# Stock '68 exhaust manifold outlet diameter?



## wishihaditback (Jun 9, 2011)

Unless i'm missing it in my '68 chassis manual somewhere, i can't seem to find the stock (non-RA/HO) exhaust manifold outlet diameter. 2.25 or 2.50, or none of the above? Thanks.


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## PontiacJim (Dec 29, 2012)

They are 2". From Garner Exhaust Systems - 1968 GTO Exhaust Systems - Gardner Exhaust Systems - 1968 GTO Exhaust Sytems by Gardner

*1968 GTO*
The 1968 GTO has the distinction of introducing probably the most unique of any GM Muscle Car exhaust systems. The 68 GTO was available with four different systems. The Std duty manual cars received 2" head pipes and 2 1/4" tail pipes, while the HO manual cars were outfitted with 2 1/4" head pipes and 2 1/4" tail pipes. The automatic cars used the same head pipes as the manual cars but a tail pipe that probably would get most employees fired if they pitched it to R&D today. This tail pipe was a 2 1/4 tail pipe that split into two 2" pipes one allowing the gases to exit out the back of the car the other pinched shut just above it. Our 1968 GTO exhaust systems come with the correct head pipes, correct unequal length mufflers, correct tail pipes, yes even the tuner tail pipe for the automatic cars, correct hangers, correct GM style clamps, correct flanges, installation instructions, diagrams and sealant, chrome extension which made use of a GM adapter pipe to correct the geometries of the system are an option, as well as a concours show pkg. to keep the system looking clean and new.

Ask about our Turbo Mufflers for those who want the system to look original but just have to have a little more noise!


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## wishihaditback (Jun 9, 2011)

Thanks for your helpful response! The website was very informative as well.


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## Pinion head (Jan 3, 2015)

Tonight, another night going through more parts, getting ready for moving everything. Was boxing numerous Pontiac V8 exhaust manifolds. 
-Measured the outlet of a '69 and a '71 standard log style A body drivers side Abody manifold. Each manifold, the opening of the outlet was only 1.75". 
-Also ck'ed a pair of original '69 RAIII GTO ex manifolds, the opening of the outlet was 2.25". Have a set of RAII GTO manifolds and several pair of '70-71 roundport manifolds to ck... more later this upcoming week.


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## wishihaditback (Jun 9, 2011)

Thanks for that info Pinion head.


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## deanhickey (Apr 6, 2015)

Just quick question, what are the benefits if any of of the pinched off tailpipes for the automatic cars, were they just for tone?


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## O52 (Jan 27, 2019)

They were used as tuned resonators.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Just quick question, what are the benefits if any of of the pinched off tailpipes for the automatic cars, were they just for tone?


Not sure I have seen the tailpipes you speak of. My brother's '68 Bonneville had factory resonators which was part of the tail pipe assembly. These are essentially a small muffler that reduced the exhaust sound over what the mufflers did. I don't know how it was decided which cars got them and which ones didn't. My brother got rid of them when he put new tail pipes on without the resonators.

Here is what Chevy offered, a chambered pipe that stood in for a muffler. Basically a straight pipe with the crimped sections to dampen the sound waves. Here is a business that offers them and you can read a little about them. I don't know how they 



Classic Chambered Exhaust Inc. - Products


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## deanhickey (Apr 6, 2015)

PontiacJim said:


> Not sure I have seen the tailpipes you speak of. My brother's '68 Bonneville had factory resonators which was part of the tail pipe assembly. These are essentially a small muffler that reduced the exhaust sound over what the mufflers did. I don't know how it was decided which cars got them and which ones didn't. My brother got rid of them when he put new tail pipes on without the resonators.
> 
> Here is what Chevy offered, a chambered pipe that stood in for a muffler. Basically a straight pipe with the crimped sections to dampen the sound waves. Here is a business that offers them and you can read a little about them. I don't know how they
> 
> ...


