2 barrel with stock exhaust??

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Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
Joined
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I have 72 demon with an offy 4 barrel manifold and 4 barrel carb. I personally feel the 4 barrel is a waste with the stock exhaust but it was set up like that before I got the car. It runs but not very good but it really needs a tune up.


So I am thinking to replace the 4 barrel setup with a 2 barrel set up and replace the timing chain and tune it up. I am not sure if even the 2 barrel set up would be a waste on the stock exhaust. However I do not have headers and headers are not currently in the budget.

Would a 2 barrel have any or much more scoot over a 1 barrel with the stock exhaust?

The car has the original 7.25 rear and floor shifted 3 speed manual with 195/70 R14s, everything is pretty much stock.
 
Rainy Day Auto said:
I have 72 demon with an offy 4 barrel manifold and 4 barrel carb. I personally feel the 4 barrel is a waste with the stock exhaust but it was set up like that before I got the car. It runs but not very good but it really needs a tune up.


So I am thinking to replace the 4 barrel setup with a 2 barrel set up and replace the timing chain and tune it up. I am not sure if even the 2 barrel set up would be a waste on the stock exhaust. However I do not have headers and headers are not currently in the budget.

Would a 2 barrel have any or much more scoot over a 1 barrel with the stock exhaust?

The car has the original 7.25 rear and floor shifted 3 speed manual with 195/70 R14s, everything is pretty much stock.
Click to expand...

It has been my experience on two different slants that a two bbl is an improvement over a one barrel even with stock exhaust.
I am sure others will pipe in with comments but from what I have read a single exit pipe performs better than duals, but a slightly larger diameter exhaust may be an improvement. Maybe better with dual exhaust from the head and into a y pipe a few feet down.

YMMV.

Mike
 
2bbl is better than a 1bbl and a 6 into 1 makes the most power and is also the cheapest.
 
You could do like I plan on and open up the outlet on the exhaust manifold some. There's enough meat there to open it up, just probably not all the way to the 2.25" Super Six size, but there is room for improvement. I do agree though, that the two barrel will likely be an improvement even with the stock size exhaust. But even the factory put the 2.25" pipe against the stock manifold, so they must have known something.
 
Rainy Day Auto said:
I have 72 demon with an offy 4 barrel manifold and 4 barrel carb. I personally feel the 4 barrel is a waste with the stock exhaust but it was set up like that before I got the car. It runs but not very good but it really needs a tune up.


So I am thinking to replace the 4 barrel setup with a 2 barrel set up and replace the timing chain and tune it up. I am not sure if even the 2 barrel set up would be a waste on the stock exhaust. However I do not have headers and headers are not currently in the budget.

Would a 2 barrel have any or much more scoot over a 1 barrel with the stock exhaust?

The car has the original 7.25 rear and floor shifted 3 speed manual with 195/70 R14s, everything is pretty much stock.
Click to expand...
I wouldn't give up on the 4 barrel set you have yet........
What it needs is more flow out of the exhaust to make it work well.
Seeing that you are a hands on type of lady that knows how to weld and tinker with things, I wouldn't hesitate to take the exhaust manifold off and ''split'' it, that would give you a lot more exhaust flow and if you don't want to do that, take Rusty's advice and hog out the exhaust and put a bigger head pipe on.
There's lots of info on slant6.org on how to do this.
This is a lot like ''Dutra Duals'' except a lot cheaper.

Also, the carb on the 4 barrel intake should be small, say no more than 400 cfm for it to work on the slant.
A friend of mine had roughly the same set up as you and it worked well and I bet he gained 40 horses over the stock 1 barrel and the stock exhaust.
You really could feel the difference.
Of course, the tune up has to be addressed first........
 
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Rainy day, I own a '70 challenger with 225 Slant6 power. Back in the 90's I decided to install the Super Six 2bbl set up for a little more kick. Internally a stock configurated engine, except with the 280 CFM carb, Carter BBD. After that I added Hooker 3 into 1 headers w/ real 2 1/4" aluminized dual exhaust w/ "H" pipe to the back, and 2 glass pack mufflers. Mopar elect. Ign. with orange box w/ high output coil. Open element K&N 14x3 air cleaner and filter. I think it runs pretty good and sounds great at the back. Been running this setup for many years with , no problems. Thanks, Al
 
Oh, I forgot to mention Rani, that the 2 barrel super 6 set up is a good option if you don't want to split the exhaust manifold and just hog out the original one and put on a bigger head pipe.
I would trade you heads up for your 4 barrel set up fo a super 6 set up I have.
Too bad you are so far away.
I sure wish I could talk to you on the phone some day........
 
I installed a SS 2bbl onto a 9.5 Scr,slanty with a small solid-lifter cam, with the original single exhaust, And as far as I could tell it was no quicker, if not slower than the preceding 8.0Scr, single barrel, hydraulic cam combo.
However I was not looking for performance with this combo, rather fuel-economy; and to that end it was quite successful.
The point is this; the stock exhaust system sux
 
RustyRatRod said:
There's enough meat there to open it up, just probably not all the way to the 2.25" Super Six size
Click to expand...

Not sure if this helps the discussion or not but I have two Super Six exhaust manifolds, they both measure 2.00" ID where the down pipe bolts on. The factory muffler pipe is also 2.00" ID. There is some extra material in the manifold exhaust port, but it would take a far better person with a die grinder than myself to hog out the ID to 2.25". The smallest OD I measure on the manifold exit is 2.61". That means there would be a hair over 1/8" wall thickness after taking this out an extra 0.25". I will be leaving this alone, as a look inside the manifold doesn't appear to have a lot of options to open it up. Maybe a stock slant manifold would be different, but that's what I know about a Super Six. This came off a 78 Volare I took apart a few weeks ago, and that 2" pipe goes all the way to the muffler. I have no idea what size pipe goes from the muffler to the rear tail pipe, this car had nothing behind the muffler.

