The Quadrajet is a four-barrel carburetor, made by Rochester General Motors Product Division. His first app was the new 396ci Chevy engine for 1965. His last app was on the Oldsmobile 307 V8 1990 machine, the latter used in Cadillac Brougham and the full-size wagon train made by Chevrolet, Pontiac, Oldsmobile, and Buick. In some areas, especially among the more reputable, Quadrajet is not desirable.
Video Quadrajet
Design
Quadrajet is a carburetor "spread bore"; the primary venturis is much smaller than the secondary venturis. By comparison, carburetors "bore square" have primary and secondary venturis of the same size. Most Quadrajets are capable of a maximum of 750 liters (min)/min (cfm), but some rare Buick and Pontiac models can achieve 800 Â ° c (23,000 liters/minute) for use on high performing machines, and most of 1984 -1987 trucks The pickup also comes with 800-cfm carbohydrates. Most Quadrajets use a vacuum-operated piston to drive the main metering rod to control the air-fuel ratio, allowing the mixture to lean under low load conditions and rich during high load conditions. Less common versions use links that are driven from the primary throttle shaft to mechanically move the power piston. The "E" series (control electronically controlled) Quadrajets series uses solenoid controlled computer controls that respond to electronic signals from throttle positions and oxygen sensors through the computer, ideal for precise fuel measurements and enabling additional fuel under load. The solenoid-controlled metering rod allows the fuel mixture to be very close to the optimum, then the solenoid is the pulse width modulated at about 6 Hz to refine the air-fuel ratio under closed-loop conditions. The electronic version has a throttle position sensor mounted inside the carburetor body, which is driven by an accelerator pump lever.
Quadrajet carburetors have secondary mechanical throttle plates operated by progressive relationships; the introduction opens before the secondaries, and uses the on-demand air valve plate on top of the secondary throttle plate. The air valve is connected by the cam and the connection to the secondary fuel metering rod. As airflow rises through the secondary hole, the air valve is pressed downward, rotating the cam lifting the secondary metering rod. The secondary rod is tapered in the same way as the main metering rod, effectively increasing the size of the fuel gauge when the rod is lifted and providing more fuel. Therefore, the position of the air valve will control the flow of fuel and air through the secondary venturis, even if the secondary throttle plate is fully exposed. Thus Quadrajet acts like a secondary-vacuum carburetor and only delivers more fuel as required.
Maps Quadrajet
Benefits
Significant positive features of Quadrajet are:
- Economy. Unlike most other four-barrel carburetors, Quadrajet has a dramatically different primary and secondary bore. The much smaller introduction acts as a two-barrel carburetor until the accelerator is pressed far enough to begin the secondary opening. The small introduction allows the main throttle plate to be opened wider, and thus makes the carburetor more efficient than the two large barrels, or rectangle bore four barrels.
- Drivability. The small introduction also creates a better throttle response in the throttle application section. Quadrajet has a centrally located buoy that gives it excellent fuel control to form Venturi three, the amplifier.
- Off Road. Quadrajet's float is located very resistant to rate changes caused by cornering or acceleration.
The Quadrajet carburetor is actually a derivative of a variable venturi carburetor called the DOVE (diaphragm operated incoming variable) developed in 1961-63 time frame in Rochester Products. Testing at the GM test facility in Arizona found the percolation problem of the hot engine that caused the difficulty of getting hot due to the flood engine. The DOVE production, which was in progress in 1963 when the heat problem began to be identified, was suspended and the accident project was initiated to fix the problem. Simultaneously the second accident project started to develop a modified DOVE that became Quadrajet. The Quadrajet carburetor prototype is being tested in Rochester Products by Fall of 1963. The hot-start DOVE problem is corrected but not in a timely manner; DOVE production is destroyed and Quadrajet takes its place.
