Rotary engines are used in aircraft, snowmobiles, jet skis, chainsaws and other applications where a small, simple, lightweight engine needs to produce a lot of power.
That was Mazda’s thinking when it introduced the RX-7 in 1978. With a cubic capacity of just 1,146cc, its engine was small enough to get a big road tax break in the domestic market and yet it belted out 100hp, enough to give the RX-7 a top speed of 120mph.
Three generations later, the RX-7 was finally phased out in 2002, after evolving into a larger, more sophisticated – and ever faster – sports tourer.
The first-generation model shown here ran from 1978 to 1983. The small size of the rotary engine (about a third of the size of a regular engine delivering the same power) allowed Mazda to mount it behind the front axle and achieve a near 50-50 front/rear weight distribution. It was so smooth that the rev counter had a buzzer to let you know it was approaching the 7000rpm redline.
So if rotary engines are so good, why haven’t they caught on? The design is simpler than a regular ‘reciprocating’ engine, using a triangular rotor within a specially-shaped chamber which also incorporates inlet and exhaust ports and spark plugs. The combustion process drives the circular movement of the rotor at one point in the rotation and exhaust gases are vented at another.
But while rotary engines are very efficient in terms of size, weight and power output, they are not particularly fuel-efficient. What’s more, an early reputation for unreliability, notably with the rotor apex seals in the NSU Ro80, hasn’t helped. Almost all of the technical issues around rotary engines have been resolved in the latest designs, but mud sticks.
Incidentally, it’s not ‘wankle’ but ‘van-kel’. It’s the name of German designer Felix Wankel, who first conceived the design in 1929. Many use the name ‘Wankel’ to describe rotary engines in general
