Ever design exhaust for towing?

I want to redo the exhaust on my truck from the hacked duals. I was thinking 2.5 y pipe to 3" cat back to 2.5" dual straight through mufflers then tail pipes. Any input on how this would perform on my 350 and later on a 454?

I would go 3 and a quarter and remove the cats but keep the exhaust for some more air flow gives you a little more power also like the idea of the y pipes I wanna see more info on what u do also if u could possibly dyno it? Before and after maybe

I have heard a bigger pipe for torque.
If it were Mine, I would not go smaller than a 3", especially of later going to a 454.

MrMarty51 said:

I have heard a bigger pipe for torque.
If it were Mine, I would not go smaller than a 3", especially of later going to a 454.

Click to expand...

So it might not be clear what i meant 2.5" pipes from manifolds/headers to adapter like this
then 3 in cat and pipe for a few feet to another adapter like above. Then 2.5 to mufflers and tail pipe. Like the factory systems on the 88-93 trucks did.

The other options is stay 2.5 but route both down the ds and use and xpipe in place of the cat to help with scavenging.

Either way the theory behind my idea is exhaust gases are expanded and create velocity leaving the block this pushes through the 2.5 adequately. By the time it reaches the 3" it has cooled and contracted enough to lose some velocity, add in the second bank and now its twice the cooled exhaust in the 3" to pick the velocity back up as it goes through the cat/x pipe then it would be straight pipe to the mufflers.


And this supports the info with a 350 and 300 hp, when the 454 goes in it might be 400 hp, I dont know of a source of info like this for torque.
http://www.hotrod.com/articles/what-exhaust-pipes-work-best/

Real8deal said:

I would go 3 and a quarter and remove the cats but keep the exhaust for some more air flow gives you a little more power also like the idea of the y pipes I wanna see more info on what u do also if u could possibly dyno it? Before and after maybe

Click to expand...

Its an auto so the dyno probably wont event start till 3k and be totally useless for area I am trying to improve

I'm going to jump right here. First, bigger is less torque. You loose all low end and gain high end hp, its not worth going too big.

If I understand:
2.5 from header, to 3 inch y pipe, 3 inch cat, two 2.5 inch muffler to tail pipes

My question is why y-pipe?

With these sizes, you dont have to worry about scavenging. There have been many dyno tests that show putting an x-pipe, h-pipe, and removing/replacing cats, do not really impact anything.

spanky55amg said:

I'm going to jump right here. First, bigger is less torque. You loose all low end and gain high end hp, its not worth going too big.

If I understand:
2.5 from header, to 3 inch y pipe, 3 inch cat, two 2.5 inch muffler to tail pipes

My question is why y-pipe?

With these sizes, you dont have to worry about scavenging. There have been many dyno tests that show putting an x-pipe, h-pipe, and removing/replacing cats, do not really impact anything.

Click to expand...

2.5 from headers to the the pictured adapter that would be 3in out to cat, 3" from cat for couple of feet to another adapter back to 2.5. So it would be using the smaller pipes where not merged.

Y pipe because I only wan to buy 1 cat, have always heard the merge at the y pipe close helps with low end torque.

Bigger inches create torque just not in the exhaust....

Do you have to have cats to get it inspected?

To save some more money, use 3" pipe from the cat into a 3" muffler that has dual 2.5" outs. I used to do this with my 94 and 95 Surburbans.

gpmorgan said:

Do you have to have cats to get it inspected?

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No but dont want to mess with it if I move somewhere that inspects.

Craig 85 said:

To save some more money, use 3" pipe from the cat into a 3" muffler that has dual 2.5" outs. I used to do this with my 94 and 95 Surburbans.

Click to expand...

Already have the 2.5 mufflers, still feel the same?

4WDKC said:

No but dont want to mess with it if I move somewhere that inspects.