Weakness
Significant negative features of Quadrajet are:
- The leaking fuel bowl. As with almost all carburetors, the Quadrajet bowl has a plug used for closing the remaining holes after fuel drilling during the carburetor making. This plug in the Q-jet sometimes leaking fuel causes the start of a difficult cold engine, erratic idling, poor fuel mileage, and excessive emissions. Many Quadrajets have their fuel bowl plugs sealed with epoxy when rebuilt to prevent leaks. A very small bowl/fuel chamber can lead to fuel hunger in extreme high-performance situations, but can usually be traced to fuel delivery problems to the carburetor, such as a weak fuel pump or rugged eccentric camshaft that pushes lever pump fuel.
- Inlet fuel filters/fuel filters tend to be very fragile. When not careful to align the inserts, it is possible to enter the fuel into cross-thread and removed when tightened in the main house. There are several "fixes" available at post-sale: New, large-sized, self-insertion fuel filters; new fuel filter inserts sealed with O-ring; and Heli-Coil re-threading kit. In almost all cases, the carburetor will require dis-assembly and internal cleaning of the aluminum yarn residue, especially up to and including the needle and seat, (needle valve), to prevent flooding.
- Almost all Quadrajets today have some number of arches from those castings though not too noticeable in so-called "mod Quad" versions after 1974 which are slightly heavier and better designed to withstand arches. The main cause of this arch is the overcrowding of two front carburetor mounting bolts, often combined with basic gasket that does not have hard nylon inserts for bolt holes.
- For many uses, the main throttle steel shaft will tend to use aluminum casting material in the throttle body. This produces a small air leak and in extreme cases, it can cause the primary throttle blades do not close properly. This results in poor idle quality. The after-sales market has responded; some vendors provide repair tools for carburetor bodies, generally in the form of teflon bushings.
- Carburetors have been billed as difficult to set and unreliable by some, however, many times this is only attributed to a lack of knowledge about the unit itself. As a result, many Quadrajets were replaced with other brand carburettors in an often ill-fated attempt to fix problems that were not caused by the carburetor. When tuned properly, Quadrajet is an efficient and effective performance carburetor.
Variant
Major changes to the Quadrajet applied to the 1975 model. The new carburetor is considered "Modified Quadrajets" or "Mod Quads". In addition to the casting revisions that produce larger physical carburetors, the length of the primary metering rod differs from the older '74 and Q-Jets. They are also equipped with an independent choke mechanism that no longer depends on the intake manifold mount choke, and the number "1" is added to the beginning of their identification number. The numbers in the Quadrajet type model show its features. For example, the "E" at the end of the Q-jet model then states that it has an electric choke, "C" represents the hot air style coil element. Delco's original service kit has been sold through GM dealers and Delco distributors and is called "Power Kit". This has long been discontinued, although there are some aftermarket sources that still provide spare parts for this carburetor.
Choke Variants
The provision of chokes for Quadrajet originally in the form of heat-sensitive springs affected by the intake, (divorced divorce), is often referred to as a heat riser. The spring is connected to the rod that drives the choke mechanism on the passenger side of the carburetor, and depends on the intake manifold temperature. Later models, second-generation Quadrajets, (1974-onwards), were designed with self-contained choke housing that held heat-sensitive springs and directly operated the choke mechanism. The system relies on hot air picked up from a small heat exchanger in the intake manifold - and subsequent models, (generally 1978-onward), rely on a 12-volt vehicle system to power heating and spring elements as engine temperatures increase.
The Quadrajet carburetor was also built under a contract by Carter. This is due to the fact that Rochester can not meet the demand for carburetors at various points in their production. Carter-built Quadrajets will have the name "Carter" thrown into it, but are functionally identical to Rochester's built-in equivalents. The "latest" Q-Jets are built for, and sold by Edelbrock. There are several versions created, both for stock replacement and "performance" apps. One version is specifically intended as a carburetor replacement for Carter Thermoquad. The Edelbrock Q-Jets has been discontinued, although Edelbrock currently still supplies some replacement parts.
References
External links
Source of the article : Wikipedia
0 Comments