Thoughts On Fuel Distribution Dams (Intake Manifold)

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12many

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The MP Engine Book mentions installing distribution dams in many single planes. As an example, for the M1 single plane intake it is recommended to install two dams, in front of the #4 and #5 runners, 3/8” high. It is stated “when used with stock cylinder heads” as well as “engine is able to make 5-7 horsepower more” Regardless of how much hp would/wouldn’t be realized, how does this modification apply to better aftermarket (or even ported oem) cylinder heads? In general, does the mod still apply for better flowing heads? Would there be any noticeable gains or improvements, and is it still worthwhile to do for a “strip/street” application? I’m of the mindset of “I’ll never notice the difference and is best left to the competitive racer” or possibly needed after doing plugs readings otherwise no need? Thoughts from those who have experience with these recommendations (for any single plane) or in general when using heads other than factory welcome :)

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I think there are other ways to address distribution issues. You can never stop wet flow, but you can reduce it. Reducing wet flow cleans up a bunch of distribution issues. That’s one reason why guys have issues with cold intakes. They don’t atomize the fuel like a heated intake, so you have to account for that.
 
yellow rose said:
I think there are other ways to address distribution issues. You can never stop wet flow, but you can reduce it. Reducing wet flow cleans up a bunch of distribution issues. That’s one reason why guys have issues with cold intakes. They don’t atomize the fuel like a heated intake, so you have to account for that.
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I think your approach to hackin up the intake ports with that rough portin helps. Hackin. LOL
 
RustyRatRod said:
I think your approach to hackin up the intake ports with that rough portin helps. Hackin. LOL
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LOL...that and a correctly sized carb with a properly designed booster will do wonders to clean up some of that stuff.

Im still learning on the booster stuff. Without a flow bench right here, it’s a PITA ago test anything. Should have kept my flow bench. Just a bone head move on my part.
 
yellow rose said:
LOL...that and a correctly sized carb with a properly designed booster will do wonders to clean up some of that stuff.

Im still learning on the booster stuff. Without a flow bench right here, it’s a PITA ago test anything. Should have kept my flow bench. Just a bone head move on my part.
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Then buy you one dummy.
 
Of all the single planes guys here are using, many showing their porting work and plenum modifications, Ive yet to see any with dams. So knowing that one can only assume this is an old trick used back in the day and as YR mentioned there are other ways. Nothing I’m doing in the foreseeable future only a curiosity
 
12many said:
Of all the single planes guys here are using, many showing their porting work and plenum modifications, Ive yet to see any with dams. So knowing that one can only assume this is an old trick used back in the day and as YR mentioned there are other ways. Nothing I’m doing in the foreseeable future only a curiosity
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Yours is the one with the epoxy to re-form the plenum into a regular square bore, isn't it, from another thread?
I wonder if that helps some of the distribution issues in the base casting, making the Mopar air dams less necessary? Maybe that is one of the ways yellow rose was mentioning can help take care of it?
 
On my sb416 stroker, it has what the builder called a "Turtle".
It appears to direct fuel towards the cylinders.
Has anybody else heard of or used one of these?
I have a picture, I will have to find it.
 
This? interesting
th?id=OIP.jpg
th?id=OIP.jpg

“Turtles” are cast aluminum manifold inserts designed by Jean Dittmer and manufactured by BRODIX®. These inserts fit in the bottom of an intake manifold to direct the flow of air and fuel mixture to increase horsepower, torque, and driveability.
 
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Bobzilla said:
Yours is the one with the epoxy to re-form the plenum into a regular square bore, isn't it, from another thread?
I wonder if that helps some of the distribution issues in the base casting, making the Mopar air dams less necessary? Maybe that is one of the ways yellow rose was mentioning can help take care of it?
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That is one big fix and 12many did a bang up job on his. Some of the distribution issues with the SD is directly related to the flange. That’s why I always weld them up and make them correct.

The first time I did it I found 12 average HP and IIRC it was 15 better at peak HP.

I am also playing with anti-reversion/shear plates as I think any time you can dampen reversion and shear the fuel better, you can run less fuel through the intake system, and less fuel in the system to begin with is always a better idea.
 
There's a reason why carbs for oem intakes have booster tangs and that's to improve distribution. From memory one study showed a 7 point afr spread between the highest to lowest cylinders.

