Stock manifolds to 3” exhaust

[DusterDaddy415]

I’m thinking of ditching the long tube headers on ‘72 Duster. They’re just in the way of things and the excess heat is causing issues.
My question is has anyone mated a stock manifold to 3” exhaust? That’s what is in my car currently with my long tubes with 3” collectors. Thanks.

 

[RustyRatRod]

WHICH manifolds?

 

[318willrun]

I used the 2.5" TTI headpipes on manifolds. You could use them and run into your existing 3"

 

[DusterDaddy415]

I used the 2.5" TTI headpipes on manifolds. You could use them and run into your existing 3"

Nice. So they are direct fit from stock manifolds to 3” exhaust? Looking for simplicity.

 

[318willrun]

Nice. So they are direct fit from stock manifolds to 3” exhaust? Looking for simplicity.

here are the manifolds i used on both my Dusters (bought 2 sets).

 

[Mike69cuda]

I didn’t like the sound of 3 inch exhaust on my barracuda. The pipes were too big to go over the rear axles without issues. Just my opinion.

 

[318willrun]

I didn’t like the sound of 3 inch exhaust on my barracuda. The pipes were too big to go over the rear axles without issues. Just my opinion.

even 2.5" is tight going around the axle

 

[fishmens67]

Nice. So they are direct fit from stock manifolds to 3” exhaust? Looking for simplicity.

A 3'' pipe won't seal on an exhaust manifold, 2.5" max.
If you're ditching the headers, a full 2.5" exhaust would be best.

even 2.5" is tight going around the axle

I have 3'' off the headers into hooker mufflers with 2.5 tail pipe, it is very tight in the axle area, shocks, electric fuel pump..... you get the drift.

 

[Ottmundr]

even 2.5" is tight going around the axle

That's why they invented the AAR. ;)

 

[mbaird]

We are lucky to have a good exhaust shop still . I took them a Summit 3” kit for my 69 Swinger and they modified/installed it for what I consider really cheap ! And it fits fabulously ! I think it ran $300 labor back in 2019 . I was so impressed that I brought my 68 Barracuda back to them .
Did a great job on it as well .

Both cars run all the way back and thru stock style tips .

 

[Ottmundr]

We are lucky to have a good exhaust shop still . I took them a Summit 3” kit for my 69 Swinger and they modified/installed it for what I consider really cheap ! And it fits fabulously ! I think it ran $300 labor back in 2019 . I was so impressed that I brought my 68 Barracuda back to them .
Did a great job on it as well .

Both cars run all the way back and thru stock style tips .

Well, where's the car ****?

 

[318willrun]

A 3'' pipe won't seal on an exhaust manifold, 2.5" max.
If you're ditching the headers, a full 2.5" exhaust would be best.

I have 3'' off the headers into hooker mufflers with 2.5 tail pipe, it is very tight in the axle area, shocks, electric fuel pump..... you get the drift.

2.5" will flow a lot of small block. Actually, a lot of big block as well.

 

[mbaird]

I know I took detailed pictures but can’t find them now. Any body else have pictures disappearing from their phone ?
I have hundreds of blank white squares where pics used to be in my library ?

 

[fishmens67]

2.5" will flow a lot of small block. Actually, a lot of big block as well.

It flows enough, besides I have cutouts. lol

 

[RustyRatRod]

You can in all likelihood get 3" pipes on the manifolds on the 68-71 manifolds. They have a flat flange face instead of a ball flange. 2.5" pipes fit easily and there is a lot of room between the outlets and the exhaust studs. A GOOD exhaust shop could do it. No telling what it'd cost.

 

[Professor Fate]

If you've got enough motor to warrant a 3" exhaust, I think you're gonna be disappointed with most any exhaust manifold.
BUT- of course it can be done.
Get the best manifolds you can, The '68-'71 340 manifolds are about the best you can get, followed by the '71-'73 340 manifolds.
I'd find a good exhaust shop to fab the headpipes, 3" if there's room, 2 1/2 if there's not- but be forewarned, most places have a difficult time making the extreme bend required for the driver's side manifold; so 3" and maybe even 2 1/2 may be a no-go.
An alternative is to get your pipes from Tti, although I think you're limited to 2 1/2 from them.
If you go 2 1/2, this would be the time to have the shop fab up an H pipe section, which would also act as a transition from the headpipes to the 3" exhaust.
JMO.