I won't have any real-world suggestions until spring, when my Valiant is reborn. But I read a lot on this site and dot org. What I gather from the slant gurus is better breathing in and out is vital to performance. A dual exhaust manifold setup (Dutra Duals or a homemade version of the same, or headers) going into a wye then to the muffler and out the back as a single exhaust is the way to go, and it's what I'm going to do.

My current set-up is a one-barrel into a stock exhaust, but my pipe beyond the manifold is scrawny, like 1-5/8" or so if I recall correctly. If I had your scenario I would at the least either try to hog out the stock manifold or find/make a dual manifold into a single 2.0-2.25" pipe to the rear bumper. If you could find a Super Six exhaust you'd be ahead of the game. And yes, everything I know says a 2-barrel is a better deal. Good timing and tuning should make a noticeable difference.
 
I've seen people chop the outlets off of manifolds and weld on just a steel piece of muffler pipe a larger diameter with a flange on it in the same location as the original but just larger. Seen some really crappy jobs, but seen some really good jobs done, too. For all that time and trouble, you should just get headers or do the split manifold or the Dutra Dual$$$$$
 
I got a List #7455 4360 Economaster carb for you hard up 4bbl slant people. Its tiny, 450 CFM with a wide spreadbore primary spacing, but a square butterfly pattern. Been hanging on wall forever for a 273 build but changed directions. Holley denies existance but the kits are out there.....renew kit is 37-1540, acc pump is 135-1.. pic from an IH site. Maybe Ill fab up a slant sheetmetal intake for this orphan.
031808_carb-jpg.jpg
 
I think the 'Super Six exhaust' is a myth. My 79 Volare wagon came with the super six slant and the exhaust manifold and exhaust pipes were small, definitely nothing like 2 1/4. I ground out the exhaust manifold to 2 1/4 myself and welded up my own 2 1/4 exhaust all the way back. It made a difference you could feel and I would do it again on my next wagon.
To the OP, You should give the car a good tune-up, adjust the valves, set the timing, etc and then see where you stand with things. If it runs to your liking, great, if not you should be able to switch to a two barrel setup easy enough.
 
pishta said:
I got a List #7455 4360 Economaster carb for you hard up 4bbl slant people. Its tiny, 450 CFM with a wide spreadbore primary spacing, but a square butterfly pattern. Been hanging on wall forever for a 273 build but changed directions. Holley denies existance but the kits are out there.....renew kit is 37-1540, acc pump is 135-1.. pic from an IH site. Maybe Ill fab up a slant sheetmetal intake for this orphan.
View attachment 1715429100
Click to expand...

Yeah those are unique to say the least. Might work good on a slant.
 
Badvert65 said:
I think the 'Super Six exhaust' is a myth. My 79 Volare wagon came with the super six slant and the exhaust manifold and exhaust pipes were small, definitely nothing like 2 1/4. I ground out the exhaust manifold to 2 1/4 myself and welded up my own 2 1/4 exhaust all the way back. It made a difference you could feel and I would do it again on my next wagon.
To the OP, You should give the car a good tune-up, adjust the valves, set the timing, etc and then see where you stand with things. If it runs to your liking, great, if not you should be able to switch to a two barrel setup easy enough.
Click to expand...
some came with bigger outlets some did not.
 
halfafish said:
Not sure if this helps the discussion or not but I have two Super Six exhaust manifolds, they both measure 2.00" ID where the down pipe bolts on. The factory muffler pipe is also 2.00" ID. There is some extra material in the manifold exhaust port, but it would take a far better person with a die grinder than myself to hog out the ID to 2.25". The smallest OD I measure on the manifold exit is 2.61". That means there would be a hair over 1/8" wall thickness after taking this out an extra 0.25". I will be leaving this alone, as a look inside the manifold doesn't appear to have a lot of options to open it up. Maybe a stock slant manifold would be different, but that's what I know about a Super Six. This came off a 78 Volare I took apart a few weeks ago, and that 2" pipe goes all the way to the muffler. I have no idea what size pipe goes from the muffler to the rear tail pipe, this car had nothing behind the muffler.

I won't have any real-world suggestions until spring, when my Valiant is reborn. But I read a lot on this site and dot org. What I gather from the slant gurus is better breathing in and out is vital to performance. A dual exhaust manifold setup (Dutra Duals or a homemade version of the same, or headers) going into a wye then to the muffler and out the back as a single exhaust is the way to go, and it's what I'm going to do.

My current set-up is a one-barrel into a stock exhaust, but my pipe beyond the manifold is scrawny, like 1-5/8" or so if I recall correctly. If I had your scenario I would at the least either try to hog out the stock manifold or find/make a dual manifold into a single 2.0-2.25" pipe to the rear bumper. If you could find a Super Six exhaust you'd be ahead of the game. And yes, everything I know says a 2-barrel is a better deal. Good timing and tuning should make a noticeable difference.
Click to expand...
You hog it out with a hole saw. stack the 2”inside the 2-1/4” and carefully ream away. I have enlarged holes in steel parts many times using this method.
 
2bbl on my flattie
7641328A-CB82-433D-B302-AF0B2C9FF067.jpeg
That was tacked for a test fit.
 
Hole saws are stackable, no? well thread the arbor into them both. Smaller one serves as a pilot.

Lets say you made a hole 1-1/2”,realized its too small. How do you make it larger when pilot for hole saw is gone. Use the 1-1/2” as the pilot and thread it into the one you need. Works slick.
 
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