In automobile mechanics, the Quadrajet is a four barrel carburetor made by the RochesterProducts Division of GM that was widely used in General Motors motor vehicles until 1990. Its first application was the new-for-1965 Chevy 396ci engine. Its last application was on the Oldsmobile 307 V8 engine, which was last used in the Cadillac Brougham and full size station wagons made by Chevrolet, Pontiac, Oldsmobile, and Buick. Contents [hide] 1 Design 2 Advantages 3 Drawbacks 4 Variants 5 References 6 External links Design[edit] The Quadrajet is a "spread bore" carburetor; the primary venturis are much smaller than the secondary venturis. By comparison, a "square bore" carburetor has primary and secondary venturis of similar if not exactly the same size. Most Quadrajets were capable of 750 cu ft (21,000 l)/min (cfm) maximum, but some rare Buick and Pontiac models[1] were capable of 800 cu ft (23,000 l)/min for use on high performance engines, and most 84-87 pickup trucks were also equipped with the 800Cfm carb. Most Quadrajets use a vacuum operated piston to move the primary metering rods to control the air-fuel ratio, allowing the mixture to be lean under low load conditions and rich during high load conditions. A less-common version uses a linkage driven off the primary throttle shaft to mechanically move the power piston. "E" (Electronic Control Module controlled) series of Quadrajets use a computer controlled Mixture Control Solenoid that responds to electronic signals from the throttle position and oxygen sensors via the computer, ideal for precise fuel metering and allowing additional fuel under load. The solenoidcontrolled metering rods allow the fuel mixture to be very close to optimum, then the solenoid is pulse width modulated at about 6 Hz to fine-tune the air fuel ratio under closed loop conditions. The electronic versions have a throttle position sensor that is mounted inside the carburetor body, actuated by the accelerator pump lever. Quadrajet carburetors have mechanical secondary throttle plates operated by a progressive linkage (primaries open before secondaries) but use "on-demand" air valve plates above the secondary throttle plates. The air valves are connected by a cam and linkage to the secondary fuel metering rods. As the airflow increases through the secondary bores, the air valves are pushed down, rotating a cam that lifts the secondary metering rods. The secondary rods are tapered in a similar fashion to the primary metering rods, effectively increasing the size of the fuel metering holes as the rods are lifted and delivering more fuel. Therefore, the position of the air valve will control both fuel and air flow through the secondary venturis, even if the secondary throttle plates are fully opened. The end result is that the Quadrajet acts like a "vacuum secondary" carburetor and only delivers more fuel as it is needed. Advantages[edit] Significant positive features of the Quadrajet were: 1. Economy. Unlike most other four-barrel carburetors, the Quadrajet has a drastically different sized primary and secondary bores. The much smaller primaries act as a small two-barrel carburetor until you press the throttle enough to start to open the secondaries. The small primaries allow the primary throttle plates to be opened wider, and thus making the carburetor more efficient than a large two barrel, or square bore four-barrel. 2. Drivability. The small primaries also create better throttle response at part throttle application. The Quadrajet had a centrally located float that gave it excellent fuel control resulting in excellent street manners. 3. Off Road. The Quadrajet’s centrally located float is highly resistant to level changes caused by cornering or acceleration. The Quadrajet carburetor was actually a derivative of a variable venturi carburetor called the DOVE (diaphragm operated variable entrance) which was developed in the 1961-63 time frame at Rochester Products. Testing at the GM test facility in Arizona uncovered a hot OAT hot engine percolation problem which resulted in hot start difficulties because of flooded engines. Production of the DOVE, which was underway in 1963 when the hot start problem was identified, was suspended and a crash project was initiated to fix the problem. Simultaneously a second crash project was initiated to develop a modified DOVE which became the Quadrajet. Prototype Quadrajet carburetors were in test at Rochester Products by the Fall of 1963. The DOVE hotstart problem was corrected but not in a timely enough manner; the production DOVEs were destroyed and the Quadrajet took its place. Drawbacks[edit] This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (September 2007) A Quadrajet M4ME carburetor with electric choke. The Quadrajet went through several changes in its lifetime. Significant negative features of the Quadrajet were: 1. Its leaky fuel bowl. As in nearly all carburetors, the Quadrajet's bowl had pressed-in plugs used to seal holes left after drilling fuel passages during the manufacturing of the carburetor. These plugs in the Q-jet sometimes (especially when rough-handled during a rebuilding) leaked fuel causing; (a) a cold engine being hard to start, (b) erratic idling, (c) poor fuel mileage, and (d) excessive emissions. Many Quadrajets have their fuel bowl plugs sealed with epoxy when rebuilt to prevent leaks.[2] 2. The very small float bowl/fuel chamber can result in fuel starvation in extreme highperformance situations, but can always be traced to a fuel delivery problem to the carburetor, such as a weak fuel pump or a worn/rounded camshaft eccentric that drives the fuel pump lever. 3. The fuel inlet/fuel filter housing threads tend to be very fragile. [3] When care is not taken to align the insert, it is possible for the fuel inlet to cross-thread and to strip when tightened in the main housing. There are several "fixes" available in the aftermarket: New, oversized, self-tapping fuel filter inserts; new fuel filter inserts that seal with O-rings; and Heli-Coil re-threading kits. In nearly all cases, the carburetor will require disassembly and internal cleaning of the aluminum thread residue, especially up to and including the needle and seat, (needle valve), to prevent flooding. 4. Almost all Quadrajets today have some amount of warpage of the castings, [4] although less pronounced in the so-called "mod Quad" versions after 1974 which were a bit heavier and better designed to resist warping. The root cause of this warpage is overtightening the front two carburetor mounting bolts, often in combination with a base gasket that lacks hard nylon inserts for the bolt holes. 