Need a new exhaust

1987chevybad · Jan 19, 2019

My 85 350/th400 k30 dump truck needs a new exhaust, the headers are rotted out and the muffmuff are pretty much non existent.

Not really ideal for a plow/dump truck. Whats a dedend quality exhaust for the money? Should I get headers again or go back to manifolds. I really couldn't find a new y pipe for it, were all k30s true duals or am I not looking hard enough? Thanks

chengny · Jan 19, 2019

1987chevybad said:
My 85 350/th400 k30 dump truck needs a new exhaust, the headers are rotted out and the muffmuff are pretty much non existent.

Not really ideal for a plow/dump truck. Whats a dedend quality exhaust for the money? Should I get headers again or go back to manifolds. I really couldn't find a new y pipe for it, were all k30s true duals or am I not looking hard enough? Thanks

85 & 86 K30's (as well as K20's with the HD5/FED emissions package) got really nice exhaust systems. I'm on my third 86 - two were 20's and my current is a 30 - and they all have had dual 2 1/2" pipes. They were all over a certain GVRW (8500 lb. IIRC) and so they were essentially free of most emissions controls. No cats, no O2 sensors, etc. They had two AIR injection pumps and a little black box that only controlled the associated diverter valves. Oh, yeah and they did have an EFE valve.

The manifolds were beautiful - made of shaped/welded stainless steel - as were the mufflers & pipes. These manifolds are 30 years old:

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Here is one of the two mufflers I recently bought for my restoration project. My originals were just looking kind of ratty - but were still fully intact

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They were hard to find and cost me big money. If you are interested, they are out there however they go for about about $300:

https://www.ebay.com/p/NOS-OEM-GM-Muffler-Exhaust-15529620/670121564?iid=131996466797&chn=ps

Everything from the cylinder heads to the tips of the tail pipes was made of high quality stainless steel. I had to trim the exhaust pipes a bit to fit the new mufflers - and in the process, I went through about 5 of those Torch sawzall blades.

This is what your exhaust system looked like originally:

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You can probably source a set of manifolds and mufflers easy enough, but the exhaust/tail pipes will be more of a challenge. But the good news is, if you can find a set of pipes in a JY or C/L, they will almost certainly be like new.

1987chevybad · Jan 19, 2019

There's no air pumps on mine. They were never there or removed. My truck is a C&C truck and the GVWR is 12500.

Those look nice, why the hell would someone throw crappy headers on.

chengny · Jan 19, 2019

1987chevybad said:
There's no air pumps on mine. They were never there or removed. My truck is a C&C truck and the GVWR is 12500.

Those look nice, why the hell would someone throw crappy headers on.

My 30 has a GVWR of - I think 10500 - and it came with them. Ah who knows?

Yeah I love those manifolds too.

75gmck25 · Jan 20, 2019

These tubular manifolds are still available from Rock Auto, but they are about $175/manifold ($350 a set). However, if they flow better, it might be worth it because they wouldn't rust out as fast as headers. https://www.rockauto.com/en/moreinfo.php?pk=971500&cc=1053098&jsn=10603&jsn=10603

Do they have flanges for 2 1/2" exhaust pipes?

Did they do anything special to fit factory 2 1/2" pipes on those '86 K30's? There isn't much space for the 2" duals on my '75, and 2 1/2" pipes would have very little clearance around the transfer case.

Bruce

1987chevybad · Jan 20, 2019

75gmck25 said:
These tubular manifolds are still available from Rock Auto, but they are about $175/manifold ($350 a set). However, if they flow better, it might be worth it because they wouldn't rust out as fast as headers. https://www.rockauto.com/en/moreinfo.php?pk=971500&cc=1053098&jsn=10603&jsn=10603

Do they have flanges for 2 1/2" exhaust pipes?

Did they do anything special to fit factory 2 1/2" pipes on those '86 K30's? There isn't much space for the 2" duals on my '75, and 2 1/2" pipes would have very little clearance around the transfer case.

Bruce

Ya the transmission crossmemebers are different for single/dual exhaust.

There Vin tag on my door is long gone, someone could have retagged it long ago.

I think I might buy manifolds and a y pipe spec'D for a K10, I don't need or want to pay for a dual setup.

