Exh manifolds in an Early A...

[Cuda416]

My son and I found and bought a set of exhaust manifolds on a 65 Dart with a 273 we are planning on using on his magnum swap since headers are just too pricey for this right now. We realize headers will be WAY better, but we're just trying to get this running for now.

We located some drivers side 72-74 340 manifolds on a couple of darts with 318's. Casting numbers checked out. Pass side are 318 castings.

1. Will the 72-74 340 manifolds "fit" like the 273 units in an early "A". They look very similar.
2. Safe to say the the manifolds from the 318 will flow better, even if slightly?
3. I can get them for $45 ea. Worth it?

Now, finally, we are using a 2.5" exhaust kit meant for use with heads and need to fab up some short pieces to go from the exhaust manifolds to the pipes where the flanges would normally meet up with headers.

If you've done this, what parts did you use or cut up to make up head tubes? They both will need a couple of tight bends it seems so I'd rather stack the deck in my favor of getting it right the first time if possible. Worst case, we'll use flex tube until we can do better but I'd rather not.

Thanks!

 

[Syleng1]

340 manifold on early abody is not a good combo. Binds up at steering column.

Never modified one but the factory early a- exhaust manifold for drivers side is the best route. But very restrictive for anything but a 273 stock motor. People use it all the time but I’m just saying it could be better.

I used the 2.50” tti exhaust for the stock manifolds (273) and duals making the needed mods to the transmission mount. I’ll see if I can add pictures.

 

[Cuda416]

340 manifold on early abody is not a good combo. Binds up at steering column.

Never modified one but the factory early a- exhaust manifold for drivers side is the best route. But very restrictive for anything but a 273 stock motor. People use it all the time but I’m just saying it could be better.

Thanks, this is the kind of info I'm looking for in that regard. We have the 273 units and agree, not the best for performance, but at this point, we're just trying to get something put together to drive.

 

[Treblig]

The 68/69 340 driver's will work, it's designed differently from the 70s 340 driver. You could sell the one you have and buy the other. You're in Texas, so am I, I have a couple of 70s 340 passenger's manifolds if you want to buy one for a real good price. You can also find a 96/97/98 Jeep Grand Cherokee 318/360 magnum passenger's manifold. Some FABO members have did a little grinding on the magnum passenger manifold to clear the inner fender on the '65 bodies. The Jeep manifold has an outlet hole (2 1/8" almost as big as the 340 driver.
The magnum and the 340 manifolds have magnum type exhaust port shape as opposed to the early (67-early70s 318)

 

[chryslerfat]

The left manifold will work with manual steering but will not work if you have power steering. Simple as that.

 

[Cuda416]

The left manifold will work with manual steering but will not work if you have power steering. Simple as that.

This helps too since we don't have P/S.

 

[Cuda416]

View attachment 1715327838 340 manifold on early abody is not a good combo. Binds up at steering column.

Never modified one but the factory early a- exhaust manifold for drivers side is the best route. But very restrictive for anything but a 273 stock motor. People use it all the time but I’m just saying it could be better.

I used the 2.50” tti exhaust for the stock manifolds (273) and duals making the needed mods to the transmission mount. I’ll see if I can add pictures.

We modded the crossmember for duals, so we're half way there. Just need to get from the exhaust manifold flanges down to the jegs 2.5" kit. I realize if we stick with the 273 manifolds, we are going from 1-7/8 to 2.5 so we'll be playing step up games.

 

[Treblig]

We modded the crossmember for duals, so we're half way there. Just need to get from the exhaust manifold flanges down to the jegs 2.5" kit. I realize if we stick with the 273 manifolds, we are going from 1-7/8 to 2.5 so we'll be playing step up games.

You will be going from 1 5/8" to 2.5, the resistance to flow is proportional to one over the radius squared, so if the radius (or diameter) is cut in half, the velocity of the fluid will decrease by a factor of 2^2 or a factor of 4. So in a pipe 1/2 as large, 2.5" down to 1.25", flow will decrease 4 times. This is true for fluids in a pipe I'm not sure about air flow but I do know it decreases dramatically.

 

[Cuda416]

You will be going from 1 5/8" to 2.5, the resistance to flow is proportional to one over the radius squared, so if the radius (or diameter) is cut in half, the velocity of the fluid will decrease by a factor of 2^2 or a factor of 4. So in a pipe 1/2 as large, 2.5" down to 1.25", flow will decrease 4 times. This is true for fluids in a pipe I'm not sure about air flow but I do know it decreases dramatically.

Just to stir the pot, velocity, flow past a point and "volume" are all different parts of the same thing. I'm only thinking out loud, not a flow export but it "seems" that, yes, the velocity would decrease, and the flow past a point would decrease due to the enlarged cross section. A river passing a million gallons of water over a rapids, still passes a million gallons of water at a wider point, it is just spread out. The total volume of water is the same. No?

So yes, I agree the flow rate at a wider cross section will be slower but the volume of gas should remain the same?

 

[Treblig]

Here's a chart showing natural gas flow through different pipe diameters. You can see that in a 10 foot length of pipe 2" in dia. decreases from 4020 cf/hr down to 678 cf/hr in a 1" dia. pipe.:

 

[Cuda416]

Here's a chart showing natural gas flow through different pipe diameters. You can see that in a 10 foot length of pipe 2" in dia. decreases from 4020 cf/hr down to 678 cf/hr in a 1" dia. pipe.:

View attachment 1715327890

I understand the difference between the pipe cross section affecting flow, but your original assertion is saying that going from a smaller pipe to a larger one will somehow reduce the flow rate. This chart doesn't say, going from a smaller one to a larger one does anything. if anything, this chart supports the opposite.

