LT1-EXHAUST

[Mike G.]

did they have an off road exhaust option on the 70 lt-1? were the mufflers date stamped?

[Joe L.]

Re: LT1-EXHAUST

m------

There was no "off-road" exhaust option for 1970. The last year for "off-road" exhaust was 1968 and no side exhaust was available that year. The last year for side exhaust was 1969. In the latter case, mercifully.

[Terry M.]

Re: LT1-EXHAUST

No date stamp on any of the mufflers in 1970-1972. For any of the engines.

[Mike G.]

Re: LT1-EXHAUST

thanks for the help. that makes it easy.

[Harmon C.]

Re: LT1-EXHAUST

If you are interested in the date you must be thinking about judging. Original mufflers had other marks not on todays replacements so it's not that easy to be 100% correct or even close.

Lyle

[Mike G.]

Re: LT1-EXHAUST

true, i am looking for nos stuff first. i have the mufflers as 3943386 and 3943385. i would guess the pipes are hard to tell repo from original but i will attempt to find them too.

[Joe L.]

Re: LT1-EXHAUST

m-------

First of all, SERVICE mufflers and pipes are configured differently than PRODUCTION pieces. The core mufflers and pipes are the same, but they are configured differently for SERVICE. The difference involves the fact that SERVICE mufflers (except N-11) have an extension welded to the forward end of the muffler. PRODUCTION mufflers include the complete rear pipe welded to the muffler.

The rear pipes used in PRODUCTION (and, welded to the muffler) are longer than the SERVICE pipes. The SERVICE pipe's shorter length is set to accommodate the extension on the SERVICE muffler.

So, even if one obtains NOS SERVICE mufflers and NOS rear pipes, one is not going to achieve original PRODUCTION configuration when ones uses these parts as-is. It's going to be obvious to anyone that the configuration is not as original. The slip or "bell" joint present in the SERVICE configuration but not in the PRODUCTION configuration is a "glaring tip-off".

As far as the rear pipes go (i.e. trans crossmember-to-muffler), I have yet to see any reproduction or replacement pipe that is configured anywhere near original. The original pipes, PRODUCTION or SERVICE, were DIE-FORMED. They were not "bent", mandrel or otherwise. There is NO WAY to achieve the die-formed configuration when the pipes are manufactured using any sort of bending process.

Supposedly, Gardiner Exhaust is coming out with mufflers and pipes for Corvettes which are "true-to-original" in configuration. We'll see. However, if they use any sort of manufacturing process other than die-forming, they will not achieve original configuration. They may be able to duplicate SOME ASPECTS of original configuration unavailable until now, but they will NOT be able to achieve completely original configuration. Period.

[Phil P.]

Re: LT1-EXHAUST

joe,you have an excellent point---correct me if i'm wrong but the c3 pipes were double wall as well---or am i thinking of other car makers---when i was out of high school i worked at a midas store and ran into several exhaust pipes where the inside tube had collapsed causing major back pressure---anyhow if c3's had double wall pipe re-pops would seem to be very expensive---just my 2 cents ,phil

[Joe L.]

Re: LT1-EXHAUST

PHIL------

I have heard the "double wall" contention many times. However, I have quite a few NOS pipes here and I can find no evidence of their being "double-walled". If one looks at the end of the pipes, the pipe wall appears to be monolithic. It may be possible that somewhere "inboard" of either end a "double wall" section begins. I seriously doubt it, but I suppose it's possible.

I think that the term "double wall" may derive from the fact that the THICKNESS of the pipe material is double that of "standard" pipes. Beyond that, what would be the advantage of using a "double wall" (presumably meaning a "tubing-within-a-tubing") rather than just use "monolithic" tubing of a thickness equal to the sum of the thicknesses of 2 tubes used in a "double wall" configuration?

[Phil P.]

Re: LT1-EXHAUST

joe'i know what you mean about finding double wall on a given tube---the midas re-placement tubes were much heavier than the less expensive tubes bent using bend cards---as well, the double wall was not easily evident on the re-placement tube---also the tubes i cut through were most assuradly double wall, i'm not sure if they were gm or ?---i kinda think chrylser used these but not sure---i'll get in touch with some old buddies that might remember---thanks,phil
p.s. i have an original 72 lt1 with org. exhaust and i will try to borrow a tube thickness gizmo used for nhra roll bar thickness and see what i come up with----------------

[Terry M.]

Re: LT1-EXHAUST

I don't know the reason for the double wall, but I would speculate that it made bending easier than a single twice as thick pipe. I have seen enough holes worn in the pipes, especially under the differential where they tend to sag, that I am a believer in the double wall. Lift a few, or carry them from one end of the swap meet field to the other, and you will be convinced as well.

That feature changes the tone also. One of he many reasons reproduction exhaust systems never sound like OEM. At the advanced judging schools I try to get an original exhaust system, when available, on the lift so that those in attendance will have the chance to both hear and see what one looks like. Regrettably, this is becoming harder and harder as time goes on.

[John H.]

Re: LT1-EXHAUST

I don't know the dates and applications offhand, but the double-wall pipes were used beginning in the very late 70's on some GM cars, only on the front exhaust pipes (forward of the catalytic converter), to retain more heat in the exhaust gases to shorten the "light-off" time for the converter, to pass the cold-start portion of the emission test. This portion of the test has become much more severe since then, which is why the C5-C6 Corvettes have four converters, with the front two only inches away from the exhaust manifold outlets, to "light them off" much faster at cold start.

[Harmon C.]

Re: LT1-EXHAUST

Terry

I have some used tear off pipes that I'm sure are double wall because one wall is rusted off. If I can find them I will cut a section off for show and tell.
Lyle

[Terry M.]

Exhaust show & tell

If you find them by Florida, I would be pleased to use them there.

[Jim T.]

Re: Exhaust show & tell

Years ago I removed the drivers side rear pipe and muffler. I held off doing this although I had replaced the passengers side many years before. The removed rear tailpipe is double walled where it connects to the front pipe. Had a good job in separating the rear pipe from the front pipe and acutally bent back two layers of metal and discovered that the pipe was double walled. I would of left it on for more years of use although rusty on the outside it was in very sound shape, anothe reason was that the muffler was nothing but an expansion chamber, nothing on the inside, and the chrome extension rusted to the mufflers pipe. Really liked the sound of that muffler, but it developed a crack near the inlet and was leaking exhaust. It is of no use, but I had room in the attic so I kept it.