About the Book

• The Lady and the Unicorn: A Psychological Metaphor



• Dreaming�With Eyes Wide Open: Schizophrenic Hallucinations



• Information Processing in Schizophrenia



• Clarification of our Clinical versus Forensic Function: Dual Relationship



• Art Psychotherapy



• Lord of the Rings: A Psychological Metaphor



• Aviation Psychology



• So, You have just been Passed by a Girl! A Holley Carborator may help



• Approaches in Memory Rehabilitation



• Memory Enhancement Module



• Negaunee Center



• The Final Transition



• Is Deinstitution- alzation a Misnomer



• Token System: a Psychiatric Case Study



• A Token Economy System: Inpatient Psychiatric Population



• Insight: An Aspect of Neurocognition

Although, we cannot afford to drive it now, we can still talk about the Holley Carburetor.

I guess this is one of the best practical applications of both air and fluid dynamic physics, which will actual put you in the mix. I have recently finished installing the Holley on an old Chevy V-8 and used the Haynes manual as a guide. I thought it would be helpful to others if I tried an offer you a brief summary of the basic fundamentals of this type of carburetor. You already know a carburetor mixes gasoline and air into a combustible mixture. The carburetor senses the speed of air and atomizes the proper ratio of fuel into the airstream. Dumping fuel into the carburetor is eloquently done by the principal of pressure differential. Through moving fluid from a high pressure towards a low-pressure area. For example, this is demonstrated by drinking a soda with a straw. The atmospheric pressure bearing down and the soda, which is a constant 14.7 pounds per square inch. When drawing on the straw the atmospheric pressure in your mouth has a much lower pressure thus, the liquid is forced up through the straw. This same pressure differential is what the idle and main circuits use to push gasoline out of the carburetor float bowl. It is dispersed into the airstream moving through the venturi. The intake and exhaust valves and the pistons work together to create an air pump forming a manifold vacuum. The venturi effect creates a pressure difference. Imagine a straight tube with air flowing through the speed of the air is constant, but if we pinch this tube slightly, the air flow is restricted and the air molecules must speed up to pass by this restriction. This venturi effect was named after an Italian physicist (1746-1822) whose law is �If gas velocity increases, gas pressure decreases.�

There are seven cleverly designed circuits in a standard Holley Carburetor. The first, fuel inlet system or float circuit. Second, idling. Third, transfer off-idle, fourth, main metering, fifth power, sixth, accelerator pump and finally the choke circuit. The float bowl is really a fuel reservoir. In a four barrel Holley the primary are open and the secondary barrels blow open only when slightly more power is necessary. The float bowl must maintain a specific level of fuel at all times whether accelerating, decelerating or turning. Thus, as the fuel fills the bowl it lifts a float. As the pressure rises, a needle presses against or seals the seat so that no more fuel can get in. The bowl vent provides an air passage and depressurizes the fuel being pumped to the float bowl. The vent is located in the center of the bowl but high enough to prevent fuel spilling out during hard cornering. The float is usually made of nitro close material, which never leaks and provides constant buoyancy. Every Holley Carburetor has a specific factory adjusted float setting, which closes the inlet valve. The height of this float setting is high enough to provide fuel to all circuits during fast starts and high speed cornering. Yet not so high that fuel is spilt when driven or parked on an 18-degree slope or 32-percent grade. Center-pivot float are best designed for high-speed cornering because it is not as effected by centrifugal force. Where as side mounted floats are better for accelerations and heavy braking conditions. Most Holley inlet-valve needles are viton-tipped to resist dirt and seat even at low closing pressure ranges. The seat diameter and orifice length determine the fuel flow within certain pressures. The seat size (S-.130) must be larger enough to fill the bowl quickly for acceleration after a hot-soak period (sitting parked with a hot engine) and extended wide open throttle operations at high RPM.

