RX-7 Engine Information

About Rotary Engines

Rotary engines are internal combustion engines that use a design that is very different from the traditional cylinders of a piston engine. Instead of combustion occurring in a series of cylinders, a triangular rotor rotates within an ovular chamber, sealing off different compartments within the space for each stage of the four stroke process to occur. Each step in that process (intake, compression, ignition, and exhaust) happens in a different section of the chamber. The rotor remains in constant motion and engages the driveshaft to power the vehicle. Rotary engines may feature any number of combustion chambers, which are typically stacked in top of one another (just as a row of cylinders are lined up next to each other in a multi-cylinder piston engine). Beyond these fundamental differences in design, a rotary engine functions much like a piston engine, using a spark plug to ignite a mixture of air and fuel as the central element of a four-stroke process.

Rotary engines were among the first internal combustion engines built. They were first produced during the 1880s and became popular in the early 20th century as aircraft engines. German engineer Felix Wankel designed the Wankel rotary engine in the 1950s, bringing new interest to what was then considered a somewhat old-fashioned design.

In 1965 Mazda began using Wankel rotary engines in its passenger cars. The first such engine was designed "10A" and featured two rotors with a combined displacement of 982 cc. In 1970 Mazda engineers adapted the 10A by boring it out, increasing displacement to 1146 cc. The new version was dubbed "12A" and was the first engine offered in the RX-7 when it became available in 1978.

The 12A rotary engine was the original engine for the RX-7. It was rated at 100 horsepower. A 165-horsepower turbocharged version of the 12A was offered on some RX-7 models sold in Japan in the mid-1980s.

Since 1974 Mazda had produced a separate Wankel rotary engine known as the 13B. This engine first appeared in the RX-7 for the 1984 model year. In 1986 a new generation of the RX-7 was introduced, featuring a variant of the 13B rotary engine. This was known as the 13B-DEI. This engine added fuel injection and gave the new RX-7 146 horsepower. For the late-'80s and early-'90s, a turbocharged 13B engine was offered in RX-7 Turbo models. The turbo version produced up to 200 horsepower. The 13B-REW was a twin-turbocharged version of the same engine, making 280 horsepower and appearing in a select few of the final RX-7 models produced.

All RX-7 generations were designed with their Wankel rotary engine positioned at the front of the car bot behind the front axle. This placement is known as a front-midship configuration and helped the RX-7 achieve better weight distribution. Coupled with rear-wheel drive, the RX-7 offered competitive performance numbers and was praised for its power and handling.

In most model years, Mazda offered the RX-7 with either a 4-speed automatic or 5-speed manual transmission. Beginning in 1986 the RX-7 rotary engines were made with variable intake valves, which partially accounted for the rise in horsepower. Still, emissions remained low and fuel efficiency was generally good.

The Wankel rotary engines used in the RX-7 all featured distinct advantages over other types of engines, but there were also drawbacks typical of rotary engines in general. On the positive side, the RX-7 engines were extremely lightweight despite their power, which helped the RX-7 achieve impressive performance numbers. Their mechanical simplicity meant fewer repairs were needed over the lifetime of the engine. This durability also meant that the engines were seldom victims of complete mechanical failure.

The same unique design that made the RX-7 engines perform so well was also the result of some of their common problems. Over time the engine seals generally develop gaps, which can result in a loss of fuel efficiency and power output. The engines also tended to burn a small amount of oil, requiring frequent monitoring of the engine oil so that more could be added as necessary.