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plenum size and why does it matter?

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sdiesel
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plenum size and why does it matter?

Post #1 by sdiesel » Thu Feb 21, 2019 1:16 pm

imagine I were to use a 1 barrel holley sniper style "mixer".
or a carter
or in my case most specifically, a Fish.

but this carb is on a square bore plenum.
like the edelbrock.
or clifford.


or even I have used the Fish on a 360. mopar.

the divided or dual plane plenum interfaces with the carb through altering or directing vacuum signal or wave reverb from valve action?

so when the signal is acting on a single barrel, will the plenum shape be as critical?
maybe more critical due to pressure drop, is there a pressure drop when sucking so much air thru one 2.5 inch hole?
what would be an optimum plenum for a one barrel.beside the obvious solution of one for each cylinder.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #2 by pmuller9 » Thu Feb 21, 2019 5:29 pm

Maybe?
Last edited by pmuller9 on Thu Feb 21, 2019 9:53 pm, edited 1 time in total.

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Re: plenum size and why does it matter?

Post #3 by jason832 » Thu Feb 21, 2019 8:45 pm

I don't think plenum or the volume of the runners matters a terrible amount on the 300 intakes. They aren't as big as a v8 tunnel ram or something.

I've had a 300, stock cam, unheated Clifford intake, headers and 625cfm street demon carb. The primaries are about 1/3 total cfm. So 100cfm each primary barrel. Even high gear below 1000rpm it was SUPER CRISP, heck maybe better than a stock engine. Try opening the big secondaries on my 625cfm carb and its a dog that takes many many hours and a wideband sensor to even make drivable.

I've added carb spacers to clear intake bolt-throttle linkage problems and couldn't tell the difference.

I dont understand the first two paragraphs about a "fish"... Anyways I think the carb sizing is much more crucial than the size of the intake. In my experience the aftermarket ones should do fine even at low speeds when fed properly.

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Re: plenum size and why does it matter?

Post #4 by sdiesel » Fri Feb 22, 2019 12:40 am

the Fish is my favorite go to toy for the inlines. it atomizes so spectacularly, and offers a throttle response like crazy.
it's a 1 barrel, gets me a 15 percent bump in fuel efficiency, and generally rocks.
I tried one on a 360, and fer the sake of Pete it worked.
I dint spin the engine very high as it's in a tonner.
but that little monster even fueled a 360.

I confused myself in original pist. I'm trying to understand the relationship between plenum and barrel sizes,and quantity of barrels.
it's a topic not much discussed,
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #5 by Max_Effort » Fri Feb 22, 2019 6:55 am

jason832 wrote:I dont understand the first two paragraphs about a "fish"... Anyways I think the carb sizing is much more crucial than the size of the intake. In my experience the aftermarket ones should do fine even at low speeds when fed properly.


It's a carburetor designed by John Fish in the mid 1930's.

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Re: plenum size and why does it matter?

Post #6 by arse_sidewards » Fri Feb 22, 2019 7:46 am

Well for starters if your plenum is too big it will take a little bit to go from WOT to a vaccum condition which can result in some interesting up-shifts. :lol:

Ford substantially reduced the volume of the plenum when they revised the EFI intake sometime in the 90s. If making your own intake I would not exceed the volume of the first version of the EFI intake. On a 300 with a carb style manifold I wouldn't worry one bit.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

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Re: plenum size and why does it matter?

Post #7 by sdiesel » Fri Feb 22, 2019 9:48 am

the fish is the mouse that roars.
it feeds fuel through a hollow butterfly shaft 3 hole or 5.
uses 2 psi fuel pressure, needs no heat, as vapor lock is a concern, and will idle way down depending on cam and conditions.
it's fuel savings is a result of almost complete atomization.
the fuel is drawn rather than squirted, matching almost ideally the demand supply ratio.
it does have a genius little acceleration pump.
the 2 inch bore limits airflow to smaller engines,
it's similar to a more modern TBI, concept, but simpler and I believe better.

it lacks a choke, it's prone to heat, and is branded as a 100 mpg fraud carb by some, as there were political machinations involving sanctioning bodies, irs, and what-all.
but darn it , the blommin' thing works like heck!!

my mopar love is beginning to blossom again.them chrysler engineers were impressive, I put one on a 360, and we went to town baby!!!
I did this because the truck needed to be moved and none of the dopey 4 bbl would work right.