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I know, that if you move into a state that inspects, the cats must be in the factory location. And I think the only state that still inspects our old ass trucks is California. Ever other state that I know of has a limit on how far back they inspect for smog. I could be super wrong, this is only to MY knowledge.

that said.
The y-pipe from my knowledge doesnt help with torque at all. If youre doing it to buy one catalyst for your own reason, then just go for it. But from an exhaust-to-power reason, doing this exhaust work will accomplish nothing.

• catalyst do not affect hp or tq
• if you stay within 2.5-3 inches (on our trucks in a stock-ish power plant) will not change much
• y-pipe, h-pipe, x-pipe, no cross over - it doesnt matter much accept for sound... and it will change the sound.
• you dont need to worry about back pressure or scavenging.

These things all take in theory. But in real world applications, they do not change things (very much.) Now what would change things are long tub headers vs stock manifolds or shorties. 2 inch exhaust vs 2.5 or 3 inch. And if you are going to y-pipe, the 3 inches should be good up to something like... 450 or 500 hp. Those numbers come from LS1 F-bodies.

Edit to include:
Torque is built by cubic inches, cam profile, intake, headers, and torque converter if your an automatic guy.

To confuse the issue further, read:
https://www.castheads.com/manifolds-carb/exhaust-manifolds/2-into-1-exhaust-collector-systems/

Now, to answer the question directly, yes, i think both the 350 and 454 will be fine with the 2.5 into Y, then 3 cat, then split back into two 2.5 pipes. i don't know much about exhaust, so take that with a grain of salt. But my feeling is that this system will be ok with both engines.......

2) On a side note, i have never built a towing engine, so also take the following with a grain of salt:

First, i think i would be looking at 350 minimum, but preferably 383. Specifically the 383HT. With gas this cheap, and expected to stay that way for a good long while, i think this is feasible. (Although my ideal towing engine would be a 6.2 diesel with banks turbo kit)

Secondly, and possibly more importantly, i'm not sure if i would want to run headers on a towing engine---or for that matter anything that is driven on the street for various reasons----possibly run too hot, do they seal correctly, durability etc.

Instead, i would be looking at the later (as in 87 and up) factory exhaust manifolds for the small block, which kinda resemble tube headers but aren't really headers.

Since i want things cheap, simple and easy, i would just run two pipes and mufflers from both manifolds and have dual exhaust, even though 2 into 1 may be better.

Keep the mechanical clutch fan and shroud.

So what are you planning for y-pipe

4WDKC said:

So it might not be clear what i meant 2.5" pipes from manifolds/headers to adapter like this

You must be registered for see images attach

then 3 in cat and pipe for a few feet to another adapter like above. Then 2.5 to mufflers and tail pipe. Like the factory systems on the 88-93 trucks did.

The other options is stay 2.5 but route both down the ds and use and xpipe in place of the cat to help with scavenging.

Either way the theory behind my idea is exhaust gases are expanded and create velocity leaving the block this pushes through the 2.5 adequately. By the time it reaches the 3" it has cooled and contracted enough to lose some velocity, add in the second bank and now its twice the cooled exhaust in the 3" to pick the velocity back up as it goes through the cat/x pipe then it would be straight pipe to the mufflers.


And this supports the info with a 350 and 300 hp, when the 454 goes in it might be 400 hp, I dont know of a source of info like this for torque.
http://www.hotrod.com/articles/what-exhaust-pipes-work-best/

Click to expand...

What are your plans for headers or manifolds and then what are the plans to get the header pipes to the adapter pictured above? I'm sticking with manifolds, just not sure if I'm going to use TBI, Vortec or Ramshorns. The latter two options will for sure need custom y-pipe (i'm going single 3" all the way back after the y) but even if I stick with OEM TBI manifolds I still want to get a better flowing y-pipe. Unfortunately, the Walker Y-pipe for our trucks seems to have been discontinued. And vortec y-pipe wouldn't work since single pipe is on passenger side.