 

[RustyRatRod]

If you've got enough motor to warrant a 3" exhaust, I think you're gonna be disappointed with most any exhaust manifold.
BUT- of course it can be done.
Get the best manifolds you can, The '68-'71 340 manifolds are about the best you can get, followed by the '71-'73 340 manifolds.
I'd find a good exhaust shop to fab the headpipes, 3" if there's room, 2 1/2 if there's not- but be forewarned, most places have a difficult time making the extreme bend required for the driver's side manifold; so 3" and maybe even 2 1/2 may be a no-go.
An alternative is to get your pipes from Tti, although I think you're limited to 2 1/2 from them.
If you go 2 1/2, this would be the time to have the shop fab up an H pipe section, which would also act as a transition from the headpipes to the 3" exhaust.
JMO.

I cannot disagree with any of that. Also, I'll add this. I don't know what it is.....alien technology, radioactive butterflies, little slutty fairies, but when going from 2.5" to 3" it makes a drastic noise difference. Like a ground shakin noise. So like and some don't.

 

[1WildRT]

TTI Sells headpipes for 3" exhaust to manifolds... But not for A bodies....

 

[4mulas]

Dual 3" exhaust is likely overkill. If you have headers now and are just trying to salvage the exhaust from the collector onward why not just step it down into a Size that is manageable under the car and run 2.25 or 2.5" from the collector forward..

 

[33IMP]

If you HAVE manifolds, all you need is a 2 1/2 headpipes to take the place of the headers, and then they can be hooked to existing pipes. You could even use a reducer on the new headpipe to mate with existing header flange on the pipes you have.
Cheapest easiest route.
I'd try to find a local muffler shop that can do it.

 

[DusterDaddy415]

Dual 3" exhaust is likely overkill. If you have headers now and are just trying to salvage the exhaust from the collector onward why not just step it down into a Size that is manageable under the car and run 2.25 or 2.5" from the collector forward..

Yeah I think I’m going to look into downsizing to 2.5in exhaust. The car is loud as hell. It sounds good tho. I must be getting old

 

[DusterDaddy415]

If you've got enough motor to warrant a 3" exhaust, I think you're gonna be disappointed with most any exhaust manifold.
BUT- of course it can be done.
Get the best manifolds you can, The '68-'71 340 manifolds are about the best you can get, followed by the '71-'73 340 manifolds.
I'd find a good exhaust shop to fab the headpipes, 3" if there's room, 2 1/2 if there's not- but be forewarned, most places have a difficult time making the extreme bend required for the driver's side manifold; so 3" and maybe even 2 1/2 may be a no-go.
An alternative is to get your pipes from Tti, although I think you're limited to 2 1/2 from them.
If you go 2 1/2, this would be the time to have the shop fab up an H pipe section, which would also act as a transition from the headpipes to the 3" exhaust.
JMO.

I have been looking at TTI. They are nice but expensive.

 

[33IMP]

3" isn't automatically loud. It depends on the mufflers you have, and whether you have tailpipes or dumps.
In your situation (bye bye headers, and quieter please) I'd have some headpipes made off your manifolds (if you have some) and a pair of longest triple pass 3" (turbo style) that will fit under the car.
Should solve both problems.
If you decide to change the whole system, I'd look at jegs and summit house brand systems.

 

[Kern Dog]

WHICH manifolds?

Why would it matter? Tests on a 300 HP 360 showed only 7 HP difference between 273/318 manifolds and the "famous" 340 units.

If you've got enough motor to warrant a 3" exhaust, I think you're gonna be disappointed with most any exhaust manifold.

I agree here.

Get the best manifolds you can, The '68-'71 340 manifolds are about the best you can get, followed by the '71-'73 340 manifolds.

The money spent on 340 manifolds would buy another set of headers.
What is the issue of heat? Iron manifolds retain more heat than thin steel tubes do.

 

[RustyRatRod]

Why would it matter? Tests on a 300 HP 360 showed only 7 HP difference between 273/318 manifolds and the "famous" 340 units.



I agree here.



The money spent on 340 manifolds would buy another set of headers.
What is the issue of heat? Iron manifolds retain more heat than thin steel tubes do.

It matters because a 3" pipe can be made to fit the 68-71 manifolds. I mentioned nothing about power. Only fitment. While 3" pipes can be made to fit the flat HP flanges, I believe the bigger challenge would be getting 3" pipes around the torsion bars. The OP didn't ask about power production and I was not addressing that. He asked if 3" pipes will FIT on manifolds. They will if they are the right ones.