for our inlines, I have seen nothing to compare: all things taken into consideration.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #8 by Lazy JW » Fri Feb 22, 2019 2:16 pm

I have been intrigued by the Fish carburetor since I first learned about them as a teenager back in the 70's. I went so far as to contact Mike Brown who at one time had bought some of the equipment and rights to manufacture them (I have no idea if he still does this). He pretty much talked me out of the idea of using one on my White Ox. I need something that will start EVERY TIME at -20° F and not vapor lock at 100° F in the hay fields. My Carter YF does this quite nicely.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: plenum size and why does it matter?

Post #9 by pmuller9 » Fri Feb 22, 2019 2:41 pm

Plenum Size as it pertains to the 300 six in a street application.

There is the average CFM and the peak CFM
The 300 six has relatively large 50 cu in cylinders same as the 400 V8.
During the intake stroke the cylinder gulps that volume from the intake system.
The actual volume depends on the VE so a ported head with a larger cam gulps more volume and the peak CFM is greater.

If the plenum volume is large the cylinder can pull the peak flow from the plenum and the carb only has to supply closer to the average flow.
If the plenum is small then the carb has to supply more of the peak flow and needs to be larger than the carb on the large plenum.
That is one of the reasons why the 300 six can use a much larger carb than expected.
The higher the cylinder count, the closer the peak flow is to the average flow.

However with the large plenum, when the throttle is operating at small openings the air volume flow rate is low and the velocity of the air/fuel charge is low.
The Dual Plane manifold with a multi barrel carb is meant to compensate where the primary path has half of the total plenum volume and the secondary path adds the remaining volume for heavy foot response.

Looking at the Offy and Clifford intakes, the port runners are short and offer very little in the way of low to midrange ram effect for the 300 six and the long common plenum is less than ideal.

I would take advantage of the R&D Ford put into the complete EFI intake manifold.
If there is hood clearance room the Fish Carb could be mounted on top of the EFI plenum or use an elbow to enter the front where the throttle body mounts.
Results:
Equal distribution with total cylinder isolation
Long runner length for low rpm responce
The Fish Carb is away from the hot side of the engine.

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Re: plenum size and why does it matter?

Post #10 by 68Flareside240 » Fri Feb 22, 2019 3:28 pm

Lazy JW wrote:I have been intrigued by the Fish carburetor since I first learned about them as a teenager back in the 70's. I went so far as to contact Mike Brown who at one time had bought some of the equipment and rights to manufacture them (I have no idea if he still does this). He pretty much talked me out of the idea of using one on my White Ox. I need something that will start EVERY TIME at -20° F and not vapor lock at 100° F in the hay fields. My Carter YF does this quite nicely.


I have been really pleased with the YFA on my truck. I know it's not a performance carb, but it's simple, not too much to adjust, and flat out works well with my 240.

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Re: plenum size and why does it matter?

Post #11 by sdiesel » Fri Feb 22, 2019 7:50 pm

paul,
u have genius in you....

a fish with Efi is a terrifying thought.

those little basteurds have wicked throttle response on a ford 1 barrel intake.... imagine efi.
I could even use the dopey little air cleaner they made for that carb.
pure brilliancy ,
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #12 by sdiesel » Fri Feb 22, 2019 8:10 pm

LAZY JW
mike is old now. I got him to answer me one time.glad I had my ducks lined up.
he never manufactored any to my knowledge though there have been efforts.
his book is good but mostly a rehash of known tips collected into one title

it is not a cold weather carb.
it's a race carb principally. (FIREBALL ROBERTS).
ant its great value is its brilliantly simple design with almost perfect atomization .
it will ice, and it will vapor lock. it will blubber like a girl with 4 psi of fuel pressure.
but it will murder most 4 bbl we use on our sixes
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #13 by Max_Effort » Sat Feb 23, 2019 12:47 pm

pmuller9 wrote:
I would take advantage of the R&D Ford put into the complete EFI intake manifold.
If there is hood clearance room the Fish Carb could be mounted on top of the EFI plenum or use an elbow to enter the front where the throttle body mounts.
Results:
Equal distribution with total cylinder isolation
Long runner length for low rpm responce
The Fish Carb is away from the hot side of the engine.


