Exhaust manifold outlet diameter?

[timk225]

I'm thinking of making an improved exhaust for my 1973 Duster, but just sticking with the stock exhaust manifold. I had gotten an exhaust flange and the first couple feet of pipe from a Super Six car, but was surprised to see the pipe diameter was smaller than the 2-1/4" I'd read it was. I was thinking of getting a mandrel bent piece of pipe and fitting it to the factory flange to start a new exhaust pipe off at the correct size.

If anyone has an exhaust manifold laying around, what's the diameter of the outlet, and the spacing, center to center, of the 2 mounting bolts?

 

[MidnightSwinger]

Here you go, stock super six exhaust manifold. I have noticed some improvement by port matching the exhaust runners and opening the exhaust flange up to 2 1/4. Previously I had a machinist friend doing it, but since he has passed away, I’m probably gonna try doing it with grinder.

 

[Rug_Trucker]

I tried opening with up with the carbides I use to port heads. They didn't work at all!

 

[Hyper_pak]

I tried opening with up with the carbides I use to port heads. They didn't work at all!

Use the softer grinder type bits, they give up pretty fast but will eat the cast iron.

I have a Dart Lite, when I drop the exhaust system, I will try and remember to post what size the pipe is.

 

[halfafish]

All my stock exhaust outlets have been just a little under 2". The head pipes have been either 1-7/8" or one Super Six that was 2". @RustyRatRod hogged out his manifold nicely, perhaps he will repost his photosand info.

 

[timk225]

Thanks for the good detailed photos!

 

[RustyRatRod]

All my stock exhaust outlets have been just a little under 2". The head pipes have been either 1-7/8" or one Super Six that was 2". @RustyRatRod hogged out his manifold nicely, perhaps he will repost his photosand info.

Sure. Here's what a friend did for me. I must admit too, it made a very noticeable difference, but my engine is far from stock. I could tell a difference on the stock 170 too, though, because I used bigger pipe with it. The key is to use at least the same diameter head pipe AT the manifold outlet as well as all the way back, or there's really no need to do it. He's taken a second manifold out to 2.5" and there was still meat leaf. I'm 100% certain they will go to 3", but they would be pretty thin. As long as you were careful putting them on though, you'd probably be ok. lol But the 2.5" is plenty strong.

Exhaust Manifold Mod

Don't know how many of yall are interested, but here's what I did. Well.......here's what my friend Freddie did. LOL Since I am a walking retard with a grinder, I asked my friend Freddie about enlarging a slant manifold outlet. He took it out to 2 1/4" with meat left over. He said he was sure...

www.forabodiesonly.com

 

[slantsixdan]

I'm thinking of making an improved exhaust for my 1973 Duster

Good recipe: 2¼" headpipe into this muffler. It's in Walker's QuietFlow SS premium OE line, all stainless steel (which is nice for durability), made for the '01 Jeep Cherokee 4.0 so it's easily got the flow capacity for a healthy 225 and it's tuned to keep an inline-6's exhaust from droning, has a 2¼" inlet and outlet. The inlet has a 2-bolt flange meant to bolt directly to the outlet of the Jeep's catalytic converter, and if you want to put the system together for E-Z muffler replacement you can put a mating flange on your headpipe, or there's plenty of length to the muffler's input pipe that the flange can just be sawed off in 5 seconds at the exhaust shop. It's got the 4¼" × 9¾" housing, muffler shell 20" long, so it'll be a bit of a tight fit in an A-body, but it will fit.

2" tailpipe with resonator (2¼" is not better, just louder). If I'm rich, I like a Flowmaster HP2 stainless unit with 2" in and out. It's 18" long, which is a workable fit behind an A-body quarter panel. If I'm broke, I like a Walker № 17198 4" round can-type unit, 2" in and 2" out, with offset outlet next to a proper hanger bracket.

Speaking of that, whatever muffler you wind up with, make sure to use very soft hangers. The hook-and-O-ring type, for example. Today's popular "rod and rubber box" type transmits a lot of noise to the passenger compartment.

(Tailspout outlet 45° or greater downward.)

I was thinking of getting a mandrel bent piece of pipe and fitting it to the factory flange

Use a new flange at the top of your new headpipe—the old ones like to warp after half a century's thermal cycling.

to start a new exhaust pipe off at the correct size.

Can ream out the nominally-2" manifold outlet a bit, but don't get carried away.

