the weight.

[Joe L.]

Re: exhaust tubing

I know the 68-69 judging guide says the factory exhaust tubing was double walled but I'm having a tough time believing it. Does anyone have any pictures or personal experience that supports the info, maybe a picture of a cross section?

Thanks, Doug

Doug-------


I can tell you this, for sure: if it was actually double-walled, it was not double-walled all the way to the ends of the pipes.

[Donald H.]

Re: exhaust tubing

I remember seeing an exhaust pipe where the inner wall had collapsed and the outer wall had not. I took a while to troubleshoot that problem.

[Edward J.]

Re: exhaust tubing

I remember seeing an exhaust pipe where the inner wall had collapsed and the outer wall had not. I took a while to troubleshoot that problem.

Ya Don the first time I saw this was in the 70's and it will only happen to you once and then you know what to look for next time, Joe L. I cannot tell you if the all pipes where done with double walls but I would say the front pipe was and maybe the Mid pipe.

[Joe L.]

Re: exhaust tubing

Ya Don the first time I saw this was in the 70's and it will only happen to you once and then you know what to look for next time, Joe L. I cannot tell you if the all pipes where done with double walls but I would say the front pipe was and maybe the Mid pipe.

Edward-------


I have NOS examples of both the front and rear pipes. What I'm saying is that if the pipes were double-walled, then they were not double-walled all the way to the ends. The ends of the pipes show absolutely no evidence of being double-walled.

[Mark E.]

Re: exhaust tubing

Double-walled exhaust was not limited to Corvette. In the mid-70s, the inner wall of an exhaust pipe collapsed on my brother's 1970 Cadillac deVille. It took awhile for the dealer to figure out why the car ran poorly.

[Jim T.]

Re: exhaust tubing

Douglas, I removed the drivers side rear exhaust pipe and muffler as one piece from my 1968 many years ago. I kept the rear exhaust pipe and muffler together with the chrome tip attached on the muffler outlet. This assembly is still in my attic. I do remember in separating the rear exhaust pipe from the front exhaust pipe that the double walled rear exhaust pipe showed the two layers where it connected to the front exhaust pipe. I will send you a e-mail picture if you have to have it.

[Joe L.]

Re: exhaust tubing

Douglas, I removed the drivers side rear exhaust pipe and muffler as one piece from my 1968 many years ago. I kept the rear exhaust pipe and muffler together with the chrome tip attached on the muffler outlet. This assembly is still in my attic. I do remember in separating the rear exhaust pipe from the front exhaust pipe that the double walled rear exhaust pipe showed the two layers where it connected to the front exhaust pipe. I will send you a e-mail picture if you have to have it.

Jim-------


Attached are some photos of the forward end of some NOS GM 2-1/2" rear pipes. This is the end into which the forward pipes insert at the transmission crossmember. I can see absolutely no evidence here of any double wall construction.


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[Jim D.]

Re: exhaust tubing

Those "NOS" pics are of over the counter service replacement parts and obviously are not what was installed in production. I too have removed factory installed double walled exhaust pipes off a C-3.

[Joe L.]

Re: exhaust tubing

Those "NOS" pics are of over the counter service replacement parts and obviously are not what was installed in production. I too have removed factory installed double walled exhaust pipes off a C-3.

Jim-------


It is true that the rear pipes have part numbers not used in PRODUCTION. That's because in PRODUCTION the rear pipes were welded to the mufflers as an assembly and, consequently, the SERVICE pipes are shorter (to accommodate the extension on the SERVICE mufflers) and, thus, have a SERVICE-only part number. However, I HIGHLY DOUBT that the basic construction of the SERVICE pipes differ from the PRODUCTION pipes. There would have been absolutely no reason for GM to do this and I don't think they did.

However, the N-11 SERVICE assemblies were identical in part numbers to those used in PRODUCTION. Therefore, even if there was a difference in the standard exhaust rear pipes between PRODUCTION and SERVICE (and, to be clear, I don't think there was), the N-11 assemblies being of the same part number PRODUCTION and SERVICE, I can't see how it would even be possible for them to have different basic construction. I have NOS N-11 systems, too. Attached are photos of the forward end (the same views I pictured above) and they don't show any evidence of being double-walled.

As I said before, it's possible that these pipes are double-walled but, if they are, they are not double-walled all the way to the ends. If anyone has some original, PRODUCTION pipes, I'd love to see photos of the ends to see if they differ from what I've pictured.


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[Bill C.]

Re: exhaust tubing

i have stayed away from posting, just wanted to see where the post went...


My story....
all evolves around a 1972 with 454 4spd and 42K one owner miles (before I purchased in 2000)

long story short - car had a complete factory welded system on it. never touched.
mufflers completely shot on both side and rust on the long sections under the seats.

I pulled the system off, figured way to far gone to salvage. Served better as a pattern for when I would weld a complete NOS system together for the car.
so ..
after taking a BUTT load of pictures, I decided to cut up the system to see if the double walled pipe was for real or not.
and it was......
I cut the pipes about 1.5 back from the head pipe mount area and cut the pipe about 6" down from the rear of the muffler.
only place I could see evidence of the double walling was further down the pipe.

however, the NOS pieces I grabbed up, I very clearly remember seeing layered "pipe over pipe" all the way at the ends - just mid section pipes.
the head pipes looked normal in configuration on the ends.
I seem to recall the thickness of each layer of pipe to be significantly thinner than a normal piece of carbon steel pipe, but the combined thickness looked somewhat like standard CS pipe.

2x walled pipe is heavier the standard CS and when you thunk it with a wrench makes a dull sound.



now the bad news - my computer crashed and killed the HD a year or two after I finished the resto (2007) and I have nothing to
backup my facts....
LOL

swear I am telling the whole truth

[Paul O.]

Re: exhaust tubing

Here are some photos of over the counter GM pipes. As you can see there are 2 pipes both on the front pipe and rear pipe. Hope this helps.

[Joe L.]

Re: exhaust tubing

Here are some photos of over the counter GM pipes. As you can see there are 2 pipes both on the front pipe and rear pipe. Hope this helps.

Paul------


What about the forward end of the rear pipe----the end that I pictured in all of my photos?

Also, what is the total thickness of the tubing at the ends you have pictured?

[Paul O.]

Re: exhaust tubing

Joe

The rear pipe at the inlet and outlet ends are between .092 and .096. The header pipe at the swagged inlet is .079 to .082 the outlet end is .091 to .094.