I've seen an 2bbl on top of an EFI plenum.
What worries me is the fuel drop out and puddling. The runner exit is mid plenum and those are long aluminum runners with a somewhat tight 180* curve and other bends.
I'm not saying it won't work but that would be my concern.

I have done a plenum and curved runner intake with about 150* degree runners for a L6. This was due to packaging while having long enough runners for 3rd harmonic. I made this from steel, wanting the heat. This was competition only. It worked fairly well despite not ideal.

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Re: plenum size and why does it matter?

Post #14 by THE FRENCHTOWN FLYER » Sat Feb 23, 2019 1:41 pm

Max_Effort wrote:...
What worries me is the fuel drop out and puddling. The runner exit is mid plenum and those are long aluminum runners with a somewhat tight 180* curve and other bends...

That could be a concern.
In the '60s I ran a SB Chevy 327 with an early TR-1 intake with dual quads. That huge plenum box had runners that extended half way up inside the plenum chamber. Some racers filled the chamber up even with the runner entry so fuel would not puddle into the plenum. I chose to drill a 1/16 pipe thread plug in the lowest part of the plenum with a small hole in it. When I shut the car off fuel would drip out the rear of the plenum, so I knew it was working as designed.

While I'm on here I'd like to comment on the concept of "complete atomization" of the (liquid) gasoline fuel.

You don't necessarily want that.

Fuel vapor takes up tremendously more volume than liquid fuel. And all that volume of gaseous fuel means there is less room for oxygen-bearing air to move through the engine. That spells a less powerful engine. Engines converted to propane or other similar gaseous fuel do not produce as much power as gasoline engines of the same design and one of the (many) reasons for this is how much runner volume is dedicated to transporting the required gaseous fuel to the cylinders. When auto manufacturers moved from CFI to EFI gains were made in efficiency because the runners no longer had to carry fuel through them - only air. The fuel got introduced at the intake port. This is a waaay more complicated scenario than I'm trying to describe here but some of the key points are that one does not want the injector to inject totally atomized, gassified fuel. Injecting smaller liquid particles are better. That way as the injector squirts liquid particles on to the hot intake valve backside there is more room for a denser air charge. The hot intake valve does not instantaneously gassify much of the remaining gasoline particles. Instead much of the atomized gas - which is still in the form of fine liquid fuel droplets - enters the cylinder where - if everything is designed properly in terms of droplet size and proper volume - gets converted into the explosive vapor required for complete combustion, while at the same time the cooling effect of vaporization ensures a denser charge entering the cylinder. Google "Leidenfrost Principal" for more in-depth information.
If you want good efficiency and do not care about producing maximum power for a given amount of gasoline then maybe it would be nice to turn it all into vapor before the flame front reaches it. It is not as straightforward as it seems though. Some liquid fuel entering the cylinders can be a good thing, depending on your objectives.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: plenum size and why does it matter?

Post #15 by arse_sidewards » Sat Feb 23, 2019 2:12 pm

The later revision of the EFI intake (94-ish to 96) has the runners even (or close to it) with the bottom of the plenum so puddling should be mostly a non-issue.

Still, I'd look into a side draft option...
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

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Re: plenum size and why does it matter?

Post #16 by sandboxer » Sat Feb 23, 2019 10:54 pm

THE FRENCHTOWN FLYER wrote:
Max_Effort wrote:...
What worries me is the fuel drop out and puddling. The runner exit is mid plenum and those are long aluminum runners with a somewhat tight 180* curve and other bends...

That could be a concern.
In the '60s I ran a SB Chevy 327 with an early TR-1 intake with dual quads. That huge plenum box had runners that extended half way up inside the plenum chamber. Some racers filled the chamber up even with the runner entry so fuel would not puddle into the plenum. I chose to drill a 1/16 pipe thread plug in the lowest part of the plenum with a small hole in it. When I shut the car off fuel would drip out the rear of the plenum, so I knew it was working as designed.

While I'm on here I'd like to comment on the concept of "complete atomization" of the (liquid) gasoline fuel.

You don't necessarily want that.

