Exhaust Manifold Mod

[andrew3408]

I agree with the DIY thing i am going to do my ex manifold for my 170 build. and use the tti 2.5 ex head pipe and mid pipe and i got a 2.5 magna flo muffler to go on it. headers for these things are way over price now days..

 

[Cruisingram]

Have you priced headers for a slantie yet?

If your ok spending that kind of dough, go for it

But if you were to calculate HP/dollar you'd get a much higher return on the DIY approach

Yeah, they want like twice what my BB mopar baddies are LOL. Looks like grindah for me

 

[Dart/Valiant]

Someone knows what's the diameter of those two bolts? Gasket is Fel-pro 9547 but I need to find the correct flange for the front pipe.

 

[volaredon]

7/16" studs (NOT the wrench size!!!!)

 

[CichliDart]

Hey Rusty,
You give this a try yet?

 

[Charrlie_S]

100 cc improvement over the whole manifold? What a waste of time and effort. Better off just opening up the outlet diameter.

 

[CichliDart]

100 cc improvement over the whole manifold? What a waste of time and effort. Better off just opening up the outlet diameter.

How about both?

 

[volaredon]

That would definitely work

 

[RustyRatRod]

100 cc improvement over the whole manifold? What a waste of time and effort. Better off just opening up the outlet diameter.

I kinda thought the same thing, but people gotta try new things. Nothin wrong with that.

 

[Charrlie_S]

I kinda thought the same thing, but people gotta try new things. Nothin wrong with that.

I could see the sense in doing this, if racing in a class that required stock manifolds. Every little bit helps. But on a "street car" too little gain for the effort. I would bet that over the surface area of the inside of the manifold, that 100 cc's would only amount to a few thousands of an inch removed.

 

[slantsixdan]

Y'all reminding me of the "extrude hone" process that had a moment in the sunshine of various magazines thirty years ago. Looks like it's still a thing. But boy, it'd make a hassle with the heat control valve: dismantle, which requires destruction…protect bushings…then reassemble with new parts which would require hunting down expensive/scarce NOS parts. This same hassle would exist with "acid porting", which is a remarkably bad idea unless you have a kink for Slant-6 manifold R&R jobs. Acid does a nasty thing to ferrous metal, called hydrogen embrittlement. Don't nobody need their Slant-6 exhaust manifold getting more prone to cracking!

I can imagine a measurable, practically meaningful flow increase at high RPM with extrude honing, but not with that acid silliness.

 

[MadScientistMat]

I get the impression the main reason for acid porting is that it's a lot harder for tech inspectors to notice it in races that don't allow porting.

 

[timk225]

Has anyone ever flow bench tested the stock exhaust manifold to see what it can flow stock vs modified?

 

[Killer6]

I get the impression the main reason for acid porting is that it's a lot harder for tech inspectors to notice it in races that don't allow porting.

And that's precisely the target of that technique, looking for all the world you didn't just do what you're specifically forbidden to do per the rules......"just got lucky finding a bigun".....

 

[Charrlie_S]

And that's precisely the target of that technique, looking for all the world you didn't just do what you're specifically forbidden to do per the rules......"just got lucky finding a bigun".....

Does anyone know of any performance venue that requires stock manifolds? I don't. To me, it just looks like another solution looking for a problem.

 

[volaredon]

Not the racetrack but maybe certain classes of racing?

 

[Killer6]

Yes, of course class racing teardown insp., not track safety insp.

 

[Charrlie_S]

Back in the early '70's NHRA required stock manifolds in "stock eliminator", but not since then. Does anyone know of any racing class that requires stock exhaust manifolds?

 

[RustyRatRod]

Does anyone know of any performance venue that requires stock manifolds? I don't. To me, it just looks like another solution looking for a problem.

I don't think even stock eliminator requires manifolds, does it? Maybe some of those FAST classes. "Factory appearing stock tire"I think it is.

 

[RustyRatRod]

Back in the early '70's NHRA required stock manifolds in "stock eliminator", but not since then. Does anyone know of any racing class that requires stock exhaust manifolds?

While more expensive, I think the extrude hone process would work much better for limitations to stock manifolds. But if they have restrictions to inlet and outlet sizes, you'd be taking a chance.

 

[volaredon]

Well, I'm thinking the tiny outlet size on these has at least a little bit to do with sloppy tolerances, tolerance stacking, etc. Just like how deck height is usually actually taller than spec.
Especially when most stock exhaust pipes are larger than the outlet. Just the simple fact that they aren't close to the same as gasket) flange size bears that out.
When I did my manifold hog out, the hole was not only much smaller but not even centered within the confines of the gasket/ flange configuration.
The gasket touched the side of the hole in one spot, and across from it I had to take out at least 1/4", maybe closer to 3/8" to get the hole out to match the gasket. Id have thought it would have been more centered.
I wonder what "blueprint spec" was on the outlet diameter back then... Or if there was such a spec?

 

[RustyRatRod]

Well, I'm thinking the tiny outlet size on these has at least a little bit to do with sloppy tolerances, tolerance stacking, etc. Just like how deck height is usually actually taller than spec.
Especially when most stock exhaust pipes are larger than the outlet. Just the simple fact that they aren't close to the same as gasket) flange size bears that out.
When I did my manifold hog out, the hole was not only much smaller but not even centered within the confines of the gasket/ flange configuration.
The gasket touched the side of the hole in one spot, and across from it I had to take out at least 1/4", maybe closer to 3/8" to get the hole out to match the gasket. Id have thought it would have been more centered.
I wonder what "blueprint spec" was on the outlet diameter back then... Or if there was such a spec?

I've read all along that "supposedly" the Super Six two barrel option got a larger outlet exhaust manifold, but to date, I've never seen one. Also, I've seen people say that some Super Six packages got a larger 2.250" head pipe. I've never seen one. Not to mention that makes zero sense to put a bigger head pipe on and not have a larger outlet manifold. So are both those stories myths? Maybe @slantsixdan can help us out with it. I've seen him talk about it before, but naturally, my memory doesn't recall what he said. Dan you out there? Breaker 1-9

 

[Charrlie_S]

I've read all along that "supposedly" the Super Six two barrel option got a larger outlet exhaust manifold, but to date, I've never seen one. Also, I've seen people say that some Super Six packages got a larger 2.250" head pipe. I've never seen one. Not to mention that makes zero sense to put a bigger head pipe on and not have a larger outlet manifold. So are both those stories myths?

To the best of my knowledge there is no difference in the exhaust manifold. I don't have a parts manual for the years they had the super six, so I can't check part numbers, but it is entirely possible the SS got a larger exhaust pipe/system (the manifold outlet is larger than the standard pipe). After this many years it is possible most if not all systems could have had the pipe replaced and the standard pipe used. As you said, maybe Dan can clarify.

 

[RustyRatRod]

To the best of my knowledge there is no difference in the exhaust manifold. I don't have a parts manual for the years they had the super six, so I can't check part numbers, but it is entirely possible the SS got a larger exhaust pipe/system (the manifold outlet is larger than the standard pipe). After this many years it is possible most if not all systems could have had the pipe replaced and the standard pipe used. As you said, maybe Dan can clarify.

I don't think there is either, Charlie....although I've seen people say it. I've never seen one. Course, that means nothing, too. LOL

 

[MadScientistMat]

Does anyone know of any performance venue that requires stock manifolds? I don't. To me, it just looks like another solution looking for a problem.

Some autocross and road race entry level classes mandate stock manifolds. But if you're winning one of those enough with a slant six to get protested, people are going to be accusing you of witchcraft instead of porting your exhaust manifold.