Please school me on intake manifolds

Can someone explain to me the basic idea of WHY certain types of intake manifolds are better for one application than another? Why does a dual plane manifold work better for low end torque than a single plane and vice versa? What difference does runner length, and diameter, and shape, and inner surface texture make in the performance characteristics of a given manifold?

I've seen some very crazy home-built manifolds that boggled my mind(like the 348 Chevy with all the webers at Billetproof) and some from the factory that did the same(Mopar long rams from the early 60's).

I've done some reading, but still don't quite understand how the shape, length, diameter and texture of the tube that brings fuel/air to your motor can make such a huge difference in performance at different RPM ranges...

How about with a turbo, or supercharger? How much does your intake manifold matter once you pressurize it?

Thanks.

 

To start with,longer runners will improve bottom end.And an open plenum manifold is better for max power at higher rpm,because each cylinder can draw through the whole carb;instead of just half on a dual plane.

 

Single plane intake manifolds tend to have lots of plenum area below the carb, and fairly straight runners leading to the intake ports. They also don't use a heat cross-over most times and they normally situate the carb higher above the ports. This all serves to promoted better efficiency at higher rpm levels, but will often cost you a little in low rpm useage due to the lower velocity rates and weaker signal to the carb at off-idle speeds up to about 2500rpm.

Dual plane intake manifolds have longer runners which are curved more and the design is actually two four cylinder manifolds laid on top of each other. In some cases there is a divider beneath the carb which serves to isolate the two planes from each other unless a spacer is used to create a small plenum area below the throttle plates. The dual plane design features a stronger signal to the carb at lower rpm levels, and the flow velocity is higher at those lower levels...giving the engine better efficiency and torque at the expense of high rpm power.

Neither a dedicated low-rise dual plane, or a racing oriented single plane hi-rise intake can provide optimum flow characteristics at both ends of the rpm spectrum, but either design can be worked with to find a better "middle ground" for street/strip engines.

For example, hi-rise dual plane manifolds such as the Edelbrock Performer RPM series feature taller carb heights, straighter runners, and more plenum area to help the dual plane design work well up to a higher rpm limit. Additionally, the Torker 2 series manifolds are single plane intakes with lower carb heights and slightly curved runners to help that design work a little better on street engines that function at lower rpm levels than all out race motors do.

Also, carb spacers can be added to dual plane intakes to gain plenum area, and some manufacturers messed with divider plates in single plane intakes to make them more civil in street applications.

At one time, it was commonly rumored that tunnel rams did not work well on street motors, but recent test have shown that with today's improved cylinder head designs in the aftermarket industry, that these radical intakes can actually make better midrange power than conventional intakes with proper carburetion and tuning! The large plenum areas are tempered by straight runners going downward into the ports, creating a high velocity ram effect which works very well across the normal rpm band.

When you get into supercharged and turbocharged engines, you can often use single plane intake designs to take advantage of their straighter shot into the cylinders, while the pressurized intake charge will serve to insure that velocity is adequate enough to provide low speed performance as well.

You could spend years researching the aspects of performance intake manifold design, but these are the very basic principles to help you understand it a little better. (I hope!)

In short, dual plane manifolds = higher velocity and a stronger signal to the carb

and...

Single plane manifolds = lower velocity and weaker signal at lower rpm levels.

Each has it's place, but like I said, there are ways to help either design work better on a dual purpose machine that sees both drag strip AND street duty!