Richard (Tech) will fill in the spaces that I miss and straighten things out, but here's my take on it.

Dual Plane(180 degree)-Divide the V-8 into two four cylinder engines. The V-8 has a firing pulse every 90 degress. The dual plane runners connect the cylinders that fire 180 degrees apart. Two barrels of a four barrel carb feed two cylinders on each side. Therefore, some runners have to pass under other runners, making it have a high and low plenum, which is the open area under the carb. The high plenum feeds the runners that cross over the runners from low plenum. The high side has a fairly easy job of getting the air/fuel to the cylinders because of it's height but the low side has a little difficulty, which in turn, results in a restriction in upper RPM levels. Also, a dual plane halves the amount of carb seen by each cylinder which limits the air/fuel needed in higher RPM levels. The reason they are better for low speed operation is that by splitting the carb/induction into half, the volume to a single cylinder is also half. This results in much less dampening of the intake pulse which leads to a much better booster signal at the carb. That results in a much better fuel atomization at low engine speeds, which means better low end torque and gas milage.

Single Plane (360 degree)-The single plane intake has a common plenum that is shared by all cylinders. This dampens the intake pulse at low engine speeds, resulting in poor fuel atomization. Also, the runners are much larger along with the plenum, therefore dramatically slowing down the velocity in the runners going to the cylinders. On the other hand, once the engine speed is in the upper RPM's, the larger runners, along with the larger plenum volume let's the engine breath all it wants to on the intake side.


High performance street engines are all about compromise. The better of the intakes on the market today that is a true performer of both aspects of this is the design of the Performer RPM Air-Gap manifold. It has high runners and a dip in the divider under the carb.