Obviously a cold start posed a formidable problem for any carburetor but solved by the choke system. The choke plate when closed provides an important high vacuum below the plate. The air/fuel mixture is adequate for warm engine idling but not a sufficient vacuum with a cold engine. Thus, a secondary plate known as the main nozzle blocks off the airhorn and enriches the mixture. The enriched fuel mixture is necessary due to low manifold pressure, the puddling through recondensation on carburetor surfaces, the fuel is cold and less volatile, the main metering system at this point is more liquid then vapor secondary to the low air velocity available to atomize it. During starting, only a small portion of the fuel is vaporized enough to burn effectively. The vacuum break diaphragm is a thermostatic bimetal spring that holds the choke plate closed until the engine warm up. Sometimes depending on the ambient temperature a rich mixture is not sufficient to keep the engine running. Higher idle speed is needed to compensate for the friction of cold parts rubbing together. Thus, a fast idle cam is used. Before starting a cold engine press the throttle all the way to the floor and release it, this will allow the choke to close and position the throttle plate in a partially open position. The fast idle cam is set to 800 to 1100 RPM on a cold engine. If you absent-mindly pump the throttle several time without pushing it to the floor you could simply flood the engine.

The idle and low speed circuit requires a richer mixture at idle then a partial throttle operations. The carburetor delivers fuel into the airstream and the difference in pressure between the float bowl, which is vented to the atmosphere, and the relative vacuum below the throttle plate is the basis of this circuit. The lower level of the idle tube has a calibrated hole in it called a jet. Outside air is introduced into the idle circuit through the idle air bleed tube. This is where the air fuel emulsion is trimmed and leaned out through the channel restriction. The curb-idle port and mixture adjustment screw controls the amount of mixture, which can flow through the idle port and determines the strength of pressure differential exposed to the throttle plate. Sometime the needle and/or the size of the jet can be adjusted thus solving the hesitation you experience when you floor the throttle. Turning it clockwise you obtain a leaner mixture. The idle transfer port helps in making the transition form curb idle to cruising speed. The port itself is slightly above the throttle plate and bleeds the mixture making it leaner and improves its ability to atomized the fuel. The throttle plate is located at the base of the carburetor and is self closing. It controls engine speed and power by changing the density not the volume of air to the engine. If the venturi is too small, top-end horsepower is reduced. High performance carburetors have a small primary venturi with a bigger secondary venturi for better top end flow. For big carburetors they need a higher engine speed to activate the main system. Fuel for the main meter circuit is stored the main mixing chamber. The main jet determines the amount of fuel. The size and shape of the hole of the jet is given of a specific pressure difference numbers an engraved on any particular jet such as 48 or 55. Although suction alone does not proved a means of converting liquid gasoline into a spray mist. Atomization occurs when a stream of liquid is placed within a fast moving column of airs. But the gasoline droplets are still too large to be atomized for combustion. The discharge nozzle makes the emulsion light, frothy mixture of fuel and air using the main air bleeder. Similarly, to finishing a cold drink with a straw some air is sucked up with the remaining soda. The emulsion tube is a small brass tube with tiny holes in it for better atomization. The fuel flow increases and the main jet restricts the flow as the main well drops below the calibrated float bowl level. The main well air bleed flows through perforation in the mixing tube. The air in the emulsion tube bubbles out through the tiny holes forming an emulsion ready to burn. The tube from the main mixing well to the venturi is the main nozzle. As the air velocity in the venturi reaches a point it produces a vacuum to create a difference in pressure between the nozzle tip and the vented port to the atmosphere beginning it travel from the fuel well to the venturi. Holley carburetors also use a booster venturi to distribute the mixture more evenly around the throttle bore. Ideally, manufactures want a 20-degree entry angle and a 7 to 11 degree diverging angle below the vena contracta. But this tall structure would not fix under the hood. The booster venturi allows a much shorter main venturi so the carburetor to at least fit under the hood.

The power circuit provides extra power for acceleration or passing. The manifold vacuum is a good indicator of load. Vacuum is stronger at idle and weaker at open throttle. As you open the throttle plate and manifold vacuum drops there is less restriction of air flowing through the carburetor. At idle the manifold vacuum hold the diaphragm closed against the pressure spring. Without a strong vacuum signal fuel cannot flow smoothly, the engine hesitates or stumbles on the lean mixture. The accelerator pump compensates for this effect. This pump squirts a pressurized burst of raw fuel into the carburetor above the venturi. The mechanically actuated accelerator pump is directly linked to the throttle and gives one squirt of fuel aimed at the booster each time the throttle is opened quickly. These represent the basic principles of the Holley Carburetor so now you are good to go. Clearly, one can see that the carburetor is mechanically engineered to provide you with high quality performance under all driving condition. The Holley is especially designed and easily adjusted for making specific modification on the racetrack you are running.

Reference