All the Slant-6 cars were supposed to get 2¼" headpipes for '77:

At least some of them probably didn't; Chrysler were bleeding out and circling the drain at the time, quality control was already down the toilet, and every last fraction of a cent counted. Plus, who knows how many exhaust pipes have been replaced over the decades, with whatever came to hand/was on the shelf/etc.

 

[timk225]

How about that heat flapper valve in the exhaust manifold? Mine turns freely, at least when the engine is cold. Is it worth the trouble to cut it out at least partly?

I replaced the old muffler last autumn with another 2" in and out muffler, I think it was a Walker super turbo, it is pretty quiet. I will use the rubber loop hanger brackets, I hate droning exhaust. Anyone got a part number for a replacement exhaust manifold flange? I need to figure out what angles of mandrel bent pipes to get, I don't want some muffler shop using compression bent pipes in the system. One angled piece for right off the manifold and another for down by the transmission shift linkage, to start going straight back under the floor.

 

[volaredon]

All my stock exhaust outlets have been just a little under 2". The head pipes have been either 1-7/8" or one Super Six that was 2". @RustyRatRod hogged out his manifold nicely, perhaps he will repost his photosand info.

As I did too. Mine started at 1-7/8 and is now gasket matched to 2-1/4. That 1-7/8 wasn't centered very well within the 2-1/4" hole in the gasket with the gasket hanging on the studs
And the carbides I have ate right thru the manifold material like it was "nothing"

 

[timk225]

I recently got an iron Super Six 2 bbl intake manifold, from a junkyard in Kansas City, and along with the air cleaner and brackets, I had them cut the exhaust pipe about a foot and a half from the manifold flange and send that too. I would have preferred an aluminum intake but iron was all I could find and it was 21.4 pounds on my scale. I just measured the exhaust pipe, and it was 1-7/8" outside diameter and a very sad 1-5/8" inside diameter!

I've considered putting on headers or some other sort of improved exhaust, but for all the more I intend to build up the Slant 6, I think a ported stock manifold will probably be fine. But I do want to put on a 2-1/4" exhaust. Maybe even 2-1/2" back to the muffler.

Or would a 2-1/2" pipe be going too big and hurting more than helping? I think a local mechanic and I can piece together a full mandrel bent 2-1/4" system, I just have to look online and find the pipe pieces.

It'll be more important for this engine to have improved low end and mid range torque than all out 5000 rpm horsepower. I've got a new Holley 350 2 bbl carburetor to put on, I'll probably clean up the cylinder head ports but keep stock valve sizes. Maybe an RV-10RDP cam, not sure yet.

 

[michiganpat]

if you want cheap mandrel bends, may want to go to a U-pull-it with a calipers and a cordless sawzall. most newer cars have factory 419 stainless mandrel bent exhaust. I used sections of the tailpipe from a dodge ram (was 3") when I built the exhaust for my old 5th ave 20 years ago....my '11 charger RT has 2 1/4" exhaust, could probably grab the system and use sections (and perhaps one of the mufflers) for your slant system. quick look on facebook marketplace, there's a complete take-off stock challenger RT behind the cat exhaust near me for $100, looks almost brand new

 

[MidnightSwinger]

TTI makes a full 2 1/2 inch mandrel exhaust for your slant six duster. No welding required, just bolt it on.

 

[michiganpat]

TTI makes a full 2 1/2 inch mandrel exhaust for your slant six duster. No welding required, just bolt it on.

I've been looking at that one too....only problem is it's $485 before freight and tax charges.....if he has the ability to weld, and picking up a used take-off exhaust, he can probably build something equivalent in OEM heavy gage stainless for less $$

 

[MidnightSwinger]

I've been looking at that one too....only problem is it's $485 before freight and tax charges.....if he has the ability to weld, and picking up a used take-off exhaust, he can probably build something equivalent in OEM heavy gage stainless for less $$

I saw him enlisting a local mechanic to help, how much does that cost plus the cost of all the pieces?

 

[timk225]

I saw that exhaust article before, I reread it more closely today. I think I'll use it. I'd rather not spend the money, but by the time I get all the mandrel bent pieces, cut and fit them all together, pay the mechanic, etc, I might as well just get the kit and be done with it. In the end it'll be better. Now I have to just convince myself it is a wise use of $500 + shipping. That shouldn't be hard.

 

[RustyRatRod]

TTI makes a full 2 1/2 inch mandrel exhaust for your slant six duster. No welding required, just bolt it on.

