just curious and would like to know what the difference is between a single plane and dual plane intake manifold?

Is there a visable difference?

What type is the stock SB GM manifold?

Not really interested in which brand may be better, just a basic understanding of what the difference is.

Thanks -

 

 

 

There is a very visible difference...the dual plane has a very obvious divider splitting the chamber plenum underneath the carburetor. The stock intake GM provided was a dual plane.

I couldn't even begin to explain the difference as it's like voodoo to me, but I do know that, everything else being equal, a dual plane will give a better idle and low end torque where a single plane will sacrifice some idle quality and low end torque for better performance at higher rpm's.

Let's see if I can 'splain this so I can even understand it. The single plane feeds all cylinders at the same time. If you look down the carb hole (don't anybody get cute with this!!) you can see all eight runners that go to each cylinder. On a dual plane, each side of the carb feeds a specific group of cylinders. Again if you look down the carb hole (never mind you wise guys!) you'll see one side is lower than the other on the primary and secondary ports of the intake. This is how they route the charge to the specific cylinders on a dual plane. The dual plane is mostly a street piece and the single plane is mostly a performance piece.  

Dave

Thanks to you both -

I am just beginning to see how complicated this stuff can become, especially when thinking of updating the upper end of your motor.

If I get the chance, I'll certainly take a peek down that ole carb hole  one of these days and see what you're talking about.

Thanks again -

 

 

Willis7638734.8075578704

The reason for the difference in performance is the length of the intake runners.

The runner length and volume affects the speed of the air in the intake.    When an intake valve closes, the rushing air rams into the back of the intake valve.  This builds higher pressure at the valve.  This in turn caused the air to reverse it's direction and travel back up the intake runner.   This flow creates a greater vacuum at the valve than in the main intake chamber, and the air once again reverses flow and starts back down toward the intake valve.

If the valve open at high rpm with a longer runner, the air is still flowing up the runner.  The intake stroke must stop the flow, reverse it, and then attempt to fill the cylinder.  This is not very efficient, and starves the cylinder for air, reducing power.  

If the valve opens when the air is once again traveling down the runner, it can actually increase the flow into the cylinder, and create a better fill and more engine power.

Short runners require less time, and work at higher rpm.  Longer runners require more time and work best at lower rpm.

A single plane manifold has one large center chamber, and very short intake runners.  In addition to the short runners, the very low restriction of the large center chamber allow less resistance before the runners, and also allows more air at highter speeds and volumes.

A dual plane manifold has two different center chambers.  One side of the carb feeds each chamber.  The left side feeds the outer cylinders on the left side, and the center cylinders on the right side.  This tends to keep the intake runners a more even length than other configurations.  The result is a more balanced flow to all cylinders.  But they are also longer runners than a single plane, which works much better at lower rpms.  Due to the fact the center chambers are smaller, air flow is faster at lower rpm in the chambers.  This helps to atomize the fuel at lower rpm, again making the manifold more efficent at this range.

A single plane does not atomize the fuel as well at low rpm.  The dual plane restricts total flow at high rpms.  In both cases the runner volume and length have a big effect on air flow into the cylinders.

Single plane are more responsive at low speeds.  Dual plane are stronger at top end.   The question is what do you want the car to do.  Most street cruisers and hole shot street cars work best with a dual plane.  Flat out power and drag type operation loves a single plane.

Hope this helps.

 

Welcome back Ken, and thanks for a very detailed answer. You're descriptions are always a pleasure to read, as they are written in a style that us non mechanic types can start to understand. I would love to hang out in your classroom anytime.

Thanks again and I join the others in wishing your wife a big welcome home and a speedy recovery.

 

 

It's good to be back.  And you are very welcome.  Anyone of you who find yourself in Canton OH are welcome to sit in on a class.  That would be fun.

Thanks for the good wishes.  That really helps.

[QUOTE=kstyer]

Single plane are more responsive at low speeds.  Dual plane are stronger at top end.  

[/QUOTE]

Ken, I don't want to question the master, but are you sure you got these two in the right order??  I understood the single plane got best response at high speed with the dual plane at lower speeds.

Larry

Larry, take another look at my explaination.  That is what I said in the body of the of the message. 

But you are right, I did reverse them in the last line.  See what happens when I'm tired?   Sorry to create confusion.  Good catch.  Now if I can just get my fingers to type what I'm thinking........

Sometimes a picture helps.
Here are a couple of sites that might help explain all the text above.

single plane

dual plane