5. Over much use, the steel primary throttle shaft will tend to wear the aluminum casting material in the throttle body. This results in a minor air leak and in extreme cases, can cause the primary throttle blades to not close properly. This results in poor idle quality. The aftermarket has responded; several vendors are supplying repair kits for the carburetor body, generally in the form of teflon bushings. Variants[edit] A major change to the Quadrajet was implemented for the 1975 model year. These newer carburetors are considered "Modified Quadrajets" or "Mod Quads". In addition to the casting revisions that result in a physically larger carburetor, the primary metering rod length is different from '74 and older Q-Jets. They were also equipped with a self-contained choke mechanism that no longer relied on an intake manifold mounted choke, and a number "1" was added to the beginning of their identification numbers. Quadrajet carburetors were also built under contract by Carter. This seems to have happened at times when Rochester's facility could not keep up with demand. Carter-built Quadrajets will have the name "Carter" cast into them, but are functionally identical to the Rochester-built equivalent. The "newest" Q-Jets were built for, and sold by Edelbrock. There were several versions made, for both stock replacement and "performance" applications. One version was specifically intended as a replacement for Carter Thermoquad carburetors. The Edelbrock Q-Jets have been discontinued, although at this time Edelbrock still supplies some replacement parts. The twist-beam rear suspension (also torsion-beam axle or deformable torsion beam) is a type of automobile suspension based on a large H or C shaped member. The front of the H attaches to the body via rubber bushings, and the rear of the H carries each stub-axle assembly, on each side of the car. The cross beam of the H holds the two trailing arms together, and provides the roll stiffness of the suspension, by twisting as the two trailing arms move vertically, relative to each other. Contents [hide] 1 About 2 Advantages 3 Disadvantages 4 References 5 External links About[edit] The coil springs usually bear on a pad alongside the stub-axle. Often the shock is colinear with the spring, to form a coilover. This location gives them a very high motion ratio compared with most suspensions, which improves their performance, and reduces their weight. The longitudinal location of the cross beam controls important parameters of the suspension's behaviour, such as the roll steer curve andtoe and camber compliance. The closer the cross beam to the axle stubs the more the camber and toe changes under deflection. A key difference between the camber and toe changes of a twist beam vs independent suspension is the change in camber and toe is dependent on the position of the other wheel, not the car's chassis. In a traditional independent suspension the camber and toe are based on the position of the wheel relative to the body. If both wheels compress together their camber and toe will not change. Thus if both wheels started perpendicular to the road and car compressed together they will stay perpendicular to the road. The camber and toe changes are the result of one wheel being compressed relative to the other.[1] Conceptual model of a twist beam suspension. The green segments illustrate the axle stub centerlines. At rest the axles are in line and the wheels are vertical (Camber = 0 degrees) The twist beam suspension with the left axle deflected upwards. The deflected wheel now has negative camber. The left and right axles are no longer aligned. The right wheel's camber has changed to positive due to the deflection of the left wheel. Single wheel deflection (deflection due to roll) vs both wheels up (deflection in bump). Note that when both wheels are deflected the axles remain in line and the wheels have no camber change. Single wheel deflection shown vs both wheels at rest. Both wheels shown deflected up (bump) and at rest. Note that the axle halves remain in line and the wheel camber does not change. This suspension is commonly used on a wide variety of front wheel drive cars (mainly compacts and subcompacts), and was almost ubiquitous on European superminis. It dates at least to the Saab 95 and 96, which were produced from 1960 until 1978 and 1980, respectively. It was popularised by Volkswagen when they changed from rear engined RR layout cars in the 1970s, to front wheel drive FF layout cars. This suspension is usually described as semi-independent, meaning that the two wheels can move relative to each other, but their motion is still somewhat inter-linked, to a greater extent than in a true independent rear suspension (IRS). This can mildly compromise the handling and ride quality of the vehicle. For this reason, some manufacturers have changed to different linkage designs. As an example, Volkswagen dropped the twist-beam in favour of a true IRS for the Volkswagen Golf Mk5, possibly in response to the Ford Focus' Control Blade rear suspension as well as the Hyundai Elantra (HD) or newer and Hyundai i30. General Motors in Europe Vauxhall/Opel have continued to use twist- or torsion- beam suspension. This is at a cost saving of €100 per car compared to multi-link rear suspension. [2] Their latest version as used in the 2009-on Opel Astra uses a Watts linkage at a cost of €20 to address the drawbacks and provide a competitive and cost effective rear suspension.[3] The Renault Megane and Citroen C4 also have stayed with the twist beam.[4] Advantages[edit] Low cost Can be durable Fewer bushes than multi-link suspension that are less stressed and less prone to wear Simple Neat package, reduces clutter under floor Fairly light weight Springs and shocks can be light and cheap No need for a separate sway bar the axle itself performs that function Disadvantages[edit] Basic toe vs lateral force characteristic is oversteer Since toe characteristics may be unsuitable, adding toe-control bushings may be expensive. Camber characteristics are very limited. Not very easy to adjust roll stiffness Welds see a lot of fatigue, may need a lot of development Not much recession compliance - can be poor for impact harshness, and will cause unwelcome toe changes (steer effects) Wheel moves forward as it rises, can also be poor for impact harshness (this can be negated by designing the beam with the mounts higher than the stub axles, which impacts on the floorpan height, and causes more roll oversteer) Need to package room for exhaust and so on past the cross beam Camber compliance may be high Will cause tyre wear due to road camber[citation needed]