In all the years that I have been messing with Mopars, I always wondered something and I have never seen a post on it.
If you look at the HP 383/440 exhaust manifolds, there is really a huge difference between the drivers side and the passenger side. No kidding? right! The drivers side looks like it ought to be a great flowing manifold, while the passenger side looks to be much more restrictive. I have no idea how to do a flow test, nor do I have the equipment, but I have to wonder, with all the technology that is available, and with so much research done by the F.A.S.T racers, if anyone ever tested and got numbers that show whether they flowed close or if they had a large disparity.
Anybody know?

I don't know.

But, relative to the topic anyway......here is a link that may be of interest...the first two charts posted are a comparison between low perf and high perf stock exhaust manifolds...

https://www.forabodiesonly.com/mopar/threads/dyno-testing-a-stock-1972-440.249866/

the low performance/std manifolds being "more equal" to one another doesn't seem to make a lot of difference in this application, anyway.

Yeah Zippy, I read that the other day and it got me to thinking about it. I am not disputing their findings, but it seems hard to believe that Ma Mopar would have spent all that money on developing HP manifolds for a lousy 6-8 horsepower, but stranger things have happened! I was finishing up a 440 build and getting it ready to break in on a friends engine stand, and was having trouble with the drivers side manifold hitting the fabricated valve covers high up, not so on the passenger side which does not swoop up high. Anyway, that reminded me that I always wondered how much difference in flow their might be between sides and how that would affect performance. If I had a dyno, I'd be dangerous, as I would see if I could reverse mount a drivers side manifold on the pass side and see if it made a difference. Kind of on the subject of manifolds, I remember reading an article in the 70's about how when testing a new LS 6 454, they picked up almost 100 hp using headers vs the restrictive factory manifolds. I always thought that that Chrysler was way ahead of the others in both exhaust and intake manifold design. I wonder if any of the engineers that did that development are still around to ask, I bet that would be interesting!

They didn't have computer simulation in those days nor did they have computer design tools so they just had to carve it out of wood and then have it cast. Most of the design would have been "what fits", "what does it cost", and "how does it look". How it actually functioned would've come in third or forth on the list.

Having said that the HP manifolds actually work pretty well. I've run them for years on my cars and my B body makes enough RWHP to scare most people. If you're willing to spend money elsewhere you can run 10's in a B body car with exhaust manifolds hooked to a full exhaust system so they work okay.

Interesting results. Thanks for sharing that link Zippy.

A friend of mine who is a board member here and a former Chrysler tech from back in the day told me when I was de-tuning my 440-6 from a header high compression motor to a more pump gas friendly manifold to more stock motor that Chrysler was pretty advanced as far as exhaust manifold/engine breathing was for the big 3...another friend who was involved with the cars directly as delivered and being set up for tuning for the magazine articles told me the same...as far as street driving and throttle response, I think I feel a little more torque seat of the pants wise...not top end or time wise obviously as a street car I’ll never know...but I think mother had her thinking cap on when exhaust development was in full circle starting with the maxies and ability to uncork the pipes...

Pontiac did pretty well with it's Ram Air/HO intakes and long branch exhausts
also. Maybe some of the same engineers?

I'm sure the factory engineers tried their best to create good exhaust manifolds but they didn't have the tools 50 years ago to really solve the problem. If you look at modern exhaust manifolds such as the ones on the LS engines you'll find out that they give up nothing to headers. There are been a fair number of dyno tests that show no improvement from headers on stock LS powered Corvette. So the engineering has come a long way in 50 years.

IMO, this falls right into the “it depends” category.

The test in the link has the hp manifolds making 4hp over the logs(272 vs 276), and 3 step headers making 15hp(272 vs 287)over the logs.

A member posted some numbers from his TF/6bbl topped stroker a couple months ago where the manifolds cost the motor 90hp.

My suspicion is that on something a like a 600+hp 500”+ FAST type build(as opposed to a 275hp <8:1 440) there would be more than a 4hp difference between the HP pieces and the logs....... but having not done that test myself, I can’t say for sure.

I'd have thought by now that someone would've tested a pair on a flowbench to at least get a number. Maybe even a comparison between stock and extrude-honed.

I guess you could put it on a flow bench and get some comparative numbers. But what the exhaust does is so much different than an intake, and what is important is different. How and what makes the exhaust help the intake (I.e. the only part that makes power) is different. The exhaust is under hundreds psi positive pressure pushing the exhaust out, verses 13 psi of vacuum.

I wouldnt be surprised if a manifold port flows about as good as a 1 3/4" header tube, but clearly the long tube header helps the intake a lot more and will make a bunch more power.

Sure, exhaust is very different from intake vacuum. I just wonder how the different ports compare in CFM when they all neck into the exit, what the quality of their flow is, what the total/exit max CFM might be.
I like AndyF's manifold deal with the 3" headpipes, and the notion of stock-appearing parts in general.
I just think it'd be nice to have some math to set up a combination for manifolds, but maybe I'm over-thinking it.

For what it's worth, I switched from a 1 7/8" Hooker comp long tubes, 2.5" compression bent exhaust with Flow Masters to HP manifolds, TTI mandrel bent 2.5" exhaust with Dynomax Super Turbos and lost .23 in the 1/4 mile. Both days were similar weather conditions but, the track was not as good on the HP manifold test day. If a complete apples to apples comparison was done on the same day, I would say I could have gotten the difference down to .15 or there about.

Andy makes the point that they did not have sophisticated computer modeling then, but they did have dyno's and I am sure that they must have used them to confirm the improvements as they developed the HP manifolds. Like I said, no way Ma spent big bucks and got a couple of hp. If that were the case, they would have canceled the project and stuck with the old log style manifolds. I sure would like to see the results of their testing and would like to know the flow difference between the sides. You have to wonder, say the pass side flows 10-15% less than the drivers side, what would the effect on performance be besides the obvious restriction, would'nt it also cause reversion and mixture contamination?