Dual Plane Manifold differences.

Posted By: 68CoronetRT

Dual Plane Manifold differences. - 08/31/11 05:26 PM

I am trying to understand why some intakes have a solid bridge dividing the manifold and others have a "cut away" bridge and yet both are called Dual Plane Manifolds.
Wouldn't the cut away bridge actually defeat the Dual Plane effect? Isn't it more of a Hybrid?

Sorry if this is an elementary question for y'all but I don't get it.

Posted By: Kudakidd

Re: Dual Plane Manifold differences. - 08/31/11 05:41 PM

This is a very old Mopar trick that goes back to the Edelbrock CH4B. I believe the purpose of the notch was to equalize the A/F mixture to each of the 8 cylinders.

Posted By: 1Fast340

Re: Dual Plane Manifold differences. - 08/31/11 06:38 PM

may extend the rpmrange on plenumlimited manifolddesigns thats how i have been looking at it atleast.

Posted By: polyspheric

Re: Dual Plane Manifold differences. - 08/31/11 06:46 PM

The divider notch is for idle quality, and it will be slightly larger for larger engines, etc.
If you open the divider window size (by cutting the divider height down, partially or all the way to the floor level of the upper plenum) top end is improved (by sharing the plenums), but off-idle response and low RPM power will be down. The effects are proportionate to the old vs. new divider window X-area.
Removed completely is inferior to a good single plane manifold since the largest window area is obviously much smaller than the plenum X-section.

Posted By: JohnRR

Re: Dual Plane Manifold differences. - 08/31/11 07:02 PM

Quote:

This is a very old Mopar trick that goes back to the Edelbrock CH4B. I believe the purpose of the notch was to equalize the A/F mixture to each of the 8 cylinders.

Don't forget the then available Holley 3 bbl carb ...

Posted By: 68CoronetRT

Re: Dual Plane Manifold differences. - 08/31/11 10:03 PM

Quote:

The divider notch is for idle quality, and it will be slightly larger for larger engines, etc.
If you open the divider window size (by cutting the divider height down, partially or all the way to the floor level of the upper plenum) top end is improved (by sharing the plenums), but off-idle response and low RPM power will be down. The effects are proportionate to the old vs. new divider window X-area.
Removed completely is inferior to a good single plane manifold since the largest window area is obviously much smaller than the plenum X-section.

Thanks for the replies and taking the time to help me try to get my head around this.

I thought I read that the dual plane intakes provided a better idle and low end response?

Also, is the "true" dual plane set up not really desirable then?

Posted By: Stanton

Re: Dual Plane Manifold differences. - 08/31/11 11:01 PM

The dual-plane is essentially a cross between a single plane and a tunnelram - giving you some of the benefits of each but not the full benefit of either.

Those funky intakes on late model cars are getting the best of both worlds by using a vaccuum control to alternate between the short runners and long runners based on load, rpm, etc..

Posted By: polyspheric

Re: Dual Plane Manifold differences. - 09/01/11 12:37 AM

Read my article:
http://victorylibrary.com/mopar/intake-tech-c.htm#dp

Posted By: BSB67

Re: Dual Plane Manifold differences. - 09/01/11 12:48 AM

Quote:

I am trying to understand why some intakes have a solid bridge dividing the manifold and others have a "cut away" bridge and yet both are called Dual Plane Manifolds.
Wouldn't the cut away bridge actually defeat the Dual Plane effect? Isn't it more of a Hybrid?

Sorry if this is an elementary question for y'all but I don't get it.

I cannot speak to all manifolds over time, or even of recent design, but years ago, most aftermarket dual plane manifolds had a notch at the rear butterflies, which I believe was to accommodate the Holly 3 bbl carb.

On my 508, with considerable dyno testing, I found measurable and repeatable power improvements in playing with the divider on my 2D.

Posted By: fourgearsavoy

Re: Dual Plane Manifold differences. - 09/01/11 02:25 AM

Quote:

Quote:

This is a very old Mopar trick that goes back to the Edelbrock CH4B. I believe the purpose of the notch was to equalize the A/F mixture to each of the 8 cylinders.

Don't forget the then available Holley 3 bbl carb ...

Ding!!! we have a winner
John I thought I was the only one that has set a three barrel carb on an old CH4B to see why they put the notch in there

Gus

Attached picture 6804323-burnoutpicturegus.JPG

Posted By: 68CoronetRT

Re: Dual Plane Manifold differences. - 09/01/11 03:16 PM

Polyspheric,
Thanks for the article link.
BSB67,
When you say "playing with the divider" were you referring to milling a slot into it or closing it up?

Posted By: BSB67

Re: Dual Plane Manifold differences. - 09/02/11 02:05 AM

Opening it up. There was no measurable loss of power from 3000 to 4000 rpm, and started picking up from there.

Posted By: BSB67

Re: Dual Plane Manifold differences. - 09/02/11 02:09 AM

Quote:

Don't forget the then available Holley 3 bbl carb ...

Ooops. Missed that you had already posted this.

Posted By: 68CoronetRT

Re: Dual Plane Manifold differences. - 09/02/11 02:15 AM

That seems to be what I am reading. The gains on the cut away divider are in the higher RPM range.
Well I need to study that article some more. Right now I am planning to stay with a full bridge dual plane and 1" 4 hole phenolic spacer to maintain separation.
Street car so low end to 5500 should be mostly what it will see - unless I miss a gear. LOL Then the rev limiter will/should kick in.