II. PRODUCT DESIGN
The factory intake plenum has 2 major design flaws. The first, and most externally visible, is the fact that it narrows considerably through the center as the round passage from the throttle body side is converted to an oval hole to match up with the lower manifold. Because of this design issue, a ported stock plenum will never be capable of flowing as well as our all new design. The second major issue is the fact that the floor of the factory plenum has an extremely sharp 90 degree turn on the short side of the plenum as air travels through it. This means that the amount of air that can travel through this part of the plenum is greatly reduced, so that most of the air that ends up entering the lower manifold only does so after hitting the back wall and making a sharp and abrupt 90 degree bend directly over the lower manifold opening. Again, porting or modifying the stock plenum will not help this issue either, as the material is already thin in this area and you will still be stuck with the sharp 90 degree turn that the air MUST make to enter the lower manifold.
Our new plenum is an all-new design. By raising the roof and re-contouring the floor, the air makes a nice, smooth sweeping transition over a much longer path before entering the lower manifold. To ensure the absolute best velocity, the core of our plenum (which determines the air path) was designed to maintain a consistent volume from the throttle body opening all the way to the lower manifold. At no point throughout the plenum does the cross sectional area of the plenum get smaller than the openings at either end. This maintains good airflow velocity and smoother flow. The design of this plenum was painstakingly developed with the use of a Superflow Flow Bench to ensure that nothing could be done to improve the flow of the unit. When we tried to change the floor design, we found that the increase in core volume made the airflow turbulent through the plenum and had almost no effect on total flow values. The following is a comparison of the flow values of the stock design and our new plenum.
| Stock Plenum | 466 CFM |
| Stock Plenum 70mm TB | 486 CFM | 4% Increase |
| Ported Plenum 70mm TB* | 530 CFM | 13.7% Increase |
| C&L Plenum 70mm TB | 550 CFM | 18% Increase |
| C&L Plenum 75mm TB | 580 CFM | 24.5% Increase |
| * Source: 06/03 Muscle Mustangs and Fast Fords Magazine |
As you can see by the numbers, unlike the stock plenum, it is the throttle body that restricts the flow on our design. Going from a 65mm throttle body to a 70mm only helps a stock plenum by 20 CFM, but going from a 70mm to a 75mm on the C&L plenum gives you a 30 CFM increase. If the plenum was restricting flow, then going to a larger throttle body would show little to no improvement. This shows that with our new plenum, the maximum amount of airflow allowed into the lower manifold is controlled by the size of the throttle body, and not the plenum itself.
All engines are basically large air pumps. Any flow passage in the total system from the air filter to the exhaust manifold can restrict flow through the rest of the package. Once you reduce these restrictions, or increase the amount of air that can travel through the more restrictive sections of the system, then you will be able to process more air, have a more efficiently running engine and generate more horsepower. With nearly a 25% increase in flow available to the lower manifold of the engine, we knew that we were really on our way to potentially unlocking some power. But it wasn't until the dyno testing (the real measure of a performance part's worth) that we found out exactly how valuable this product will be to the performance enthusiast.
II. PRODUCT DESIGN