Fuel vapor takes up tremendously more volume than liquid fuel. And all that volume of gaseous fuel means there is less room for oxygen-bearing air to move through the engine. That spells a less powerful engine. Engines converted to propane or other similar gaseous fuel do not produce as much power as gasoline engines of the same design and one of the (many) reasons for this is how much runner volume is dedicated to transporting the required gaseous fuel to the cylinders. When auto manufacturers moved from CFI to EFI gains were made in efficiency because the runners no longer had to carry fuel through them - only air. The fuel got introduced at the intake port. This is a waaay more complicated scenario than I'm trying to describe here but some of the key points are that one does not want the injector to inject totally atomized, gassified fuel. Injecting smaller liquid particles are better. That way as the injector squirts liquid particles on to the hot intake valve backside there is more room for a denser air charge. The hot intake valve does not instantaneously gassify much of the remaining gasoline particles. Instead much of the atomized gas - which is still in the form of fine liquid fuel droplets - enters the cylinder where - if everything is designed properly in terms of droplet size and proper volume - gets converted into the explosive vapor required for complete combustion, while at the same time the cooling effect of vaporization ensures a denser charge entering the cylinder. Google "Leidenfrost Principal" for more in-depth information.
If you want good efficiency and do not care about producing maximum power for a given amount of gasoline then maybe it would be nice to turn it all into vapor before the flame front reaches it. It is not as straightforward as it seems though. Some liquid fuel entering the cylinders can be a good thing, depending on your objectives.

Ah, the art beckons. It’s so tough to know exactly what happens, and therein lies the allure of trying things out that don’t originate in a “cookbook”. Thanks FTF for helping keep my grey cells busy:)

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Re: plenum size and why does it matter?

Post #17 by sdiesel » Sun Feb 24, 2019 12:45 am

Thx to all.
FTF, when I plumb propane, the trick is exactly as u describe, hence a positive pressure helps here. But i never added a turbo. To find out.
It would need less than 5 psi to slow gaseous expansion.
I worked for a bit with wolf systems to design a wet injection propane. Easily do able with shelf parts.
Combine with turbo on dry intake manifold, and u git action.
2 problems were not satisfactorily addressed
Knock control
And gaseous expansion as mix entered the chamber under pressure, essentially a/f ratio consistancy. fuel mgmt.
I let it lie after exploratoy investigation.
I had never considered an EfI mani as a wet manifold.
It has drawbacks but all 300c.I. Pulling through that little one barrel, is gonna really play to the Fish strengths. I got a hunch.
But its black art, so really no telling.
I thought of puddling, but since the fish has no chock, the residue might prove usefulon cold start?
I too instinctively considered a reversion tube, kinda like ur 327, but this tube would extend into the plenum from the carb.
I dunno why that came to me but it did.
Im as ignorant as a Mule about this shuttlescut.
But reversion tubes have to do with reverb, and the long tubes may have an effect on the fish, so this tube would be adjustable, for tuning, into the pulses? Shorter or longer by an inch or so?
Thx again fellas for this valuable input.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #18 by pmuller9 » Sun Feb 24, 2019 3:22 pm

No reversion tubes or anything else protruding into the EFI plenum.
The goal with a wet flow plenum is No Dead Zones.

As Max_ Effort is pointed out, the runners enter the plenum off the floor but in addition to that they enter at all different heights.
Modifications would include cutting the plenum top off and raising the floor at an angle with an epoxy or aluminum plate that partially cover the runners then grind a nice transition into the runners.
You would also want 90 degree inserts in the two far corners for smooth flow from the carb to the outer runners.

After looking at what I just wrote I think I would get six long radius 90 degrees elbows and build my own upper intake.

The other thing to look at is to make an adapter plate to rotate the fuel bowl 90* and use the Fish carb as a side draft.

If you find that a single Fish is pulling more than 3 inches of vacuum at WOT and you want more engine power, you might consider setting up a second Fish as a vacuum operated secondary and bring the WOT vacuum down to 1.5 to 2 inches.

Does your Fish carb have an accelerator pump?

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Re: plenum size and why does it matter?

Post #19 by sdiesel » Sun Feb 24, 2019 10:02 pm

Fish, accelerator pump, kinda, it has a sweeper arm that pushes more fuel by pressure into the hollow butterfly shaft.
Itherwise the fuel is drawn by forces of the inlet air.