It fits every A body. I have it on my 64 Valiant. It comes with enough pipe to fit the longer wheelbase later cars, too. It's pretty nice.

 

[michiganpat]

I saw that exhaust article before, I reread it more closely today. I think I'll use it. I'd rather not spend the money, but by the time I get all the mandrel bent pieces, cut and fit them all together, pay the mechanic, etc, I might as well just get the kit and be done with it. In the end it'll be better. Now I have to just convince myself it is a wise use of $500 + shipping. That shouldn't be hard.

hughes shows it on their website for less $$ ($411), but when I threw it in a cart, it wanted to charge me $260 for shipping....https://www.hughesengines.com/Index/products.php?browse=category&level0=SS0gU2xhbnQgNiAoMTcwLTIyNSBjLmkuIDE5NjAtMTk4Nyk=&level1=RXhoYXVzdA==&partid=34275

 

[Rug_Trucker]

$401 for a 4" turbo back Diamond Eye system for my Cummins club cab with muffler +$89 shipping........................it's heavy AF too. Great big box.

 

[slantsixdan]

How about that heat flapper valve in the exhaust manifold? Mine turns freely, at least when the engine is cold. Is it worth the trouble to cut it out at least partly?

No, it's very much worth the trouble and cost to fix it, all the way fixed, so it works all the way how it's supposed to. No matter where you live/drive; this is not a cold-weather-only thing, that'll pay you back in driveability/performance, fuel economy, oil life, and engine life. Likewise, leaving it broken will cost you on an ongoing basis in some or all of those ways. Sounds like yours is past dead, which—remember, we're talking about a half-century-old car—likely means there are other issues with the manifold. Warpage is common at both the head and pipe surfaces; so are cracks. See here.

 

[volaredon]

I have an 85 D150 with a/6. It's sat more than not over its life, when I got it the front car was disintegrated and the guts were blocking the rear cat. I got it running long enough to sell that original engine. I rebuilt another one I have and put that one in. Older forged crank version.
Anyway I put a super 6 setup on it and wallowed out the exhaust outlet to match the gasket and the flange I bought, for the eventual new outlet to tail exhaust. It was way small compared to a fel pro /6 stock replacement flange gasket
It isn't anymore.
For the exhaust I started with a stub off of a super 6 setup and then I raided an exhaust shop scrap dumpster (I checked with the owner beforehand) and got most of what looked like brand new mandrel bent piping, wasn't even hardly tarnished.
I thought I was piecing a temporary system together to get it to the exhaust shop. It looks good enough it might stay and I'll just get a new muffler and tail off of what I started with and call it good. It helps that I have a 2 post lift in my garage at home and a better than decent MIG welder.... At least I didn't have to weld this one up with a torch and a coat hanger.... I've actually done that one more than once over the years...

 

[slantsixdan]

If you're doing up a truck/van exhaust system, the hot ticket is a Walker № 50051 muffler. Hemi Dodge Ram item. Lotsa flow, plenty quiet.

 

[timk225]

Has anyone done testing to see how much HP the stock exhaust manifold can handle before becoming a restriction in a naturally aspirated system? I've seen them used in turbo applications, so I guess they can flow well enough, but that's with the whole system under pressure.

 

[timk225]

I put my order in today for the TTI 2-1/2" exhaust system to bolt up to the /6 exhaust manifold, $622 including the $138 UPS wants to haul it across the country!

I will "improve" the exhaust manifold with some grinding when I put the 2 bbl Holley 350 on. Haven't decided yet on pulling the head off for further porting, and new seals and valve springs and cut it about 0.080" or so. Might as well do it all at once!

And I'd like to put in an RV-10RDP cam while I already have the engine apart. Surely it'll need a new timing chain assembly. And a baffle in the oil pan, maybe a crank scraper, port the oil pump passages.......

 

[RustyRatRod]

I put my order in today for the TTI 2-1/2" exhaust system to bolt up to the /6 exhaust manifold, $622 including the $138 UPS wants to haul it across the country!

I will "improve" the exhaust manifold with some grinding when I put the 2 bbl Holley 350 on. Haven't decided yet on pulling the head off for further porting, and new seals and valve springs and cut it about 0.080" or so. Might as well do it all at once!

And I'd like to put in an RV-10RDP cam while I already have the engine apart. Surely it'll need a new timing chain assembly. And a baffle in the oil pan, maybe a crank scraper, port the oil pump passages.......

Hopefully, you ordered it straight from TTI and not from Mancini.