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  #1  
Old January 20th, 2023, 07:50 PM
Troyport Troyport is offline
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Default exhaust downpipes

Hello everyone, first time post here. Hoping someone can help me. I have a 1968 GMC 2500 pickup. I know this is the wrong forum (1968) but no one else has been able to help, because I have the 351 V6. Looking for downpipes. Seemingly no one knows what will fit. I would really like to build a dual system myself, and not go to a custom muffler shop. Thanks for any help.
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  #2  
Old January 20th, 2023, 09:18 PM
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AZKen AZKen is offline
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Default Re: exhaust downpipes

Carefully define "down pipes" and we will help you. Manifolds? tail pipe? headers? Collector? Piece from manifold to muffler? Are you using the stock exhaust manifolds?
HOTRODJOHN has dabbled in this.

Last edited by AZKen; January 20th, 2023 at 09:32 PM.
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Old January 20th, 2023, 09:49 PM
Troyport Troyport is offline
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Default Re: exhaust downpipes

Thanks for the reply, sorry I was not clear. I have a stock 351 V6, stock exhaust manifolds (manifolds are NOT shaped like an I-beam) The exit of the manifolds point straight down, dumping out of the center (which I am pretty sure is the way all the manifolds point for the V6's. It looks like the pipes are attached with a flat gasket, and not a donut-style gasket, but I am not sure. I want a left and right pipe leading from these manifolds that terminate in a normal spot under the truck, facing towards the back, 2.5" diameter. Then I can add my own intermediate pipes, mufflers, etc.
It has dual exhaust now, but it is getting very rusty. And it looks like someone hacked-up a Y-pipe to do what I want to do, the welding is just hideous. I am not much of a welder, so my hope is to get proper downpipes then build from there with sleeve-style clamps. The truck is a 1968, so not even sure if what may fit a 60 - 66 would even work on my truck, but no one else has been able to help me, it seems like most people either have or swap in V8's. It is very functional now, so I don't want to pull it apart without a clear path forward. Thanks again.
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Old January 20th, 2023, 10:18 PM
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AZKen AZKen is offline
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Default Re: exhaust downpipes

There is no aftermarket piece. Your options are:
1. Do what that other person did.
2. Buy flanges and pipe and fabricate.
3. Find a friendly muffler shop,, take a manifold to them and ask what fits it, what parts are needed and if they will sell you the parts.
4. Have a friendly small muffler shop make you those two pieces.
5. Use the internet<<<<<<click on this as an example.
6. Contact HOTRODJOHN

I my self would do no. 4 for sure. I believe you are correct about flat gasket needed at that connection. I have a crossover that can be cut to supply the connection sections. PM for further.

Last edited by AZKen; January 21st, 2023 at 04:16 AM.
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Old January 21st, 2023, 02:55 PM
Troyport Troyport is offline
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Default Re: exhaust downpipes

Thanks for the reply. Option 4 probably makes the most sense. I have already talked to a local muffler shop who specializes in custom systems. Potentially the only concern I have is the mounting flange at the manifolds. If that is unique, I would hate to have him temporarily stalled with my truck apart. Can anyone direct me to those? Would like to have them for him to use. I don't know if the link you provided is correct. Thanks again
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Old January 21st, 2023, 04:13 PM
Troyport Troyport is offline
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Default Re: exhaust downpipes

I see these pipes for the V8, where it appears they attach to manifolds that point straight down. Would these work with flange modification?
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Old January 21st, 2023, 10:27 PM
Prowbar Prowbar is offline
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Default Re: exhaust downpipes

Quote:
Originally Posted by Troyport View Post
I see these pipes for the V8, where it appears they attach to manifolds that point straight down. Would these work with flange modification?
Maybe, maybe not. you need to route the pipes around the oil filter, which is a tight spot on the V6. Custom pieces are probably the way to go. You can cut up and re-weld the V8 pipes.
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Old January 21st, 2023, 11:40 PM
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Default Re: exhaust downpipes

As I said in my post, I can supply those sections/flanges by cutting them off a crossover I have.
Post your email in a PM if you want to discuss further.

The link was just a sample of using the internet.. The actual flange is a three hole pattern. Probably very unique to GMC V6.

Last edited by AZKen; January 21st, 2023 at 11:52 PM.
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  #9  
Old January 23rd, 2023, 01:34 AM
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AZKen AZKen is offline
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Default Re: exhaust downpipes

I have the downpipes for anyone who wants to build an exhaust. $25
$18 ship to lower 48
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Last edited by AZKen; January 23rd, 2023 at 10:43 PM.
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