Wilson's main business is...
Wilson's main business is reworking cast-aluminum intake manifolds for greatly improved airflow. This led to the creation of the tapered spacer as a way to comple-ment the intake and carburetor.
Individual Runner (IR):
In carbureted form, it's best represented by multiple Webers or similar designs. This manifold is connected to each cylinder separately. It offers a single throttle plate and fuel-metering device per bore, but is usually airflow-limited due to the need to balance velocity throughout a broad rpm range. Another important feature or downfall, depending on the application, is the isolation of the pressure wave pulses from the companion cylinders. Single cylinders provide strong signals at low rpm, so fuel metering at low-to-medium engine speeds is excellent. At high engine speeds, a good single plane will allow the engine to breathe through multiple carburetor bores and is usually a better choice. IR manifolds are expensive and work great in street applications if cost and hood clearance aren't an issue. Some factory-backed, high-end race engines are using a modified IR design configured for EFI that ties the multiple throttle plates together with a common plenum. It's attached above the runners, offering some of the advantages of a single plane when at WOT but isolating the individual cylinder pulses at part throttle.
Tuned:
When an intake manifold is categorized as being tuned, it uses the natural dynamic effects that occur in the cylinder to feed more air into the bore, raising the volumetric efficiency. It actually works under the auspices of dynamic flow effects along with inertia supercharging.
When the intake valve closes, a fast moving high-pressure pulse will hit the valve and bounce back up the runner of that cylinder. By modifying the length and cross section of the runner, the returning pulse can be timed to arrive just when the valve opens for the next event, filling the cylinder with additional charge that is pulled along.
The cam profile needs to open the valve and catch the second pulse or harmonic for it to be effective. This is an OE logic, while some dedicated race manifolds may be designed to work with the third, fourth, or fifth harmonic.
Concerns for valve closing are also expressed. The charge needs to stay trapped in the bore. Since the air column has inertia created by its reversion back from its original collision with the closed valve, it's called "inertia supercharging." When this occurs, the manifold is said to be resonating or tuning. The problem is the manifold and cam profile needs to be matched to this event, and it will only work effectively in a very narrow rpm range. On a normally aspirated engine, the inertia supercharging effect is the only means to increase volumetric efficiency to more than 100 percent.
An advanced computational...
An advanced computational fluid-dynamics computer program was used to model the spacer design before any engine testing was performed.
One of the best examples of tuning is the GM TPI system. It was constructed with an extremely long intake runner of almost 24 inches to the valve seat. It works well to produce high rates of volumetric efficiency at low rpm but was too long to fill the cylinder at high engine speeds, thus limiting horsepower.
Not all manifolds are designed to capture this pulse, with the EFI LT1 GM engine being a good example along with many traditional performance carburetor Pontiac intakes. A short runner is often the hallmark of an untuned manifold, which can be referred to as anti-tuning. A manifold of this style will not offer a definitive point of resonance. This results in lower peak torque but provides more area under the curve with a wider powerband. Most dual-plane intake manifolds are designed to enjoy the benefit of resonance tuning, while the runner configuration and open plenum of a single plane won't apply this theory.
When choosing a cam profile to work with a resonant effect, it has been documented that the intake valve needs to be opened to catch the desired harmonic pulse; any later and the inertia energy is consumed and limits the benefit. This dynamic response in the intake manifold has been studied and defined under different theoretical approaches. Among them are the Helmholtz resonator, ram charging, and organ-pipe theories.