I dont think it could be a side draft,... But the natural question arises, is there a side draft capable of handling the CFM?, provide performance, and is reliable?
Im in california, but im wasting no time, a gasket awaits me at napa for the throttle body to pattern from.
A plate, an elbow with a 2 bolt exhaust flange makes a one barrel carb mount.
15 seconds on the belt sander to mill the mounting surface, and im ready for whatever lurks behind the bushes of this idea....
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #20 by sdiesel » Sun Feb 24, 2019 10:04 pm

Building an upper plenum is behind my patience, skill, resources, whatever, but continue with ur thoughts. Simeone will fillw tis up with a satisfactory sidedraft intake...
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: plenum size and why does it matter?

Post #21 by pmuller9 » Sun Feb 24, 2019 10:35 pm

This is not for your now but just as an FYI

The main body of a Fish carb will work as a side draft. It is a matter of fuel bowl orientation.

When the ZX Kawasaki and other steep angle port engines came out that were EFI and you wanted to run the engines in a carburetor class, we used Lectron carbs where the fuel bowls were separated from the main body with a custom made adapter allowing the main body to be almost upright while keeping the fuel bowl level.
Opposite change in direction but still relavant in that single circuit carbs don't care about the direction of gravity beyond the fuel bowl.

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Re: plenum size and why does it matter?

Post #22 by 54-4x4 » Wed Feb 27, 2019 1:10 am

Pmuller9,that Lectron carb idea is thinking outside the box.

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Re: plenum size and why does it matter?

Post #23 by 54-4x4 » Wed Feb 27, 2019 1:30 am

Back to plenum size,I thought the larger the plenum the weaker the signal to the carb booster,the smaller the plenum the better the response especially at lower RPM.The bigger plenum should provide more power at higher RPM.I suppose this is relevent to having the correct cam timing and compression etc.
This is something I have been thinking about and I would like to try building an intake manifold.I have never seen a flow bench so I would just be winging it.Any body have any drawings,pictures or ideas on what might the ideal setup?Maybe the Offy and Clifford are already there?

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Re: plenum size and why does it matter?

Post #24 by pmuller9 » Wed Feb 27, 2019 1:05 pm

54-4x4 wrote:Back to plenum size,I thought the larger the plenum the weaker the signal to the carb booster,the smaller the plenum the better the response especially at lower RPM.The bigger plenum should provide more power at higher RPM.

That is what we were saying in post #9 so you are correct.

However runner dimensions and layout are just as important to the application and the Clifford and Offenhauser are just a compromise.
The long equal length runners are a far better match for the 300 for street application.

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Re: plenum size and why does it matter?

Post #25 by THE FRENCHTOWN FLYER » Wed Feb 27, 2019 1:50 pm

54-4x4 wrote:Any body have any drawings,pictures or ideas on what might the ideal setup?Maybe the Offy and Clifford are already there?


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Re: plenum size and why does it matter?

Post #26 by THE FRENCHTOWN FLYER » Wed Feb 27, 2019 2:03 pm

Here's another one I did earlier with longer runners for a lower RPM application and with stub pipes that enables it to be used on either a stock U-flow head or a crossflow head.

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Re: plenum size and why does it matter?

Post #27 by 54-4x4 » Wed Feb 27, 2019 5:02 pm

FTF,you did a nice bit of handy work on those intake manifolds and the headers.

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Re: plenum size and why does it matter?

Post #28 by 54-4x4 » Wed Feb 27, 2019 5:15 pm

The runners on the EFI intake seem very long and thin.Good for bottom end and high velocity.There is restriction near the head port for the injector.I was thinking a 1 1/2 degree taper on the runners but don't know how long it should be for good midrange with a open plenum log type manifold for a 4 barrel carb.

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Re: plenum size and why does it matter?

Post #29 by pmuller9 » Wed Feb 27, 2019 5:38 pm

If you are going to taper the runner you taper the entire runner length.

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Re: plenum size and why does it matter?

Post #30 by 54-4x4 » Wed Feb 27, 2019 6:09 pm

pmuller9 wrote:If you are going to taper the runner you taper the entire runner length.

Yes ,I figured that.It needs a slight taper to increase the charge velocity on it's way to the cylinder head.Just not sure how long the runners should be.
There is probably a relationship of runner length and diameter or volume and plenum volume too,along with the form shape for optimum midrange as in the previous posts.Always with compromises to fit the application or method of manufacture.

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