Help with Identify Exhaust Pipes.....JM states

[Rick B.]

Hoping to get some clarity on original Big Block GM 2-1/2"standard exhaust (Not N11's)I have researched the forum on this topic and there is much info, Yet, specifically with regard to the Mandrel bends did not see the area covered deeply. The JM states

65 JM says"consist of mild steel tubing with mandrel-bent curves. Inspect all exhaust systems for the presence of reduced - section areas or ridges in the bend areas."66 JM says"consists of mandrel-bent mild steel tubing w/ no reduced section areas or changes in diameter. Mild ridges may be present."

[Rick B.]

Re: Help with Identify Exhaust Pipes.....JM states

More pics for comparisons


IMG_0704.jpgIMG_0707.jpg

[Joe L.]

Re: Help with Identify Exhaust Pipes.....JM states

Hoping to get some clarity on original Big Block GM 2-1/2"standard exhaust (Not N11's)I have researched the forum on this topic and there is much info, Yet, specifically with regard to the Mandrel bends did not see the area covered deeply. The JM states

65 JM says"consist of mild steel tubing with mandrel-bent curves. Inspect all exhaust systems for the presence of reduced - section areas or ridges in the bend areas."66 JM says"consists of mandrel-bent mild steel tubing w/ no reduced section areas or changes in diameter. Mild ridges may be present."

Below are pics of two rear SERVICE exhaust pipes for comparison. So the questions are1) What are Mandrel Bend curves? Are they "ridges" or smooth bends?2) Have Mandrel Bent curves been seen for Production and Service rear pipes? — should the ridges be present (if yes see #3)3) Note the difference in ridges between the two pipes......Which has been seen as typical? 4) Do they both appear to be GM? Note the difference in pronunciation, quantity and location.BTW. the right pipe is said to be an original GM piece and the left is a used unknown.Thanks for the help

Rick------


I don't think that any original GM pipes, PRODUCTION or SERVICE were mandrel-bent. Among other things, mandrel bending would be a slow process to manufacture pipes in volume. I believe that all GM pipes were die-formed and I think that's why all the reproduction sources have such a hard time making a truly accurate reproduction. Creating the dies to do it as-original would be prohibitively expensive considering the size of the market. So, other pipe bending methods are used and they just don't create a pipe with all the nuances of original configuration.

The SERVICE rear pipes of course differed from PRODUCTION due to a length difference. However, they were otherwise generally the same. With SERVICE pipes, though, there is another variable. That variable is WHEN they were made and by what supplier to GM. Most of the Corvette pipes were made by Walker. However, some were made by Arvin. In any event, over time various facets of their manufacture may have changed which may account for the sort of differences you see in the pipes you have.

[Rick B.]

Re: Help with Identify Exhaust Pipes.....JM states

Joe, pretty clear, excuse the elementary nature of the question but

Is this mandrel bend detail a smooth bend, or is it the bends with ridges? or am i way off understanding...

What about part number stamping? the NOS pieces in the pics are stamped with 497/498 number.(Have yet to find them on the used ones)
....Do you think stampings are only on Original GM service pieces and other manufactures would not have them?

thanks Joe!!

[Joe L.]

Re: Help with Identify Exhaust Pipes.....JM states

Joe, pretty clear, excuse the elementary nature of the question but

Is this mandrel bend detail a smooth bend, or is it the bends with ridges? or am i way off understanding...

What about part number stamping? the NOS pieces in the pics are stamped with 497/498 number.(Have yet to find them on the used ones)
....Do you think stampings are only on Original GM service pieces and other manufactures would not have them?

thanks Joe!!

Rick-----


I think that a mandrel bend will be a lot smoother and ridge-free than GM pipes.

I have not seen the part number on all GM pipes. Some have them and some don't. In any event, original PRODUCTION pipes will not have the 497/498 numbers as those are SERVICE-only part numbers.

No other manufacturer could legitimately place the GM part numbers on parts they sold through their own parts channels. However, once-upon-a-time they could and did supply exactly the same pipes through their own parts channels. Could some of these pipes have inadvertently included the GM part number? Very possible. I've seen it happen on other kinds of parts.

Neither Walker nor Arvin have supplied the same pipes as they made for GM through their own parts channels for MANY years, so don't go out and buy Walker or Arvin and think you're going to get the GM-configuration pipes.

Did these major manufacturers once supply the same (or, nearly the same) mufflers through their own parts channels as they did to GM? Yes, they did. However, not all the mufflers they supplied through their own parts channels were the same. They had several different LINES of muffler products. Only their top-of-the-line was the same as OEM and those were not all that popular due to cost so you rarely find them today. There were slight differences, though, involving the embossments and the type of galvanized material used for the muffler shell. Size, internal configuration and sound were IDENTICAL. Have I ever found any of these? Of course.

[Terry M.]

Re: Help with Identify Exhaust Pipes.....JM states

Just so you can see what mandrel bent pipes are like:

http://www.mandrel-bends.com/catalog/mandrel-bends-34/

With these pictures in mind it might be worth while asking folks who use the term "mandrel bent" if this is what the really mean.

[Dick W.]

Re: Help with Identify Exhaust Pipes.....JM states

Note the inside of the bends on the mandrel bent pipes do not have a reduced diameter

[John H.]

Re: Help with Identify Exhaust Pipes.....JM states

The term "mandrel-bent" is generally mis-used by folks who don't understand the actual manufacturing process and see it in print regularly in various hot rod magazines; it was NEVER used in any volume production exhaust pipe manufacturing process.

