Big droplets of fuel cost you power
From the Editor: The internal aerodynamics of a four cycle engine intake tract are thought to be understood by many people. In reality, very few in the world understand it completely. Keith Wilson has proven himself as one who does understand. What follows is information from the man himself.
Let me start be relating something that everyone understands and has experienced at one time or another: the common cold. Remember a feeling of having to work hard to inhale every breath that was restricted. Of course the cold does go away and it is so much easier to breathe because of less restriction.
The trick is making spacer plates and intake manifolds which allow increased air flow into the engine.
In order for an engine to make more power than before, it must have the ability to refill each cylinder more completely with every intake stroke. As you have already learned, you also must keep the mixture of air with fuel in suspension. The mixture must stay emulsified all the way into the cylinder or big droplets of fuel occur and the engine’s power suffers. This seems to be such an easy thing to say but it is so much harder to accomplish inside the intake tract. Always refer to rule #1: Big droplets of fuel cost you power, period!
Carburetor spacers correct for the application are a cost effective form of tuning hardware. (See Figure 1.)
Carburetor spacer attaches to the intake manifold, between the carburetor and the carburetor mounting pad, more precisely to the top of the intake manifold plenum. The intake charge (the fuel and air mixed together) mixture exits the throttle body of the carburetor and flows through the spacer into the manifold plenum. There it is distributed to the individual runners and on into the ports of the cylinder head.
For the best engine performance, charge distribution in the intake manifold needs to be even so that each of the engines cylinders not only receives the same strength but enjoys a uniform level of volumetric efficiency. If the distribution is uniform but the emulsification of the fuel 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. It simply allows the intake manifold and carburetor to work more efficiently with the spacer in place. Adding the correct spacer can take a bad or ok situation into a very good functioning carburetor and intake solution. With that said, carburetor spacer plates are still best bang for the racer’s buck.
Currently there are four distinct styles of spacers on the market each with its own influence on the intake manifold. An open spacer increases plenum volume, working best in very high rpm applications. (See Figure 1.) 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. (See Figure 2.) 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 to be used on an existing intake manifold.
And finally, we have a new spacer theory that features a tapered bore with the promise of a large power gain with almost every intake manifold. Where the open spacer increases plenum volume, the tapered 4-hole spacer increases CFM (airflow). (See Figure 2.)
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. (See Figure 2.)
Shear plates are another form of spacer that is 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 backwards up through the four holes and past into the carburetor. (See Figure 3.)
Sheet metal intake manifolds allow the very latest in manifold technology to be built in a short amount of time. That allows each intake manifold to be custom designed exactly for the engine application. In some applications the use of a spring-loaded burst panel on some of my sheet metal intakes. Typically there is one on each flank between the runners with each assembly comprising of 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 excessive high pressure and immediately reseal. Especially effective on Nitrous applications, racers quickly realize the benefits that these panels add a safety factor for saving the intake manifold and carburetors from destructive backfires.
Racers using Electronic Fuel Injection (EFI): a considerable amount of time has been spent researching fuel injector flow spray patterns into the intake tract. Every week I get approximately ten engine builders request Wilson Manifolds to install injector bosses in their intakes. This is a tedious job, 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 (refer to Rule #1) and enter the chamber in less than perfect form. Fuel rails must be solidly attached to the intake manifold. A fuel injection conversion kit without correctly installed injector bosses or securely welded fuel rail stanchions is terribly inadequate (see Figure 11).
Keith Wilson has dedicated his working life to airflow or engine internal aerodynamics. At 17-years old, he was employed by a Florida company called Air Speed Engineering. There he spent ten years of his life learning how to improve airflow through cylinder heads and intake manifolds. In 1985 he branched out on his own and formed Wilson Manifolds. Very quickly he seized the opportunity to not only rework cast aluminum intake manifolds, but to explore his theories on cylinder filling. On a clean sheet of paper he designed and constructed of sheet metal his own new style of intake manifold. No longer being limited by the cast intake manifolds produced at that time, it allowed him to apply his knowledge to construct sheet metal intake manifolds with whatever type of port taper, port length, cross-section and plenum volume that he would like. Little did he know that he was about to revolutionize the intake manifold industry. For more information, please contact Keith Wilson at Wilson Manifolds, Fort Lauderdale, FL. Call 954-771-6216 or go online: www.wilsonmanifolds.com.
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