72 340 pass side manifold

-
65 Cuda 340 said:
Back in the day - I'm talking sixties, seventies and into the eighties - when 340s were still relatively plentiful and inexpensive, it just made more sense to start with a 340 because it already had the good stuff in it. Whether considering just the motor, or the entire car. Hot Rod Magazine came to that conclusion when it built a 318 Demon project car that ultimately went 12's.

Today is a different world, of course. Not just the scarceness of real 340 cars, or 340 motors, but also the expense of either. Plus, there are so many aftermarket parts you can stuff into a project motor today that provide so much more performance than OEM that the stock equipment is going to be replaced for any high performance build whether starting with a 340 or with a 318. Or even better, a 360.

But I do miss the days when my Dad bought a two year old 71 Duster 340 with less than 20,000 miles for $1750, or when I bought a five year old 73 Duster 340 with 50,000 miles for $1600. I could afford that even on my then meager fresh-out-of-school salary.

(I won't mention the four year old Hemi Charger Dad bought for $1350.)
Click to expand...

I know exactly why a 340 was fast. No secret, but thanks.
 
really good thread - old but very relevant, and I'd like to hop on this 'musical manifolds' train with another manifold question, but regarding 'truck engines'.

I'm building an 02 Magnum 360 - stock long block save for a Comp Cams cam (#20-745-9: 212-218 (264/270), .480/.480, on a 114* LSA), Eddy 7577 intake and Sniper 2300 2bbl. I'm building it for 'off-roading and camping', not racing. The cam will be 'done' at 4500 rpm, and I'm only concerned with low end torque and efficiency - no cares for how well the manifolds will flow above 4500 rpm - I'll just be adding gears.

The nature of my chassis (02 Dakota, about 6000 lbs) hugely appreciates center dump manifolds - much easier to maintain and a ton less heat around critical components than the OE 'rear exit', and a friend of mine has a pair of the '71 p-side 340 manifolds (623s with the 1-7/8" outlets) I can likely get fairly cheap.

My other option is a pair of the 70's era pre-smog truck manifolds (3830684), also with the 1-7/8 outlets. These appear to have bigger 'insides' than the 623s...but not sure these would perform any better than the 623s...for me. The other fine point is there generally seems to be more 'meat' around the mounting bolts with these later 70's manifolds, but the 623s I'm looking at look to have a good amount there (1st pic), and I'm leaning towards the 340 manifolds for my truck.

Interesting note - both sides of the 02 magnum manifolds also have 1-7/8" outlets, just like the 623s and 684s, and I have to believe that...for my 'truck' application...the 623's will flow equally as well as the OE magnum manifolds up to 4500 rpm...maybe even higher, and I gain all of the benefits of the center dump setup that I would very much like to achieve.

I am not concerned about losing 10 hp, but from a low-end torque/efficiency standpoint, can anyone think of any reason(s) the 623s or 684s would be a poor choice? Thanks all

623s (71 340 p-side) - my leading choice for both sides of my 360 -

cQxD5f2.jpg


O4e1YYE.jpg


684s (mid-late 70's truck, pre-smog) - other than 'internal space' and more cooling fins there doesn't appear to be much different from these and the 340 units...? -

Vjepq0S.jpg


KNdbxDf.jpg


02 Magnum 318/360 -

VGliFXI.jpg


zRyCG8E.jpg


- Sam
 
Last edited:
oldkimmer said:
Supposedly the magnum manifolds are the best flowing. Kim
Click to expand...
possibly...but at what rpms? I'm thinking 'any' 318/340/360 manifold likely flows equally enough up to ~4000 rpm to be 'moot' from a performance standpoint, and I've also read they are likely better flowing in the higher rpms...but not by a lot, plus my engine won't be in the higher rpms enough for any flow benefits to be worth the plumbing hassle, so in my case 'better flowing' doesn't always equal 'better'...?

The Jeep Grand Cherokee manifolds have 2-1/8" outlets, but those aren't any better fitting than the other magnum units...s'why I'm looking at these center dumpers.

I'm likely going to use the GC manifolds on a hot magnum 318 going in my 71 Demon...but that's a different story... :)
 
Last edited:
in my mind, a center dump 1-7/8" manifold should flow equally the same as a rear dump 1-7/8" manifold - can't imagine a reason why a rear dump would 'flow' better, but even if it does it can't be a lot better, but either way I've decided to go with the 340 manifolds and call it 'good enough', probably more than good enough.
 
just to follow up - I discovered the motor mounts in our 94 Jeep Grand Cherokee utilize the LA bosses and not the magnum bosses, and as such I'm using two of the p-side GC mounts on my 02 magnum 360 (one on each side), which gives me all the room I need to use center dump manifolds - simple and effective, and all off-the-shelf with a lifetime warranty :thumbsup:

WL3n2pD.jpg


BYFZwGg.jpg


7i9bl8e.jpg


4MQUyPJ.jpg


Also decided to go with a pair of the 3830684 pre-smog manifolds, which IIUC are the same as what the Lil Red Express trucks used, and if they're good enough for them they're good enough for me :thumbsup:
 
turns out the ones I just got are 4041466, which I think is the later 70's manifolds, maybe more correct for an LRE...I think - either way them's the ones I'm using.
 
You must log in or register to reply here.
-

Back
Top