Hi Jim, I probably used the wrong description, on the 68 automatic trans exhaust the tail pipe split into two branches. One was left open like a normal exhaust and the other was crimped shut. I was wondering if the second crimped shut tail pipe had another function other than effecting the sound of the exhaust? it should be visible in the attached picture.
Thanks,
Dean


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Hi Jim, I probably used the wrong description, on the 68 automatic trans exhaust the tail pipe split into two branches. One was left open like a normal exhaust and the other was crimped shut. I was wondering if the second crimped shut tail pipe had another function other than effecting the sound of the exhaust? it should be visible in the attached picture.
> Thanks,
> Dean



Hmmm. I think what I see are 2 different rear tail pipe section choices. I see a tailpipe with the "crimped" end which looks like a deflector, not crimped off as in closed. Then I see the other tail pipe section below it and it uses the chrome '68 exhaust tips.

So I think what you are looking at are 2 options offered by the exhaust maker, 1 being the deflector - which directs exhaust down at the ground to save your bumper from deteriorating due to the chemicals in the exhaust fumes, and the other being factory below the bumper.

Couple of deflectors below. The Packard tip shows how the end is closed off to deflect the exhaust gases down to the ground.


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## integrity6987 (May 10, 2017)

it might be that the flattened ends are needed for the manufacturing process and intended to be cut off before adding on the beautiful chrome tips.


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## deanhickey (Apr 6, 2015)

PontiacJim said:


> Hmmm. I think what I see are 2 different rear tail pipe section choices. I see a tailpipe with the "crimped" end which looks like a deflector, not crimped off as in closed. Then I see the other tail pipe section below it and it uses the chrome '68 exhaust tips.
> 
> So I think what you are looking at are 2 options offered by the exhaust maker, 1 being the deflector - which directs exhaust down at the ground to save your bumper from deteriorating due to the chemicals in the exhaust fumes, and the other being factory below the bumper.
> 
> ...


I called Gardner exhaust and he explained to me that all 1968 GTO automatic Transmission cars had this exhaust system. If you look carefully at the picture you will see that there are 2 tailpipes joined together on each side, the top being the crimped and the bottom being open and exiting under the bumper. The chrome horn attaches to the bottom open pipe. He believes that the top closed pipe was for acoustic effects. the top crimped pipe would not be visible under the car. Probably useless trivia, but I leaned something today.

I have to say Mr. Gardner was very pleasant and answered all my questions.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> I called Gardner exhaust and he explained to me that all 1968 GTO automatic Transmission cars had this exhaust system. If you look carefully at the picture you will see that there are 2 tailpipes joined together on each side, the top being the crimped and the bottom being open and exiting under the bumper. The chrome horn attaches to the bottom open pipe. He believes that the top closed pipe was for acoustic effects. the top crimped pipe would not be visible under the car. Probably useless trivia, but I leaned something today.
> 
> I have to say Mr. Gardner was very pleasant and answered all my questions.


Wow, thanks for going to that length to clarify. I would have never imagined that the pipes were split like that. I have never heard, not seen, anything like it. I knew about the resonators on the rear tail pipes.

The more you learn, the more you realize you knew less.


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## deanhickey (Apr 6, 2015)

PontiacJim said:


> Wow, thanks for going to that length to clarify. I would have never imagined that the pipes were split like that. I have never heard, not seen, anything like it. I knew about the resonators on the rear tail pipes.
> 
> The more you learn, the more you realize you knew less.


to get that little piece of originality will set you back north of 400.00. I think I will go with a normal setup.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> to get that little piece of originality will set you back north of 400.00. I think I will go with a normal setup.



No doubt. I think I can live without trying to achieve a 100 point restoration.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> to get that little piece of originality will set you back north of 400.00. I think I will go with a normal setup.


Had to check out the 1968 Shop Manual. Found the drawing of it in the exhaust section. It is called a "tuner pipe." Who knew? LOL


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