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...musical exhaust manifolds...

1627 Views 45 Replies 15 Participants Last post by  Canadian country boy, 
Mad Max
4
Ok folks - for my mild 360 magnum 'truck' engine...I'm looking at two versions of center dump small block manifolds (for both sides of my engine), and I've narrowed it down to these two: '71 340 p-side, and the later 70's 318/360 truck manifolds.

Both manifolds have similar port sizes, and the same 1-7/8" i.d. exhaust outlet diameter. I was going to use the magnum manifolds that were on the engine, but they aim way way back and frankly make 'getting in there' to access the transmission linkage and such pretty difficult, plus making things pretty toasty and requiring more shields, etc. The magnum manifolds also have the same outlet size of 1-7/8", and with that in mind I'm looking at center dump exhaust manifolds, so back to the 340 or later 318/360 units. The 340's flow good, and I think the 318/360 units probably flow the same, so I doubt there's not much of a flow difference that I would ever notice, and I don't care about gaining/losing 5 hp at 5000 rpm. The later units have more 'cooling fins' and a bigger internal core...but I don't know if that has any bearing.

My brain tells me these (below) both flow about the same, and will flow plenty well enough for my mild 360, again built to be 'done' by 4500 rpm - I'll just be adding gears - not for high rpms - for low rpm grunt work.

So, that said, am I missing something, or would either of these suit me just fine - I'm leaning towards the 340 units...and unless someone convinces me otherwise I'll be picking up a set of the 340 manifolds from a local club buddy tomorrow morning. But if the later truck units would be better...well tell me why.

71 340 -




70's pre-smog small block (318 and 360 I think) -


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Mad Max
...you mean the early 90's Rams (not Jeeps) had the later 'rear-exit' design...but with the larger outlets (2-1/8")? If so I might just go that route. Either way I go it all has to be fabricated...so I'll take advantage of any advantages I can...hence these silly mad discussions :)
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Canadian country boy
I thought you were going with 340 manifolds?!? Those aren't center dump or rear dump, they are in between.....
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Canadian country boy
4
Here are the 340 manifolds.....

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Mad Max
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Canadian country boy said:
I thought you were going with 340 manifolds?!? Those aren't center dump or rear dump, they are in between.....
Click to expand...
...can't do it - bro keep up! 😆 (look at post #19) 🙂

So this is the d-side Dakota manifold compared to my modified d-side 94 Jeep GC manifold -


I went from this (aiming 'at' the starter) -


...to this (now aiming 'forward' of the starter, with plenty of clearance from heat, etc) -


This is the cross-section in case anyone's curious -


What I cannot tell by just 'looking' at it...is the quality of the weld...but maybe you guys that 'know' what quality welding on cast iron is supposed to look like...but it looks pretty dern'd good to me. Unless y'all convince me not to, I'm gonna run this on the d-side, with the respective 2-1/4" mains to the y-pipe...coincidentally the same size as what I had on the 440. Compared to the OE manifolds (and respective 2" main pipes), I don't think 2-1/4" mains would result in any appreciable loss of low-end torque...and most likely will free up some gains in the mid-range -




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Canadian country boy
Don't tell me to "keep up", bro.
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Mad Max
oh don't get all bent - I'd already posted my decision and reasoning not to run the 340 manifolds and I'm not in the mood to repeat things I'd just explained so forgive me for making a quick jib. If the shoes were reversed my response would have been 'doh - my bad 😋- need more coffee! - please carry on...', but that's me. Anyway back to the topic -
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ToxicDoc
Mad Max said:
...you mean the early 90's Rams (not Jeeps) had the later 'rear-exit' design...but with the larger outlets (2-1/8")? If so I might just go that route. Either way I go it all has to be fabricated...so I'll take advantage of any advantages I can...hence these silly mad discussions :)
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Correct. 92-93 had the larger outlets/collectors on the Rams. They were limited run and you can't find a replacement Y-pipe new. You can get a salvage yard item if not rusted or you can fab something. It would be easy if you can get the factory piece.
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Mad Max
ok - I'm still trying to avoid the rear exit, and I'll be fabbing my own y-pipe anyway, so I'm probably going to run my modified GC manifold and enjoy the benefits of both the 2-1/8" outlet and 'middle-ish' dump (y). My only hesitation is running a one-off manifold...with the associated pro's n con's. I'm probably splitting irrelevant hairs but I still tend to split them...
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mttaff
I think going with the new engine setup, the 1off manifold has to be done... have to have some form of your normal voodoo!
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Mad Max
actually...the chess board changes again :p - I just discovered our 94 Grand Cherokee utilizes the LA engine mount locations, with nice big spool-type bushings, which will fit our magnum 360, which means I can go with my 'center dump' plan after all (y) . Ben and I closely examined the 340 and later 70's 360 manifolds, and I'm going with the 360 units - same flow if not more, same fitment, more cooling fins, and more plentiful....at least that's the plan for now :) . I'll probably just try to sell the 340 units ...
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7
My guess would be that any power/torque differences between all these manifold configurations discussed in this thread would only be detected on a dyno & not much noticed from the driver's seat.

I have been tempted to run exhaust straight up through the hood just to avoid all the clearance issues associated with them.

Bucky
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KurtfromLaQuinta
Canadian country boy said:
Don't tell me to "keep up", bro.
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Pay attention. ;D
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Canadian country boy
KurtfromLaQuinta said:
Pay attention. ;D
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Yes well, apparently so 'eh! I hate being called bro.
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SuperBurban
Canadian country boy said:
Yes well, apparently so 'eh! I hate being called bro.
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OHH, I feel the temptation coming on. :D
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Canadian country boy
I know Sam has a bit of a disliking towards me for my free thinking and when I hear that kind of tone I take it as a bit cheeky, but im a big boy, I'll be alright. 😉
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Mad Max
it wasn't intended to be cheeky nor as a 'slight' - just a jib - not even a jab. You're a Mopar brother like the rest of us and it was meant as such, not the 'other' kind of bro, dude (y) :) .

712edf said:
My guess would be that any power/torque differences between all these manifold configurations discussed in this thread would only be detected on a dyno & not much noticed from the driver's seat.
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That is our assessment as well. Yah I know I'm going through a bunch of efforts and time and work and a little bit of money just to find a way to replace a perfectly good set of factory magnum manifolds, but, when the 440 was in there I configured the rest of the local chassis around a 'center dump' exhaust, and if I can find a legit way to retain the same configuration without sacrificing performance or reliability I'll take that detour every time.

Such shenanigans are the origins my call sign - I'll put a maximum effort towards things others would deem a waste of time, or silly, or crazy...but I deem well worth the effort, even if the results are a bust. If there's a better way to build a mouse trap, I'll find it :cool: .
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SuperBurban
Just like headers, the difference will not happen until the engine is winding well above 4000 RPM. Most driving tends to keep the engine around the max torque range.



Font Slope Parallel Screenshot Electronic device
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R!bcracker
KurtfromLaQuinta said:
Pay attention. ;D
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Inflation is to high for me to pay attention
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Mad Max
the manifolds I'm planning to run are the same as what was on the Lil Red Express trucks, and if they were good enough for them they'll be good enough for me :)
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86w250
Isn't debating about stock exhaust manifolds like picking a turd up on the clean end? Just get the damn thing running!
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