WFO · Jan 20, 2019

chengny said:
85 & 86 K30's (as well as K20's with the HD5/FED emissions package) got really nice exhaust systems. I'm on my third 86 - two were 20's and my current is a 30 - and they all have had dual 2 1/2" pipes. They were all over a certain GVRW (8500 lb. IIRC) and so they were essentially free of most emissions controls. No cats, no O2 sensors, etc. They had two AIR injection pumps and a little black box that only controlled the associated diverter valves. Oh, yeah and they did have an EFE valve.

The manifolds were beautiful - made of shaped/welded stainless steel - as were the mufflers & pipes. These manifolds are 30 years old:

You must be registered for see images attach

[

chengny, I have an 86 K20 with the C6P option, that has those stainless manifolds. All the AIR stuff was long gone when I got the truck.
Can those 8 AIR tubes be removed from the manifolds, and plugged? They look to be restrictive if not hooked up to a pump. If so, would you happen to know what size plugs they take?

chengny · Jan 20, 2019

WFO said:
chengny, I have an 86 K20 with the C6P option, that has those stainless manifolds. All the AIR stuff was long gone when I got the truck.
Can those 8 AIR tubes be removed from the manifolds, and plugged? They look to be restrictive if not hooked up to a pump. If so, would you happen to know what size plugs they take?

Good question. The diameter and thread pitch of the bosses in the manifold (and the tube fittings that go in them) is a closely guarded secret. I say that only partially in jest. I once read that the GM engineers purposely spec'd an extremely obscure thread style to discourage the end users from defeating the system.

Don't quote me, but I have heard that a #10 flare fitting (from a hydraulic supply house) is as close to the correct size as you'll get. They are fine thread, not tapered and flared to seat in the manifold.

There are any number of solutions to seal those holes, but I always keep mine factory - and remove the electric portion of the diverter valve control system. I do retain the high vacuum signal from carburetor/manifold - to minimize backfiring on decel. I don't have any proof, but it seems that running the blowers extends the life of the entire exhaust system.

WFO · Jan 21, 2019

Thanks chengny.
I'll try those flare fittings if I ever need to pull the manifolds, or get a new exhaust.
I think your probably right about extending the life. Mine has the original exhaust back to the mufflers. Someone else put glass packs and different tail pipes on it.

1987chevybad · Jan 21, 2019

My dad said the air injection used to blow the mufflers off cars often.

Rusty Nail · Jan 21, 2019

chengny said:
85 & 86 K30's (as well as K20's with the HD5/FED emissions package) got really nice exhaust systems. I'm on my third 86 - two were 20's and my current is a 30 - and they all have had dual 2 1/2" pipes. They were all over a certain GVRW (8500 lb. IIRC) and so they were essentially free of most emissions controls. No cats, no O2 sensors, etc. They had two AIR injection pumps and a little black box that only controlled the associated diverter valves. Oh, yeah and they did have an EFE valve.

The manifolds were beautiful - made of shaped/welded stainless steel - as were the mufflers & pipes. These manifolds are 30 years old:

You must be registered for see images attach

You must be registered for see images attach

Here is one of the two mufflers I recently bought for my restoration project. My originals were just looking kind of ratty - but were still fully intact

You must be registered for see images attach

They were hard to find and cost me big money. If you are interested, they are out there however they go for about about $300:

https://www.ebay.com/p/NOS-OEM-GM-Muffler-Exhaust-15529620/670121564?iid=131996466797&chn=ps

Everything from the cylinder heads to the tips of the tail pipes was made of high quality stainless steel. I had to trim the exhaust pipes a bit to fit the new mufflers - and in the process, I went through about 5 of those Torch sawzall blades.

This is what your exhaust system looked like originally:

You must be registered for see images attach

You can probably source a set of manifolds and mufflers easy enough, but the exhaust/tail pipes will be more of a challenge. But the good news is, if you can find a set of pipes in a JY or C/L, they will almost certainly be like new.

Omg it's beautiful!

*feen*

1987chevybad · Jan 22, 2019

Well it looks like headers are cheaper and I can't find used manifolds and there's no way in hell I'm pulling those off Ina junkyard.

I think I'm going to do headers, a short pipe and regular old turbo mufflers or flowmaster 40s.

What's the best setup for headers? Obviously natural ones will rot out almost instantly, but ceramic vs stainless?

What do you think?

Need a new exhaust

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