twin throttle body, quadruple fuel rails, 4 fuel rails,

This twin throttle body with quadruple fuel rails is an example of a Wilson custom intake assembly. This induction range extends to serve Pro Mod engines well as currently used by Brad Personnet and his turbo-equipped Pro Mod Camaro.

By Ben Mozart.
Pictures by Moore Good Ink:

It’s not inconceivable that the induction system of a four-cycle engine just might be its most complicated component.

Keith Wilson made a career of manipulating air flow in racing engines. At 17-years old he was employed at a Florida company called Air Speed Engineering. There he spent ten years porting cylinder heads and intake manifolds. Then in 1985 he branched out on his own and formed Wilson Manifolds. Quickly he seized the opportunity to not only rework cast aluminum intake manifolds but also to explore his theories on cylinder filling in conjunction with induction designs constructed of aluminum sheet metal. As you might expect, these are the fundamentals around which Wilson Manifolds has evolved. Recently we sat down with Keith Wilson to hear his thoughts.

He began by explaining the most basic: the carburetor spacer. Wilson maintains, “Good spacers are the least expensive form of tuning hardware known to the racer.”

open spacer, carburetor spacer

Open spacers for 4150 & 4500-style carburetors or 4-barrel-style throttle bodies are tuning devices that add plenum volume and thus increase top-end power. Good spacers are the least expensive form of tuning hardware known to the racer.

tapered 4-hole spacer, increase CFM, airflow

Where the open spacer increases plenum volume the tapered 4-hole spacer increases CFM. When additional plenum volume is not required, the 4-hole tapered spacer is the more effective of the two—enhancing air flow to the carburetor or throttle body.

shear plate, carburetor spacer, improve downward flow, resist reverse flow

Because the sleeve extensions of the shear plate protrude below the top skin of the racing sheet metal intake, they serve to obstruct reversion pulses. As a result they inhibit the induction charge from returning upward toward the carburetor.

burst panels, wilson manifolds open spacer

Some sanctioning bodies require burst panels for nitrous systems operating with four-barrel carburetors. Since cast intakes are not available with burst panels, Wilson pioneered new safety standards, offering them in their 4150- & 4500-style open spacers.

A spacer attaches to the intake manifold between the carburetor and the mounting pad, or more precisely the top of the manifold plenum. The charge (the fuel and air mixed together) exits the throttle body or the carburetor and flows through the spacer into the manifold plenum. From there it’s distributed to the individual runners and onward to the ports of the cylinder head.

For the best engine performance, the charge distribution in the manifold needs to be even so that each cylinder not only receives the same mixture strength but also uniform 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 cylinder. In simpler terms, it allows the intake manifold and carburetor to work more efficiently.

Four Spacers

Currently there are four distinct styles of spacers on the market each with its own special influence on the intake manifold. An open spacer increases plenum volume, working best in high rpm applications. A four-hole spacer favors low-end torque, designed for lower engine speeds, and has the possibility to aid fuel reversion with increased cam overlap. An adapter spacer is 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.

The fourth spacer, a tapered four-hole spacer, promises large power gains with almost every intake manifold. Where the open spacer increases plenum volume the tapered 4-hole spacer increases CFM (airflow). When additional plenum volume is not required, the tapered spacer is the more effective of the two—enhancing air flow to the carburetor or throttle body. The design of the taper is very intricate and is partially a function of the height of the spacer. It is able to increase air flow through the carburetor because a venturi effect is created at the top of the spacer just below the throttle plates. This causes the carburetor to flow more air through the booster. Then as the air travels through the spacer, the bore is widened to slow the charge down as it prepares to turn toward the manifold runner.

Shear plates are another form of spacer that are attached to the top panel of a sheet metal intake, situated underneath the carburetor. Because the sleeve extensions protrude down through the top panel they serve to obstruct the reversion pulses and therefore, restrain the induction charge from escaping up through the four holes and past the carburetor.

fuel injection assembly, nascar intake

This turbo & blower induction assembly provides smooth air flow transition and succeeds in fully filling the plenum. By adopting D-shape fuel rails fuel flow volume is increased by 50 percent over previous designs.

Dominator bolt patterns, intake elbows

Made for 4150 and 4500 Dominator bolt patterns these elbows are engineered for smooth transition between the components and are sized to accept throttle bodies of 60mm to 123mm.

four-hole throttle body,  four venturii

The first essential of a 4-hole throttle body is to generate abundant airflow. The second is to make them available in a range of sizes to suit all engines. This new 4500-style succeeds in both and weighs 3lbs less than any comparable throttle body.

