dual plane divider

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Magster65

Magster65

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I have an air gap rpm and a quickfuel HR 750 for my 408. The buterflies are too close to the center divider on the intake... like they'll rub on it if the carb isn't perfectly centered.
I see conflicting articles on what to do. Right now I think I'm going to machine the center down a 1/2" and run a 1/2" open spacer.
Any better advice out there?
carb n intake.jpg
 
What's camshaft, compression, and cylinder head? I would start, with a 1/2 inch spacer,to start. We kind of need more information, to start with.
 
Abodybomber said:
What's camshaft, compression, and cylinder head? I would start, with a 1/2 inch spacer,to start. We kind of need more information, to start with.
Click to expand...

Details help :)

Cam = Lunati Voodoo 276/284 (234/242 @ .050) and .513/.533
Compression = 10.8 - 1 (zero deck dish piston)
Heads = 6077 Edelbrocks (ported)

Cheers
 
Run the 1/2"..500 spacer....modify as needed. DIE GRINDING,.... Just keep it matching and clean,use,you gaskets..as templates. Ask questions, if needed...brother.
 
Magster65 said:
I have an air gap rpm and a quickfuel HR 750 for my 408. The buterflies are too close to the center divider on the intake... like they'll rub on it if the carb isn't perfectly centered.
I see conflicting articles on what to do. Right now I think I'm going to machine the center down a 1/2" and run a 1/2" open spacer.
Any better advice out there?View attachment 1715100530
Click to expand...
A lot of intakes have a mis aligned carb pad.
If you narrow the offending side of the plenum divder... you're in.
Or a 7/16 spacer would work.
I work the carb flange on every one because of that issue. Most don't notice it with 600 carbs and or running spacers from the get go, wether they need them or not.
 
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so just mill a window on a Performer RPM.....? Easy enough. Did they ever run a 1" spacer on an uncut RPM, that would have taken care of the window milling option, right?
 
pishta said:
so just mill a window on a Performer RPM.....? Easy enough. Did they ever run a 1" spacer on an uncut RPM, that would have taken care of the window milling option, right?
Click to expand...
I agree. I'll round the top corners of the divider and run the open plenum spacer. That should take care of it.
It's a pretty substantial low end gain.
With the divider in place and no spacer I wonder if it messes with the carbs vacuum signal or something?
Thanks
 
E0E2C623-A7C2-4F5E-A4F0-80EB4041AA6F.jpeg
5788C7CF-6EC0-46A9-8AAF-66FD6EA9A076.jpeg
Before and after milling divider with deemel...RPM Air Gap intake... done this on all of my intakes.... it makes a difference... not huge but incremental
 
I sent an airgap back to Summit it was off set drilled so bad. I run a 4 hole 1" spacer after testing a lot of different spacers, 60' times were used vs butt dyno on my stock stroke 340 and 360. The carb tune also changes with spacer style change on my motor, mainly pump shot size and timing.
 
Why only a 1/2"? Magster, looks like you went 3/4"? Why not take the plenum all the way down to the top "floor" of the runners?

What would happen if you removed the entire plenum so the carb opening looked like a single plane opening? One large square hole (with rounded corners).

divider.jpg
 
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69valiant21 said:
Why only a 1/2"? Magster, looks like you went 3/4"? Why not take the plenum all the way down to the top "floor" of the runners?

What would happen if you removed the entire plenum so the carb opening looked like a single plane opening? One large square hole (with rounded corners).

View attachment 1715150271
Click to expand...
The old MP books show this mod for the LD-340. They left some meet in the divider. The divider was milled down to 3/8 of an inch from wall to wall on a front to rear direction. All walls of the divider are rounded.

With the RPM intake, Edelbrock has less of a deep cut. (It’s actually cast in) on the Chevy intake. I would start with a copy of the Chevy dimensions on the center divider milling. Then see how it performs. It is easier to remove than replace the aluminum.
 
rumblefish360 said:
The old MP books show this mod for the LD-340. They left some meet in the divider. The divider was milled down to 3/8 of an inch from wall to wall on a front to rear direction. All walls of the divider are rounded.

With the RPM intake, Edelbrock has less of a deep cut. (It’s actually cast in) on the Chevy intake. I would start with a copy of the Chevy dimensions on the center divider milling. Then see how it performs. It is easier to remove than replace the aluminum.
Click to expand...

I guess I was looking for more of a hypothesis. What do you think would happen? Removing the plenum completely would let the air/fuel mixture flow to the lower side of the intake starving the upper side and leaning out those cylinders? Or it would act more like a single plane than a double plane? Just wondering what you guys think about it, purely hypothetical.
 
69valiant21 said:
Why only a 1/2"? Magster, looks like you went 3/4"? Why not take the plenum all the way down to the top "floor" of the runners?
What would happen if you removed the entire plenum so the carb opening looked like a single plane opening? One large square hole (with rounded corners).
View attachment 1715150271
Click to expand...

I went with what was known to be an improvement... didn't want to 'experiment' with my intake.
 
69valiant21 said:
I guess I was looking for more of a hypothesis. What do you think would happen? Removing the plenum completely would let the air/fuel mixture flow to the lower side of the intake starving the upper side and leaning out those cylinders? Or it would act more like a single plane than a double plane? Just wondering what you guys think about it, purely hypothetical.
Click to expand...
The idea of removing the center divider is to allow the engine to feed off of both sides of the car. The creating of a larger plenum and shortening the runners to what they see helps the dual plane act more in a single plane manor. This is the answer to the rule(s) of,
“You must run a dual plane intake.”
“No carb spacers allowed.”

It is not as effective as running a single plane intake but it does allow you to cheat a bit. I ran this mod on my car and it was very effective for that build.
 
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