Here's a study where they separated wall film (fuel deposited on the walls) and the mixture that makes it to the cylinders:

An Investigation of the Liquid Petrol Wall Film in the Manifold of a Carburetted Spark Ignition Engine: Effect of Carburettor and Manifold Geometry on Wall Film Quantities, Engine Performance and Emissions | Semantic Scholar

Here's what they found:

"Removal of the wall film yields a significant reduction in the emission of unburned hydrocarbons and virtually eliminates cycle-to-cycle variations of pressure in the engine cylinder."

Now think about what happens when one cylinder fires at 10-1 and another fires at 17-1? How long does it take for the cylinder to recover from a lean or rich miss fire?

Lots to think about.
 
12many said:
The MP Engine Book mentions installing distribution dams in many single planes. As an example, for the M1 single plane intake it is recommended to install two dams, in front of the #4 and #5 runners, 3/8” high. It is stated “when used with stock cylinder heads” as well as “engine is able to make 5-7 horsepower more” Regardless of how much hp would/wouldn’t be realized, how does this modification apply to better aftermarket (or even ported oem) cylinder heads? In general, does the mod still apply for better flowing heads? Would there be any noticeable gains or improvements, and is it still worthwhile to do for a “strip/street” application? I’m of the mindset of “I’ll never notice the difference and is best left to the competitive racer” or possibly needed after doing plugs readings otherwise no need? Thoughts from those who have experience with these recommendations (for any single plane) or in general when using heads other than factory welcome :)

View attachment 1715691725

View attachment 1715691726
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Lookin at that diagram, it would appear they have the dams there to help slown down the smaller radius runners so they would be about the same speed as the larger radius runners. So why not on all four smaller radius runners? Maybe my thinkin is wrong. lol
 
Bobzilla said:
Yours is the one with the epoxy to re-form the plenum into a regular square bore, isn't it, from another thread?
I wonder if that helps some of the distribution issues in the base casting, making the Mopar air dams less necessary? Maybe that is one of the ways yellow rose was mentioning can help take care of it?
Click to expand...
Yes, as have quite a few others. I never ran it as cast, but when I do get my motor buttoned up and going I will only know that that part of the intake has been optimized (based on the info gleaned here) but will not have any before to compare to the after which I prefer having with most of what I do. The turtle looks interesting, and shear plates as well, likely would render “dams” an obsolete practice maybe?
 
RustyRatRod said:
Lookin at that diagram, it would appear they have the dams there to help slown down the smaller radius runners so they would be about the same speed as the larger radius runners. So why not on all four smaller radius runners? Maybe my thinkin is wrong. lol
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My uneducated guess would be maybe it’s the way the order of intake draw of each cylinder happens, how the mixture is drawn which just causes those two runners to need them?? No idea really! Someone here knows for sure
 
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The first issue is you can not predict how the air and fuel act in the intake manifold. No one can, but! There are patterns that come and go. To this end.....

The intake has the runners cast as close as the engineers idea as possible since it was on a sheet of paper first and then cast second in holes it acts or performs as they hope it will.....

The stock runners need the dams to help balance out the mixtures. Be it for the dam to slow down or (IMO, more correctly) speed up the charge through a smaller orifice, to help every thing come into balance or closer to it.

As far as a mod to a stock head.... vs a ported one....
This is a question I also asked myself. Once ported, equally.... which is not 100% possible port to port, this mod could still be useful. But how do the flow rates of each cylinder head port compare to each other and to the stock head vs ported head may hold the key.

I have never seen anyone list a port to port flow test.
I have never seen anyone list a intake manifolds flow rate runner to runner. Or more importantly the intake on the head!
Ported or stock for intake or head.
Once you have this done, then you can see what cylinders from the intake to the valve are going to be strong or weak. From there, truly, from there and only there can you make a call to what can be done.

Since none of us has the equipment time or money to do this, (maybe a member or two?) the only way your going to figure out what works and doesn’t is to track test.
 
56DBFC0B-BA4D-4C2C-9EB0-6120184686D6.jpeg
So.......when would you put a Turtle in the plenum? Always if possible? A “it can’t hurt” item or only in certain applications? Any thoughts?
 
A56 said:
This? interesting
View attachment 1715691814View attachment 1715691815
“Turtles” are cast aluminum manifold inserts designed by Jean Dittmer and manufactured by BRODIX®. These inserts fit in the bottom of an intake manifold to direct the flow of air and fuel mixture to increase horsepower, torque, and driveability.
Click to expand...
Looks like someone stuck a flower in there and painted it aluminum lol
 
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