I bought my '91 in 2014 - WA has a rolling 25 year limit on emissions so I had to get it tested only when I first bought it and now I'm done. PO lived in a rural area where there was no testing req'd and he removed the cat. When I brought it in for testing I fully expected it to fail, but amazingly it passed no problem. They didn't even look under it to see if it was there, tail pipe sniff only. That all being said, I'm thinking about adding it back in just because the exhaust stinks so much. I have a 3" aftermarket cat from my parts rig that looks to be in decent shape. I really don't think a cat would have much effect on a low rpm torque motor.

To confuse the issue further, read:
https://www.castheads.com/manifolds-carb/exhaust-manifolds/2-into-1-exhaust-collector-systems/

Now, to answer the question directly, yes, i think both the 350 and 454 will be fine with the 2.5 into Y, then 3 cat, then split back into two 2.5 pipes. i don't know much about exhaust, so take that with a grain of salt. But my feeling is that this system will be ok with both engines.......

2) On a side note, i have never built a towing engine, so also take the following with a grain of salt:

First, i think i would be looking at 350 minimum, but preferably 383. Specifically the 383HT. With gas this cheap, and expected to stay that way for a good long while, i think this is feasible. (Although my ideal towing engine would be a 6.2 diesel with banks turbo kit)

Secondly, and possibly more importantly, i'm not sure if i would want to run headers on a towing engine---or for that matter anything that is driven on the street for various reasons----possibly run too hot, do they seal correctly, durability etc.

Instead, i would be looking at the later (as in 87 and up) factory exhaust manifolds for the small block, which kinda resemble tube headers but aren't really headers.

Since i want things cheap, simple and easy, i would just run two pipes and mufflers from both manifolds and have dual exhaust, even though 2 into 1 may be better.

Keep the mechanical clutch fan and shroud.

1. The 350 is currently in the truck and will only be removed when the 700r4 quits. I already have a 96 Vortec 454 ecm,harness, manifolds and headers, 208 case from a th400 and a 2wd 4l80e waiting in the garage. So why rebuild the 350 to a 383 and hassle with finding an od transmission to work behind it.
2. Routing the PS exhaust is a pita to get around the t case and while true duals frees up power over a poorly designed stock exhaust system. The theory (as I understand it) is it loses low end to free up high end over a properly designed stock system.

Daveo91Burb said:

So what are you planning for y-pipe


What are your plans for headers or manifolds and then what are the plans to get the header pipes to the adapter pictured above? I'm sticking with manifolds, just not sure if I'm going to use TBI, Vortec or Ramshorns. The latter two options will for sure need custom y-pipe (i'm going single 3" all the way back after the y) but even if I stick with OEM TBI manifolds I still want to get a better flowing y-pipe. Unfortunately, the Walker Y-pipe for our trucks seems to have been discontinued. And vortec y-pipe wouldn't work since single pipe is on passenger side.

I bought my '91 in 2014 - WA has a rolling 25 year limit on emissions so I had to get it tested only when I first bought it and now I'm done. PO lived in a rural area where there was no testing req'd and he removed the cat. When I brought it in for testing I fully expected it to fail, but amazingly it passed no problem. They didn't even look under it to see if it was there, tail pipe sniff only. That all being said, I'm thinking about adding it back in just because the exhaust stinks so much. I have a 3" aftermarket cat from my parts rig that looks to be in decent shape. I really don't think a cat would have much effect on a low rpm torque motor.

Click to expand...

The factory Y pipes for our trucks and the GMT400 were terrible from the beginning a stock replacement was not even considered. I don't have a definitive answer for the manifolds/header questions as I have the stock 87 manifolds I will consider these my last resort. I have a set of 2nd gen fbody long tubes that were give to me to see if the fit, not sure how it will with the tcase. The other option is XS power shorties for a 88-95 truck I bought, obviously the ypipe is dependent on which exhaust gets used. I want to route the PS to the DS and finish the exhaust on the DS similar stock system exit.