1-bore throttle body,

Wilson’s single-bore throttle bodies exemplify close attention to the edge profile and the stability of the blade, the rigidity of the joint between blade and shaft, and its smooth operation. Shaft is set in sealed roller bearings for positive axial location.

Wilson’s sheet metal manifolds offer the latest in manifold technology allowing each one to be custom designed exactly for the engine application. In some applications, Wilson pioneered the use of a spring-loaded burst panel on some of his sheet metal intakes. Typically there is one on each flank between the runners with each assembly comprising two plates, an inner and an outer, with an O-ring sandwiched between the plates. If the engine back fires the spring-loaded outer plates open to relieve the pressure and immediately reseal. Especially effect on nitrous oxide applications, it’s just another facet of design that Keith Wilson is famous for.

With the advent of EFI (Electronic Fuel Injection), Wilson has spent a considerable amount of time researching fuel flow through the fuel injectors and into the intake tracts. Each week approximately ten engine builders request Wilson Manifolds to install injector bosses on their intakes.

“It’s a tedious job,” says Keith Wilson, “for the injectors need to be aimed at the intake tract at a precise angle—not just welded in anywhere. If the angle is incorrect and the fuel mist hits a wall, you’ll lose your vapors as they degrade into big droplets and enter the chamber in less than perfect form. This rule is inviolable. No matter if the engine has forced induction or naturally aspirated with a carburetor or fuel injection, if the mixture enters the chamber in big droplets you will lose power.”

spring-loaded burst panel,

Wilson sheet metal intakes pioneered the spring-loaded burst panel. Especially effective in nitrous applications, if the engine back-fires the spring-loaded outer plates open to relieve the pressure and immediately reseal. The shear plates, one shown here on top of the plenum, are especially effective when a substantial amount of nitrous is being sprayed. As the negative pressure in the intake begins to turn toward positive, the shear plates serve to contain most of the nitrous oxide in the manifold, preventing its exodus up and out through the carburetor.

D-rail, D shaped fuel rail

Inside Wilson’s D-rail the injector ports are carefully radiused and the injectors placed in submerged locations. Wilson uses this technique to reduce the harmful effects of siphoning, especially at the injector ports placed at the beginning of the fuel paths. When GM, Pontiac, BMW, and Porsche installed Wilson’s D-rails in their various Daytona Prototype race engines, all—without exception—experienced power gains.

booze racing, red mustang, drag race car, ford fox body mustang

“Wilson is key to our program,” declares Charlie Booze. “My engine builder, Jim Kuntz, was porting his own manifolds, but the process was taking entirely too long. Not only did Wilson’s knowledge and equipment reduce the time taken but also they found more power in the induction system. They are able to do a much better and cleaner job than we can do by hand. I can tell you the advantages of using Wilson from the racer’s perspective; Jim can tell you the advantages of using Wilson from an engine builder’s perspective. Either way Wilson’s service is worth having.”

Keith Wilson & Greg Anderson

Wilson Manifolds has worked closely with leading engine builders and racers for over 25 years. In 2012 Wilson Manifolds celebrated with a couple of NHRA Pro Stock achievements when KB Racing’s Greg Anderson won the Winternationals at Pomona, CA and his team mate Jason Line followed with a victory in Arizona. In Pomona, Anderson raced to his 71st career victory and fifth Winternationals triumph.

Curiously, Wilson uses robust stanchions to mount their fuel rails—3/8in or 7/16in thick—but why so hefty?

“The fuel rails must be solidly attached to the intake manifold,” comments Wilson. “If the pressurized fuel rails fail or become detached from the manifold the leaking fuel pressure on hot headers in a hot engine bay will instantly erupt in explosive fire. A fuel injection conversion kit without correctly installed injector bosses or securely welded fuel rail stanchions is woefully inadequate.”

Regardless of the induction system, only one that is properly designed for the application intended will be the one which will allow the racer the most horsepower gains. Keith Wilson knows that fact and lives it each day.


Nostalgia Lakester equipped with a competition-ported Wilson Manifold, Dominator carburetor, and Wilson tapered 1.5″ 4500 spacer


Bonneville Speedweek 2008 – 1932 Ford Roadster with a 370ci Dodge V8

BonnevilleNostalgia alt2

Team Goldstrom & Jesel with sponsors: Jerico Racing Transmissions, Stef’s Oil Pans, Wilson Manifolds, Victory1 Valves, and Cometic Gaskets

BonnevilleNostalgia alt1

The Lakester ran a top speed of 218.517 in the C/STR class

Wilson Manifolds
4700 NE 11th Ave.
Fort Lauderdale, FL 33334