As Joe noted, production exhaust pipes were made using ordinary pipe bending dies, sometimes followed by shaping dies for areas that needed localized alterations/flattening. Chevrolet did make some of their own pipes (not for Corvettes) at the old Flint Manufacturing plant downtown by the river; I was there one day to observe the process while on an Impala quality problem mission, and watched the workers actually bending the pipes. They were all on piece-work, and the priority was to make the numbers so they could leave early; their quality checking fixtures were made of WOOD.

The diagram below shows how actual mandrel-bending tooling operates; during the bending process, a flexible shank-mounted lubricated steel mandrel the same OD as the ID of the pipe is drawn through the pipe so the pipe diameter isn't altered in any way and remains perfectly round. This is a slow process, not suitable at all for volume production, and wasn't used by GM or their exhaust pipe suppliers.


MandrelPipe.jpg

[David L.]

Re: Help with Identify Exhaust Pipes.....JM states

I have not seen the part number on all GM pipes. Some have them and some don't. In any event, original PRODUCTION pipes will not have the 497/498 numbers as those are SERVICE-only part numbers.

Joe,

Back in the 1980's I bought a pair of used 1964-1965 Corvette 2" dia. exhaust pipes in Carlisle, PA. One pipe is stamped "3849868" at the back end while the other is not stamped. I bought the pipes primarily because the heat shields were still attached and in good condition. The 3849868 part number appears in the 1965 Corvette AIM as well as in my 1964 & 1965 Chevrolet Parts Catalogs (Oct. 1963 & Oct. 1964). I have always assumed that they were originally installed on the assembly line. Are they actually service replacements?

Dave

[Joe L.]

Re: Help with Identify Exhaust Pipes.....JM states

Joe,

Back in the 1980's I bought a pair of used 1964-1965 Corvette 2" dia. exhaust pipes in Carlisle, PA. One pipe is stamped "3849868" at the back end while the other is not stamped. I bought the pipes primarily because the heat shields were still attached and in good condition. The 3849868 part number appears in the 1965 Corvette AIM as well as in my 1964 & 1965 Chevrolet Parts Catalogs (Oct. 1963 & Oct. 1964). I have always assumed that they were originally installed on the assembly line. Are they actually service replacements?

Dave

Dave-----


The forward pipes are the same PRODUCTION or SERVICE. However, I don't find part number 3849868 as either the PRODUCTION or SERVICE part number. So, if the number is 3849868 it must represent something other than the part number for the complete pipe assembly. Perhaps, the part number for the pipe less the flange.

[Rick B.]

Re: Help with Identify Exhaust Pipes.....JM states

Note the inside of the bends on the mandrel bent pipes do not have a reduced diameter

Guys thanks for the response

I would be one of those guys not steeped in manufacturing so i may not know what i am asking.

Are the ridges I see a result of a Mandrel Bend? or a smooth result with no reduced diameter.
If I am reading correctly in this post, they have nothing to do with one another and in order to achieve a mandrel bend would be cost prohibitive...Yes?
Interesting....JM states this Mandrel bent curves were used for exhaust pipes....an inconsistency in the JM?

Thanks again, always appreciate reading your posts.

R

[John H.]

Re: Help with Identify Exhaust Pipes.....JM states

Interesting....JM states this Mandrel bent curves were used for exhaust pipes....an inconsistency in the JM?

Rick -

Yes, the JM should be revised; folks not familiar with the pipe manufacturing process are incorrectly using the term "mandrel-bent". Pipe-bending manufacturing tooling in the 60's was pretty much the same as the machine you'll find today at any franchise muffler shop - just heavier-duty.

[David L.]

Re: Help with Identify Exhaust Pipes.....JM states

Dave-----


The forward pipes are the same PRODUCTION or SERVICE. However, I don't find part number 3849868 as either the PRODUCTION or SERVICE part number. So, if the number is 3849868 it must represent something other than the part number for the complete pipe assembly. Perhaps, the part number for the pipe less the flange.

Joe,

GM # 3849865 and 3849866 (listed as "3849865-66") are listed in the 1965 Corvette AIM (UPC 8, sheet A2) as well as in my 1964 & 1965 Chevrolet Parts Catalogs (Oct. 1963 & Oct. 1964). I rechecked the stamping on the pipe and it is "3849868". I believe that you might be correct thinking that the part number is for the pipe less the flange or it could be a mistake by the manufacturer.

Dave

[Bill S.]

Re: Help with Identify Exhaust Pipes.....JM states

One other point to consider when talking about OEM exhaust pipes, GM used a double wall pipe for original equipment exhaust systems. The double wall pipe was also available as the service part replacement. The double wall pipe was actually a pipe in a pipe. If you hacksaw an original exhaust system you can see the seam between the two layers of pipe. This made the OEM exhaust last a fairly long time, reduced noise, and made the dealer replacement pipes twice as expensive as the pipes available at the auto parts store. You can tell OEM pipe from aftermarket pipe by its thickness. The OEM stuff is a lot thicker and heavier.

[Terry M.]

Re: Help with Identify Exhaust Pipes.....JM states

Bill -- Back in the days when swap meets were really that (pre-eBay) one could easily identify OEM pipes simply by weight. But that was then,a nd this is now.

FWIW: The original header pipes for my 1970 (2.5 inch small block) have part numbers stamped onto the OD of the pipe at the rear (as installed) of the pipes. I would have to do some hunting to find those numbers, but I do believe I recorded them someplace, and I believe they matched the header pipe part numbers shown in the AIM. That's my story & I am sticking to it.