My tailpipe is the size of a cocktail straw

[L31MaxExpress]

This is what I was talking about, mating larger pipe to the manifold flange. This was factory GM to mate the 2.25" manifold outlets to dual 3" pipes on my 97 Express.

You must be registered for see images attach

It is hard to see, but Doug Thorley did the same to mate there 3" head pipes to their 2.5" collectors.

You must be registered for see images attach

 

[Erik the Awful]

I've never had headers so I'm just basing that on assumptions and could potentially be convinced otherwise, but I'm not trying to get into expensive ceramic coatings and the like

Ceramic coatings are great for keeping headers looking nice, but they do nearly nothing for heat management. Header wrap is very effective for heat management, but it's not suitable for a street vehicle because it traps moisture and rusts the headers out. For a street van, a heat barrier on the firewall and doghouse is better.

Summit Racing SUM-350301 Summit Racing™ Heat Shields | Summit Racing

Free Shipping - Summit Racing™ Heat Shields with qualifying orders of $109. Shop Heat Barrier and Sound Deadening Mats at Summit Racing.

www.summitracing.com

 

[Hipster]

If it were my van, absolutely #1. But it's your van, so absolutely #2 and take pictures.

and his money. LOL

I ordered a 3 inch passenger side tail pipe(stock diesel but it's a P/U) and a 3 inch in/out muffler for mine off a 3 inch Cat that's already there. Good enough for me .....for now.

 

[BVRPLZR]

Cheapest option would be keep whatever manifolds you have, keep the flange and 2" of pipe after the flange, weld 2.5" pipes over those that are bent to mate to a 2.5 to 3" merge Y, then a 3" high flow cat, single 3" pipe, 3" muffler of your choice and a 92-95 350 G20 3" tail pipe. Personally I would swap to headers or the Hooker manifolds. Summit actually sells a header/dual exhaust kit but they do not come with cats.

This seems like the way to go. I've been eyeing the Hooker manifolds for a while, as well as that header/dual exhaust kit, but this is a total pleasure cruiser not a hot rod so I'm trying to practice restraint and forget about the dual exhaust kit.

I've been doing a lot of reading but I still don't really understand this concept: if the manifold outlets are only 2.25" or 2.5", why would you want anything downstream to be bigger than that?
I understand that the extra volume would allow the gasses to expand and slow down, but I guess I don't understand why you would want or not want that, or where in the exhaust chain you would want to modulate diameter.
Is the overall system not limited by its smallest diameter point?


Also, thanks for all the replies. I'll try and snap some pics next time I can get under the ole girl.

I will probably go ahead and replace the heat barrier on the doghouse when I do this, regardless of what I end up doing with the exhaust.

 

[L31MaxExpress]

This seems like the way to go. I've been eyeing the Hooker manifolds for a while, as well as that header/dual exhaust kit, but this is a total pleasure cruiser not a hot rod so I'm trying to practice restraint and forget about the dual exhaust kit.

I've been doing a lot of reading but I still don't really understand this concept: if the manifold outlets are only 2.25" or 2.5", why would you want anything downstream to be bigger than that?
I understand that the extra volume would allow the gasses to expand and slow down, but I guess I don't understand why you would want or not want that, or where in the exhaust chain you would want to modulate diameter.
Is the overall system not limited by its smallest diameter point?


Also, thanks for all the replies. I'll try and snap some pics next time I can get under the ole girl.

I will probably go ahead and replace the heat barrier on the doghouse when I do this, regardless of what I end up doing with the exhaust.

2.5" happens to be a good size for a 350 especially merged into a single 3" pipe. I have run the dual 2.5" to single 3" on multiple small blocks and it works well. A small 2" pipe is more restrictive than a 2.25 or 2.5" pipe even with the same 2" manifold flanges. Something I learned in physics class years ago. Take an ordinary drinking straw, blow into it. It will have loads of backpressure. Now take the same straw, cut a short piece off it. Now blow into it. Air will move much easier through the same sized opening. When the exhaust valve opens, the exhaust pressure wave is under substantial pressure. That wave cools and weakens as the exhaust travels down the pipe toward the muffler and ultimately the tailpipe. In the scenario I mentioned you want want to leave enough of a pipe stub to weld the 2.5" pipe to and be able to remove the flange if the need arises. For some OEM applications, I have seen GM run a ~2.25" pipe from the manifold to the cats and step up to dual 2.75" after the cats. GM did that to help minimize the warmup time for the catalysts while minimizing exhaust restriction. The 6.2L GenIV LS engines are like that. Dual cats right off the manifold, larger streamlined pipes after the cats to a very nice Y and a single 3.5" exhaust after the Y.

 

[BVRPLZR]

You must be registered for see images attach

Might have to CSI zoom and enhance, but I assure you there's a tailpipe in this photo.

 

[RichLo]

Awweee ... thatssss ... soooo ... cuuuuute!!!

 

[tayto]

2.5" happens to be a good size for a 350 especially merged into a single 3" pipe. I have run the dual 2.5" to single 3" on multiple small blocks and it works well. A small 2" pipe is more restrictive than a 2.25 or 2.5" pipe even with the same 2" manifold flanges. Something I learned in physics class years ago. Take an ordinary drinking straw, blow into it. It will have loads of backpressure. Now take the same straw, cut a short piece off it. Now blow into it. Air will move much easier through the same sized opening. When the exhaust valve opens, the exhaust pressure wave is under substantial pressure. That wave cools and weakens as the exhaust travels down the pipe toward the muffler and ultimately the tailpipe. In the scenario I mentioned you want want to leave enough of a pipe stub to weld the 2.5" pipe to and be able to remove the flange if the need arises. For some OEM applications, I have seen GM run a ~2.25" pipe from the manifold to the cats and step up to dual 2.75" after the cats. GM did that to help minimize the warmup time for the catalysts while minimizing exhaust restriction. The 6.2L GenIV LS engines are like that. Dual cats right off the manifold, larger streamlined pipes after the cats to a very nice Y and a single 3.5" exhaust after the Y.

I haven't run the Holley cast manifolds myself,but this is the route I would go. I'm done with headers, i went with stock cast iron manifolds on my squarebody. factory wires and looms work,no leaks,no excessive heat. i will probably upgrade to the Holley ones eventually as i got dorman manifolds and they are pretty crappy even after a few hours with the die grinder..

 

[BVRPLZR]

Awweee ... thatssss ... soooo ... cuuuuute!!!

My girlfriend says it's perfect