Magnum Exhaust Manifolds in an A Body

[dustoff440]

Heres the dyno tests on the manifolds

http://www.moparts.org/Tech/Archive/exhaust/9.html

As you can see there isnt much of a difference between the magnum and 340 manifolds.

I cant find it again but I saw a chasis dyno test on a 340 in a Duster which had mild "plus" engine and there was only 20 horsepower between the headers and the 340 and mag manifolds

Also have seen where a couple of guys have installed mag manifolds in a bodies with MANUAL steering where there was some massaging and grinding but had a sucessful install. I have NOT seen a manifold with power steering without there having been major frigging and grinding.

 

[kujo]

Just looked at the dyno results that dustoff440 posted and they didn't even flow the left side magnums. Also, didn't post whether they were the big port or small port magnums. Bummer. It would have been nice to be able to compare everything.

 

[jim ayers]

I am getting my 340 ready to place in my 69 barracuda and a big chunk of my passenger side exhaust manifold just fell off (an old crack). I am not a header kind of guy so I am interested in using magnum exhaust manifolds. My car is manual steering, so I am clear there, but what about my manual transmission z-bar? Will it interfere?

thanks

 

[kujo]

I am getting my 340 ready to place in my 69 barracuda and a big chunk of my passenger side exhaust manifold just fell off (an old crack). I am not a header kind of guy so I am interested in using magnum exhaust manifolds. My car is manual steering, so I am clear there, but what about my manual transmission z-bar? Will it interfere?

thanks

The Magnum manifold dumps right where the z bar is. You'll need a hydraulic clutch setup to run a manual trans.

 

[kujo]

I test fitted my driver side manifold with Flaming River manual gearbox to power steering coupler and there's still some interference. Not a lot but still some. One area is where the transmission gear select lever arm is (column shift) I've since cut that section of the gear shift tube off (not pictured) another area is the manual gearbox just contacts the bottom of the manifold. Very little grinding to the manifold should fix this. And last the allen set screws on the coupler. One of the screws clears fine and the other hits the bottom of the manifold. I'm going to drill an indent in the shaft to sink the screw into this should take up the amount required to clear the manifold when the steering wheel is turned.

 

[Karl M]

So for you guys that have settled on paying for a left side factory A body 340 manifold, due to power steering fitment issues, what part # is it?

Karl M.

 

['Mad Max']

...so this is an old thread but man is it a good one - very valuable and even in 2023 still very relevant intel on the pros and cons of running small block magnum exhaust manifolds in an A-body. I am pondering this very thing for my build now, and wanted to respond with a quick recap to make sure I got it all right, and to ask if there have been any fresh solutions to the three big issues.

I'm building a 71 Demon (based on a 73 Duster chassis). It will have a nice warm Magnum 318 and an 833od 4-speed - OE heads. It will have power steering, and hydroboost brakes.

As I understand from the wealth of info in this thread, when trying to bolt up a drivers side magnum exhaust manifold to a magnum or LA small block, there are three major interference issues:

1) power steering gearbox
2) the steering column
3) the z-bar

Seems running manual steering resolves the gearbox interference problem, but some grinding is still necessary for the column.

Seems using a standard set of 340 manifolds will resolve all the issues, tho there will be a large disparity between the 340 and magnum exhaust port sizes.

Q1 - Would running 340 manifolds on a magnum head induce legit high-rpm flow problems...or is that not a thing?

Q2 - Is there a proven rack and pinion steering conversion for the A-body's? I looked around and haven't yet found something that is a bolt-in and proven solution. I'm not apposed to going with an aftermarket K-frame and rack n pinion steering if that resolves the steering problems, but I don't want to do a full aftermarket front suspension setup in order to get r&p steering.

Q3 - Will using a hydraulic clutch resolve the 4-speed linkage problem?

...or just pony up the $ for 340 manifolds and fugetaboutit...

Thanks,
- Sam

 

[Cuda416]

I put the 2-1/8 magnum manifolds in a 1964 dart.
No power nothing and a pushbutton 904. I had to cut the steering collumn, work and weld on my flaming river conversion kit and also had to do a little grinding at the driverside manifold. It took me two days to build the tubings, but now it fits all nice and tight.

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Any chance of seeing how your pipes fit under the car? I'm about to do the same thing.

 

['Mad Max']

...maybe 318 manifolds...

So to recap, I'm building a fun 71 Demon. Dropping in a nice warm magnum 318, with a 4bbl and nice '340' cam, and an A-833od 4-speed, and 3.23 gears - just a nice clean-running hot street machine that cruises perfectly on the highway and idles with a bit of lope - probably a 5500 rpm limit. Looking at the Whiplash cams from Hughes. Could care less about the engine making 'maximum power' - all I care about is the engine making nice power without sacrificing streetability and don't want it to be overly smelly - no 108* cams, and no headers - want things OE-looking and OE-sealing. That said, here's some additional thoughts on suitable exhaust manifolds.

