Sunday, October 27, 2013
NA Rotary Engine Factory Specs
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.
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