 

[Treblig]

Sorry, my point was that no matter how much flow the larger pipe gives you the smaller 1 5/8" pipe will restrict (control the flow) in the end. What I'm trying to say is that you could put a 4" pipe behind the manifolds and it won't make much difference because the manifolds are the biggest restriction in the exhaust system. I know you have to do what you have to do, just trying to help with info. treblig

 

[Cuda416]

Sorry, my point was that no matter how much flow the larger pipe gives you the smaller 1 5/8" pipe will restrict (control the flow) in the end. What I'm trying to say is that you could put a 4" pipe behind the manifolds and it won't make much difference because the manifolds are the biggest restriction in the exhaust system. I know you have to do what you have to do, just trying to help with info. treblig

Ahh, sure man, no problem I understand now. You are 100% correct. I wasn't trying to argue, just "understand". The 2.5" pipe wasn't to get more performance at this point, just get gasses from the front of the car to the back of the car. it was a relatively cheap setup that came with almost everything we needed minus the header-flange to exhust-flange portion. At some point when he decides to install headers, if he can afford them, he'll be all set.

I appreciate the comments man, I'm always learning. (or trying to).

-=C

 

[Cuda416]

Ok, assuming the steering clearance isn't a concern, does anyone know the outlet size of the 72-74 340 exhaust manufolds? Any difference on the pass side? The two I know of are on 318's. I've read that at that time, it was sort of a crap shoot as to what you got on the drivers side with the 318.

Whoops, never mind, it was already pointed out by @Treblig it's at least 2-1/8 and dag gum if google doesn't say 2-1/4" .

 

[Treblig]

Yes the 340 driver is actually 2 1/4". The 60s 340 passenger is 2 1/4". The Jeep magnum is 2 1/8". The 70s 340 passenger is 1 7/8". The 273/318 are 1 5/8"....I've never had a 273 manifold so it could be smaller than 1 5/8"????.

 

[Cuda416]

Yes the 340 driver is actually 2 1/4". The 60s 340 passenger is 2 1/4". The Jeep magnum is 2 1/8". The 70s 340 passenger is 1 7/8". The 273/318 are 1 5/8"....I've never had a 273 manifold so it could be smaller than 1 5/8"????.

The ones I found are casting number 3614395 (71-73 340).

I've seen those listed as both 72-73 318's and later 71-73 340's parts . Can anyone confirm or deny? If they are correct on a 340, then they should be 1-7/8?

 

[Cuda416]

Yes the 340 driver is actually 2 1/4". The 60s 340 passenger is 2 1/4". The Jeep magnum is 2 1/8". The 70s 340 passenger is 1 7/8". The 273/318 are 1 5/8"....I've never had a 273 manifold so it could be smaller than 1 5/8"????.

Have a casting number for the Jeep magnum manifold?

 

[Treblig]

The one in the first pic (top manifold) should be the 340 one you have. the first pic (lower manifold) is the magnum:

Closer pic of Jeep magnum:

Closer pic of Jeep magnum:

 

[66jim]

Use what manifolds you have on hand. Spend spare hours with a carbide bit and
enlarge and match up the ports and the outlet as deep as you can. Dyno test was
written on SBM manifolds and the differences in output did not amount to a dime. People
still chasing 340 manifolds as a myth for big bucks. If you after very high RPMs
its different then just get headers.

 

[Cuda416]

Use what manifolds you have on hand. Spend spare hours with a carbide bit and
enlarge and match up the ports and the outlet as deep as you can. Dyno test was
written on SBM manifolds and the differences in output did not amount to a dime. People
still chasing 340 manifolds as a myth for big bucks. If you after very high RPMs
its different then just get headers.

I'm just trying to not choke this thing to death, lol..

 

[66jim]

I'm just trying to not choke this thing to death, lol..

Whats the engine? If its a 416 like your handle and your dead set against headers. ,
then I would get the best flowing SBM manifolds and port the crap out of them. Got
a 300hp or less use what you got.

 

[Cuda416]

Whats the engine? If its a 416 like your handle and your dead set against headers. ,
then I would get the best flowing SBM manifolds and port the crap out of them. Got
a 300hp or less use what you got.

No, this is my kids car. 65 Valiant with a 5.9 magnum. Not dead set, just can't afford...

 

[66jim]

For me thats kind of a boarder line situation with a 5.9, If the 5.9 is going to stay
stock the for me I would port the 273 manifolds, much more than stock or future
upgrades use 273s and save for headers. Manual steering has more room for cheap
spitfire type headers.

 

[Cuda416]

For me thats kind of a boarder line situation with a 5.9, If the 5.9 is going to stay
stock the for me I would port the 273 manifolds, much more than stock or future
upgrades use 273s and save for headers. Manual steering has more room for cheap
spitfire type headers.

Which "cheap spitfire headers" are you referring to?

 

[66jim]

Which "cheap spitfire headers" are you referring to?

Only type (Tri Y) being made I know of are old Spitfire design made years ago by
an guy named Harold in his back yard. Now Laysons is making them I believe
they are 4-5 hundred bucks? Sometimes posters have said there are discounts
available for Dougs headers thru Auto Zone I think. Anyhow Dougs are very nice.
They will cost a bit more as they are better than the Laysons.