To me I basically have three options: 1) '02 Magnum manifolds, 2) 340 manifolds, and 3) 318 manifolds.

The magnum manifolds have significant physical interference issues with factory A-body power steering, steering columns (all), and z-bar linkage. I am probably going to run a hydraulic clutch setup which I think will cure the z-bar problem, but unless I can find a nice aftermarket K-frame setup with power rack and pinion steering I am not seriously considering magnum manifolds.

340 Manifolds would flow more than enough...but I'm not convinced I will 'need' 340 manifolds....and for darn sure I don't want to pay the huge $$$ for them.

So...why not 318 manifolds. Check out the port sizes in the below pic. The 318 manifold ports match the magnum head exhaust ports perfectly - the port sizes are almost exact. That alone indicates to me that 318 manifolds 'match' magnum 318 head ports, and that has to count for something. 340 manifold ports are HUGE compared to magnum ports...which IMO also probably means the huge ports and internals are likely 'unnecessary'. I already have a set of 318 manifolds...and so I am seriously considering running them.

The car I'm cloning had a warm LA 318 with 360 heads, and I think I had 340 manifolds on it - I honestly don't remember, but they were either 318 or 340 manifolds, but definitely wasn't headers. The thing ran great. Assuming the same cam profiles, I'm inclined to think an LA 318 w/ 360 heads and 340 manifolds would run nearly identically as a similar magnum 318 with LA 318 manifolds, or at least so closely the same that I'd never notice the difference...at least not at/under 5000 rpm. I offer this idea to the congregation for y'alls thoughts.

 

[Cuda416]

Two problems.

1. Not sure you can determine the port size form the gasket alone.
2. The port you care about for performance, is the outlet. The 340 and "good" magnum manifolds have the larges outlet.

Sounds like you've already talked yourself into using 318 manifolds, so carry on and enjoy.

 

['Mad Max']

...fair points about the inlet and outlet ports. I'm pulling the 318 manifolds off today and will measure the outlet port sizes, and I'll measure the head port sizes for comparison. Hopefully the outlets are at least the same as the 1-7/8" magnum outlets.

 

[Cuda416]

...fair points about the inlet and outlet ports. I'm pulling the 318 manifolds off today and will measure the outlet port sizes, and I'll measure the head port sizes for comparison. Hopefully the outlets are at least the same as the 1-7/8" magnum outlets.

The "good" magnum manifolds have 2-1/8" outlets. Just a tad smaller than late 60's 340.

 

['Mad Max']

yep copy - while I do have a set of those the interference with the power steering box is a non-starter...plus if I have the choice I'd really like to have era-matching manifolds

 

[Cuda416]

yep copy - while I do have a set of those the interference with the power steering box is a non-starter...

Also a fair point.

 

[DionR]

Seems using a standard set of 340 manifolds will resolve all the issues, tho there will be a large disparity between the 340 and magnum exhaust port sizes.

Be aware that some Magnum heads don't have enough material around the port to seal a 340 exhaust manifold. Not all, but my R/T heads and some OEM heads I have seen can be a problem.

340 exhaust manifolds

Which set of 340 exhaust manifolds work best for the magnum swap. There appears to be several versions of these manifolds. Does the drivers side one that exits right top rear the best. A pic of what you used would help.

www.forabodiesonly.com

 

[DionR]

Personally, I don't want to give anything up I don't have too. So, if it were me, I would run a 340 DS manifold and an early Jeep PS manifold.

The DS 340 manifold is cheap(er) when compared to the PS free flow since they made the same DS manifold from '68-74, but the good PS manifold was '68-70 only (I think). And the big outlet Jeep PS manifold supposed flows just as well as the 340 free flow manifold.

And if you look for a '71-74 DS 340 manifold, they should be cheaper than the '70 down ones as they have a flange for the heat stove and are less desirable and thus cheaper. At least I think the flange started in '71, might be '72.

I understand not wanting headers, but no reason to leave ponies on the table if there is a reasonable option.

 

['Mad Max']

...regarding port sizes and sealing to a magnum head, another bit I can offer into the discussion pool is I just finished firing up my 02 Dakota - it retained its mag 360 and now has an Eddy 7577 and Holley 2bbl Sniper (w/ adapter). To keep things simpler with the exhaust routing and such around the 4x4 oil pan and linkage, I opted for a set of early 70's pre-smog 318/360 center dump truck manifolds (4041466 d-side x2), which so far seal up good (with magnum gaskets). I don't think the ports are quite as big as 340 ports...?...but so far these are sealing up good. These were blasted and Cerakoted - seems to be pretty nice.

