Wilson's experience with airflow...
Wilson's experience with airflow has led to a line of advanced sheetmetal intake manifolds that begin life on a computer screen.
Spacer Theory
A spacer attaches to the intake manifold between the carburetor and the mounting pad. The charge (the fuel and air mixed together) exits the throttle body of the carburetor and flows through the spacer into the mani-fold plenum. There, it's distributed to the individual runners and onto the port of the cylinder head.
For the best engine performance, the charge distribution in the manifold needs to be even so that each cylinder bore not only receives the same mixture strength, but also enjoys a uniform level of volumetric efficiency. If the distribution is uniform but the emulsification of the fuel (the mixing with air) is uneven, performance will suffer. The purpose of any carburetor spacer is to correct the fuel-mixing and charge-distribution issues that are inherent in every intake manifold design. It accomplishes this by manipulating the charge to improve the vaporization of the fuel and steer it more uniformly to every bore. In simpler terms, it allows the intake manifold and carburetor to work more efficiently.
Currently, there are four distinct styles of spacers on the market each with its own influence on the intake manifold. The features of each style are:
Open Spacer:
Increases plenum volume, works best in very high-rpm application, designed for constant rpm and little throttle activity (transition).
Tapered Spacer:
Better throttle response from improved booster signal, improved part throttle charge distribution, greatest improvement is from part to full throttle, may improve carburetor air flow, helps keeps fuel from dropping out due to higher charge velocity.
With no moving parts, the...
With no moving parts, the 1.00-inch tapered spacer produced a 17hp gain on our 455 with a somewhat lean carburetor. Jetting needs to be stepped up approximately six sizes with the Wilson spacer installed.
Four-hole Spacer:
Favors low end torque, designed for lower engine speeds, has the possibility to aid fuel reversion with increased cam overlap (fuel stand off).
Adapter Spacer:
These are used to mate a carburetor to an intake manifold with a different bolt pattern. Traditionally, these spacers impede performance but allow the use of many different carburetors.
Spacers can also be defined by the material from which they're made. They are commonly found in aluminum, wood, and phenolic plastic. The material choice is based on heat-transfer characteristics, machineability, weight, and cost to manufacturer.
Spacer height is usually defined in inches. The common designs are either 1 or 2 inches high. Wilson's tapered spacer is offered in 1.00-, 1.50-, and 2.00-inch heights.
Taller spacers are usually better suited to a higher rpm use. The additional height actually slows the velocity of the charge before it hits the plenum floor and makes the turn into the runner. This may seem contradictory to the desired result of speeding up the flow. It needs to be remembered that charge is both air and fuel mixed together. The charge is heavier than air alone and is more resistant to turning. Additional height from the taller spacer also decreases the radius of the turn the charge needs to make to enter the runner. Think of the plenum and run-ner as a highway with an exit ramp. The gentler the turn, the easier it would be to follow.
A shorter spacer is more effective in low-rpm applications (as was our 455 with peak horsepower at 5,800 rpm) and is often employed when hood clearance is a problem.
The spacer can also be used as a diagnostic aid when questioning if the manifold volume is sufficient for the engine. If a tall spacer is used, it will add volume. If the engine appears to like that, a larger intake tract may be of benefit. In contrast, if the manifold has sufficient or too much volume presently, the taller spacer will produce less power than a shorter one. This was what we found with our Pontiac test engine.