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Carburetors deliver a combination of air and fuel to internal combustion engines. These components use intake and exhaust valves to divide and transport the air-fuel mixture into the engine. The Rochester carburetor came about in 1965, when General Motors (GM) began using them in its vehicles with eight-cylinder engines; GM continued to install the carburetors in its vehicles for nearly 20 years. As of 2011, you can purchase an aftermarket Rochester carburetor, also called a Quadrajet.

Rochester B

The Rochester B carburetor had a float level of 1.28 inches and a float drop of 1.75 inches. The idle vented at 0.05 inches with the engine stopped in an idle position and the choke open. The Rochester B had a bowl vent of 3 internal and 1 external idle, while the 292 version had a bowl vent of 2 internal and 1 external idle. The throttle bore measured 1.563 inches for the Rochester B, but 1.75 inches for the 292 version. The main venturi for the 230 Economy version measured 1.063 inches, the main venturi for the 230 P and 230 version measured 1.594 inches and the main venturi for the 292 version measured 1.625 inches. The small venturi for all Rochester B versions measured 0.594 inches. The Rochester B pump discharge jet measured 0.031 inches, while the 292 versions measured 0.035 inches. The idle speed jet measured 0.067 inches, while the 230 Economy versions measured 0.057 inches.

Rochester 2G

The Rochester 2G had a float level of 1.359 inches and a float drop of 1.906 inches. It had a bowl vent of 1 inside. The throttle bore measured 1.438 inches, while the pump discharge measured 0.026 inches. It had main venturi of 1.094 inches and a small venturi of 0.125 inches. The main metering jet measured 0.053 to 0.054 inches.

Rochester 4G 348 and Rochester 4G 409

The Rochester 4G 348 had a primary float level of 1.625 inches and a secondary float level of 1.688 inches. It had a float drop of 2.25 inches and a bowl vent of 2 inside. The throttle bore measured 0.438 inches, and the primary discharge jet measured 0.026 inches. It had a primary main venturi of 1.125 inches and a secondary main venturi of 1.25 inches. The small venturi measured 0.25 inches. The 348 versions primary main metering jet measured 0/055 inches, while the secondary main metering jet measured 0.069 inches. The 409 versions main metering jet measured 0.054 inches, and the secondary main metering jet measured 0.067 inches.

Idle Specifications

The idle speed jet for the Rochester B measured 0.067 inches, while the 230 economy version measured 0.057 inches. The Rochester 2G 283 versions idle tube measured 0.028 inches, the 327 versions measured 0.031 inches and the 348 versions measured 0.037 inches. The Rochester 4G carburetors primary idle tube measured 0.027 to 0.028 inches, and the secondary idle tube measured 0.040 inches.

The rotary engine is a highly unusual and very rare power plant. Its sole application in road legal passenger vehicles is found in Mazdas RX-8 sports car. The compact dimensions and low weight of the engine allow Mazda to keep the RX-8s center of gravity near the ground and weight quite low, making it one of the best handling cars on the road today.

Basic Specs

Rotary engines have radically different designs than conventional motors and use a "rotor" (hence the name) instead of cylinders. The rotor is a triangular, lightweight piece mounted on a circular lobe. The rotor compresses the gas/air mixture simply by rotating on the lobe and therefore does not need pistons, camshafts or rods. Concepts such as bore and stroke do not apply to rotary engines. The capacity of a rotary is defined by the maximum volume it can compress and ignite per cycle, which for Maxdas rotary is 1.3 liters.

The compression ratio is 10:1, with multi-port electronic fuel injection igniting the mixture during the compression stroke. The rotor is housed in an aluminum chamber with chrome-steel liners. Exhaust gasses flow into stainless steel headers, which then connect to a low back pressure main muffler. Transmission options for the engine are a six speed manual or six speed automatic

Power and Torque

In addition to its light weight and compact dimensions, a chief advantage of the rotary engine is its ability to reach very high engine speeds. The Mazda rotarys redline is a stratospheric 9,000 rpm when mated to a manual transmission, and 7,500 rpm when combined with the automatic, as the later transmission is unable to cope with higher speed and torque. Due to the restriction in engine speeds, the maximum power also varies based on the choice of transmission. While the engine makes 232 horsepower at 8,500 rpm with a manual transmission, with the automatic it produces 212 horsepower at 7,500. This difference is solely the result of engine speed restrictions, as evidenced by the fact the the motor produces an identical peak torque of 159 pound-feet at 5,500 rpm regardless of transmission type.

Performance

This fast-spinning engine propels the RX-8 from zero to 60 miles per hour in six seconds flat when paired with the manual and six and a half seconds with the automatic transmission. Fuel economy is relatively poor in either case however, especially considering the 3,000-pound weight of the whole car, which is very light for a four-seater. Both the manual and automatic vehicles achieve 16 miles per gallon in the city. While the manual version gets 22 mpg on the highway; the automatic can squeeze one more mile from each gallon, due to its longer final gear ratio. Although both transmissions feature six forward speeds, the manuals final ratio is 0.79 while the automatics tops at 0.58.

Excess fuel consumption is practically unavoidable with rotarys and is the main reason these engines are not more commonly used in modern automobiles. The unique design not only allows a significant amount of unburnt fuel to escape the combustion process, but also results in a good deal of energy being wasted as heat.