Technical Fenton Exhaust Manifolds

I picked up a set of Fenton Exhaust Manifolds for my 40 Plymouth project. Looking to get educated. I am thinking that they will clean up nicely. Cast marking is H200-REAR & H201-FRONT.
What are the 2 threaded holes for near the outlets? My thoughts are for intake manifold heat tubes. Also in this picture front manifold outlet is smaller than the rear manifold, 1 1/2" vs 2". What is up with that??

Thanks for the help in advance.
Roger

 

Just a guess, but maybe the 2" was a primary, and the 1-1/2" ran in to it. But that would cancel the dual exhaust benefit.
Regardless, those have to be the hen's teeth of Fentons. Great score!
Bump it up.

 

Could be smaller to get that tube past steering easier? And yes I’d assume they are manifold heat riser holes

 

Any more ideas on these?

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My thought on the smaller outlet is so all the ports flow the same. I would put 2 inch pipes on bolth and not think to hard about it or find someone with a flowbench that can give you the real numbers.

 

Thanks for the input, sleds. I'll give that a whirl.

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The Plymouth/Dodge set isn't that scarce, really - I've had 3 sets including 1 set that were chromed display board items … the Studebaker V8s and Chrysler/DeSoto 6 are tough. The Chryslers may not have ever made it into production.

 

Two of the runners on that back half immediately siamese together into one. Maybe the pulses dump too close together so the joined runner and outlet have to be larger to prevent a bottleneck. I'm guessing it's flow-related (backpressure?) whatever the reason.

 

That's what die grinders are for...

 

I am wondering if firing order has something to do with volume per header or as someone mentioned above, ‘pulses’......I agree there is a reason for the difference.

Ray

 

my dad has a set and they are the same way. Puzzling. Maybe one is designed to fit the stock headpipe, and the other is designed to fit an easily available headpipe from another application?

 

Have seen a few sets on here plus the P15-D24 Forum over the past 10 yrs or so and never had the outlet size difference brought up.......I'm intrigued by it but can't offer any answer, I have seen that Don Langdons Stovebolt Engineering offered a set of cast iron headers which did look very similar to Fentons in the pics tho' I don't remember whether they had "fenton" cast into them.........as for clearing the steering as these were made for a LHD car and the mopar exhaust is on the LHD passenger side thats not an issue, tho' using these on a RHD car doesn't work as they foul the steering column on the front and the pedals on the rear header up to at least the early 50's models.......but they are a neat improvement either way ...........andyd

 

If I remember correctly, the firing order on these is uniform.

These manifolds service 1, 2, and 3 as essentially one bank, and 4, 5, and 6 as the other.

Unless I am wrong, the exhaust pulses alternate banks evenly.

Also, unless I have been smoking my shoelaces, it is not a steering clearance consideration. If memory serves me, the manifolds are on the passenger side.

 

Indeed.

I'd have already clamped that in the mill, and blasted out that hole to full-size.

 

This is what my initial thought was. There does not appear to too much meat at tho outlet tho.

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There have been experiments in the past, in both OEM and aftermarket scenarios, that have attempted to produce "dual torque curves" by manipulating various aspects of engine tune, intake and exhaust manifold runners, plenums, etc.

This may be an artifact of the attempt to broaden a torque curve, by having two different cylinder scavenging profiles.

It's pure speculation on my part, of course.

It might also be that you have two halves, of two different sets, for different displacement engines, in the same family.

 

The only way to know for sure is to put a set on a flow bench or we are all guessing. the only thing I can say is that if there is more than one set like this they where made that way.

 

Hopefully someone, or more than one, has a set or more info and can chime in on this. Hitek, you around??

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Oops, missed this reply earlier. This is a thought...Does he run these ?

 

For what it's worth, this is along the line I was thinking as well.

 

Mopar ran that flat 6 until 1959.....one could thing of a power brake feed for one of the fittings.....

 

No, he has never run them. He picked up the Fenton exhaust, along with an Edmunds head and intake intake back in the mid-70s out of a Chrysler garage in Montana somewhere. He had a 49 Plymouth convert at the time that he was thinking he might put them on it. But then he didn't like the way the heater and the inner fender wells obscured the engine on the 49, he thought they would hide the cool speed parts. So he started thinking he'd get a 48, or else an even earlier car with an open engine compartment. Then he bounced around for years on so many projects that the Mopar flathead 6 dream never came to fruition, now he's too old to do anything. But he still has the stuff. I'm not looking forward to it, but I will end up with it someday.

 

One thing you have to remember about parts like Fenton and Edmonds. they were not designed to be serious race parts. They were designed to sell to the common man for his daily driver. The ability to bolt on the parts without fabrication work was very important. Optimizing everything to the highest standard of performance was not a goal. If that little outlet hole allowed the buyer to use an off-the-shelf head pipe, it would have been a big deal back in the day before everybody had a welder in their home garage.

 

all I know is I would love to hear them .my 50 has a stock manifold split 3-3 and is the best sounding 6 ive ever heard !!

 

When I get my project I will post a video on here for all. I am looking forward to having it completed. Roger

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When they were made it would have been just as easy to make them both the same size. So I'd research the reason before I cut them up. A lot os sixes were thought not to be able to compete with the V8s of the time, probably a misconception. Many were relegated to the lead sled mover job. Sometimes guys played with the sound bu using different sized pipes and different length and type of mufflers.
All that said I really can't figure out why they would have different wise outlets but performance wise sixes don't need huge pipes. So this may be some kind of scavenging that worked on the MOPAR flatheads. The small hole set flows straighter into the collector. The big hole set two come together then flow in at a greater angle and maybe create more turbulence and needs a larger tube there. The design is not sloppiness or a accident.

 

my 41 has 1.5 on one side and 2 in. on the other .did it to get 2 different sounds . sure wont make it fast ! it has 3-3 split headers ,don't sound bad , but fentons sound better on 235