 

[Brooks James]

Stay tuned, the magnum exhaust manifolds from a Durango are enroute from HemiEd and I will be heavily documenting their mods and installation on my 70 Dart(orig. /6 with TransDapt /6 to 360 motor mounts). Im hoping there are a lot of guys who will be helped by this. Im sure that I'm not the only one who is interested in inexpensive high flow factory exhaust manifolds that are readily available either new or used that fit with minimum modifications for a fraction of the price of 340 manifolds. I saw an article that 340 manifolds flow only well enough to make 11 more horse power on the dyno than standard v8 manifolds(a body manifolds). Magnum manifolds were designed to have high flow rates. In fact if I'm correct, 92-93 Magnum manifolds have a 2 1/2 outlet and following years have a 2 1/4 outlet.. I MIGHT not be all that far off by saying that magnum manifolds flow almost as well as 340 manifolds

Following years are 1 7/8

 

['Mad Max']

correct, for both the 5.2 and 5.9, which is also the same outlet size as the passenger-side 340 center dump manifold. I just checked and the 318 is 1-3/4" outlet...but a 318 is not a huge engine....

318 above, 340 below -

Still tho...I really wonder how much that tiny difference will 'really' make...

I just found this thread too with some additional info -

318 vs 340 exhaust manifolds

 

[DionR]

correct, for both the 5.2 and 5.9, which is also the same outlet size as the passenger-side 340 center dump manifold. I just checked and the 318 is 1-3/4" outlet...but a 318 is not a huge engine....

318 above, 340 below -

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Still tho...I really wonder how much that tiny difference will 'really' make...

I just found this thread too with some additional info -

318 vs 340 exhaust manifolds

I've never looked at a 318 and 340 log manifold side by side before. Interesting how the 340 manifold is larger, outlet diameter excluded. Makes me think the factory saw value in making it bigger.

 

[RustyRatRod]

Jim Laroy and company did somewhat of a manifold shootout years ago and posted that there is very little IF ANY difference between stone stock manifolds and HP manifolds. As usual, they had the detractors and nonbelievers coming out in droves, but they're the ones with the dyno. If I was worried about ANY kind of performance, I'd be lookin at headers and not futzing around with cast iron paperweights.

 

[DionR]

Jim Laroy and company did somewhat of a manifold shootout years ago and posted that there is very little IF ANY difference between stone stock manifolds and HP manifolds. As usual, they had the detractors and nonbelievers coming out in droves, but they're the ones with the dyno. If I was worried about ANY kind of performance, I'd be lookin at headers and not futzing around with cast iron paperweights.

Do you mean the infamous Mopar Muscle article? Struggling to find a link but the one that showed like 5 or 10 HP difference between the standard manifolds and the HP manifolds?

 

[RustyRatRod]

Do you mean the infamous Mopar Muscle article? Struggling to find a link but the one that showed like 5 or 10 HP difference between the standard manifolds and the HP manifolds?

No. I mean the Jim Laroy private dyno work. It's posted on this site somewhere, but God help you trying to find it. It wasn't in depth. All it was was basically him saying they made really no difference at all. I would trust someone like him FAR further than anyone running a magazine with sponsors.

 

[DionR]

No. I mean the Jim Laroy private dyno work. It's posted on this site somewhere, but God help you trying to find it. It wasn't in depth. All it was was basically him saying they made really no difference at all. I would trust someone like him FAR further than anyone running a magazine with sponsors.

Don't remember that test.

I have issues with the magazine test, not because they could be skewed by sponsors, but because the 300 HP crate motor is too tame to really show a difference. Any motor that get's swapped from the beer barrel intake and EFI to a dual plane with a 4 bbl and sees virtually no difference in power between the two is not going to exercise the 318 manifolds let along anything bigger than that.

I did find a 440 that Jim did (now that I know his screen name) where he put BB HP manifolds on a low compression 440 build and saw almost no power difference when compared to the standard BB manifolds. Is that the one you are referring too?

 

[RustyRatRod]

Don't remember that test.

I have issues with the magazine test, not because they could be skewed by sponsors, but because the 300 HP crate motor is too tame to really show a difference. Any motor that get's swapped from the beer barrel intake and EFI to a dual plane with a 4 bbl and sees virtually no difference in power between the two is not going to exercise the 318 manifolds let along anything bigger than that.

I did find a 440 that Jim did (now that I know his screen name) where he put BB HP manifolds on a low compression 440 build and saw almost no power difference when compared to the standard BB manifolds. Is that the one you are referring too?

It's possible that was it.......but I THOUGH they had done a small block. I may be mistaken, because admittedly, while they have built small blocks, I think their specialty is more toward our larger cousins.