Separating fact from fiction when it comes to Mazda’s giant-killing rotary engine.
Mazda‘s rotary engine is one of the most unique — and often misunderstood — engines of all time. Mazda wasn’t the first company to build German engineer Felix Wankel‘s groundbreaking design – that honor goes to NSU. However, they were the only company to make it work well enough to put it into serious mass production and keep the rotary dream alive for decades.
Rotary engines are known for their simplicity and their tremendous power output relative to their size. A typical two-rotor Mazda rotary engine comprises just three moving parts. By contrast, a typical overhead cam four-cylinder is made up of dozens of moving parts. They’re also incredibly smooth, producing almost none of the engine vibrations we’ve become accustomed to.
Mazda rotary engines are also powerful relative to their small size, often being compared favorably to four- and six-cylinder engines with two or three times the displacement. Of course, there are some downsides to the design as well – otherwise, we’d all probably be driving cars with rotary engines right now.
Rotary engines are notorious for their poor fuel economy and short service intervals, and they consume a bit of oil by design. They require special care and attention during use as well, and even so, they often don’t last as long as their traditional piston-powered counterparts. With that said, if you’re prepared to deal with the care and feeding of a rotary engine, you’ll find that it provides a very unique – and rewarding – driving experience.
Mazda Rotary Engines: A Brief History
The German company NSU worked hard to develop the rotary engine, releasing a few groundbreaking, award-winning cars (like the Ro80) that eventually bankrupted the company due to persistent reliability issues. Mazda took the ball and ran with it, further developing the rotary engine into a reasonably reliable powerplant that powered all manner of Mazda vehicles, beginning with the Cosmo in 1967.
In the 1970s, Mazda truly bet nearly everything on the rotary engine. You could find the rotary engine in everything from family sedans to pickup trucks and even buses. Unfortunately, the fuel crisis – and heightened concerns about pollution – threatened to kill the rotary once and for all. Mazda, the small, scrappy company from Hiroshima, wasn’t going to let the rotary die without a fight.
Instead, Mazda decided to play to the strengths of the rotary engine, installing it in their new sports car, the RX-7, in 1978 (1979 in the U.S.). The result was a resounding success that, to this day, still maintains a loyal following of owners and enthusiasts. In 1991, Mazda entered the four-rotor 787b race car in the legendary 24 Hours of Le Mans endurance race and won, thanks to, of all things, its reliability and efficiency.
Since its introduction in 1978, over one million Mazda RX-7s and RX-8s have been produced in total. Does one deserve a space in your garage? We think so – assuming you’re willing to tolerate the engine’s unique idiosyncrasies.
Rotary Engine: How it Works
In a traditional piston engine, the rotating assembly moves, but the combustion chamber – the area inside the engine where the action happens – remains stationary. Air and fuel are combined, compacted, combusted, and finally expelled from the same area in each cylinder bore. A rotary engine utilizes the same four cycles, but the combustion chamber changes size and location as the rotor spins through its cycle.
Each rotor is shaped like a rounded triangle and spins inside of a rotor housing, which is shaped like an oval with its middle squeezed slightly. The air and fuel mixture enters the rotor housing, and the spinning motion of the rotor compresses it and “pushes” it toward the part of the rotor housing where the spark plugs are located. Each rotor uses two spark plugs, so while there are only two rotors, there are four spark plugs.
The spark plugs ignite the compressed air/fuel mix, and the rotor pushes it towards the exhaust ports as the combustion chamber expands again. This happens thousands of times per minute, and the rotary engine can operate at very high RPMs.
Rotary engines tend to make more power at higher RPMs, at the expense of low-RPM torque. Many drivers find great pleasure in operating a rotary engine at its limits, due to its smooth, turbine-like power delivery. Regularly running your rotary engine at higher RPMs is also said to prevent carbon buildup, which can be fatal to these engines. Like all engines, though, the Mazda rotary still has a redline, and some models actually have a buzzer installed to warn the driver if they are taking things a little too far.
One interesting characteristic of these engines is that they tend to deliver more or less the same fuel economy regardless of how spirited or conservative your driving style is. There is no “hypermiling” a rotary engine. This characteristic actually helped the Mazda 787b win Le Mans in 1991. It’s been said that the Mazda rotary engine is an ideal racing engine that’s less well-suited for street use. That’s an attractive feature to some enthusiasts, while others may look for a sports car with a more conventional powerplant.
That’s not to say that the Mazda rotary engine is high strung – not by a long shot. That said, if you’re just using your RX-7 or RX-8 for stop-and-go commuting in the city, you aren’t realizing the full potential of what this engine is capable of.
Rotary Maintenance
To complete its task effectively, the tips of the rotor must seal against the walls of the rotor housing in the same way piston rings do. This is accomplished with apex seals. The apex seals are lubricated with oil, and during high-RPM operation, a separate oil pump provides additional lubrication. This is why rotary engines consume a bit of oil, and why it’s important to check the oil often.
Many owners suggest an oil change interval of just 2,000 miles. Thankfully, there’s a way to keep costs down. Rotary engines seem to dislike synthetic oil as it tends to leave behind harmful deposits that actually increase wear. Most enthusiasts suggest using traditional oil in the engine to keep it alive for as long as possible. Since it’s cheaper than traditional oil, it’s a little bit cheaper to change.
Besides oil and spark plugs, there really isn’t much in the way of necessary routine maintenance. Rotary engines run hot – very hot – so it’s important to make sure that your cooling system is operating at its best at all times, especially if you live in a warm climate.
The newest version of the rotary engine, the 13B Renesis used in the RX-8, is more efficient than the previous versions it replaces. However, many owners – especially those with automatic transmissions – find that these engines can wear out after just 70,000 miles or less. It’s a theory in the enthusiast community that the extra strain placed by emissions equipment puts the engine under additional stress. Older rotary engines in RX-7s – especially the non-turbocharged models – seem to last quite a bit longer.
When the engine is worn out, it must be rebuilt or replaced. This can cost several thousand dollars and result in a lot of downtime, so it’s worth taking into account if you plan on keeping a rotary engine sports car around as your only mode of transportation. On the other hand, there really aren’t a lot of other things to go wrong with this engine. While other sports cars may nickel-and-dime you to death, the rotary engine takes an “all-or-nothing” approach. If you choose to buy one, prepare accordingly.
Respecting Tradition
Thankfully, there are things you can do to keep your rotary engine alive for as long as possible. Besides keeping an eye on your oil and coolant, it’s a good idea to let the car warm up to operating temperature before driving it. We suggest setting your alarm a few minutes earlier.
Even though Mazda doesn’t sell new cars with rotary engines anymore, they still support the powerplant with an engine rebuild program and a full line of replacement parts. There’s a healthy enthusiast community that works hard to support the rotary engine with parts, service, and advice. If you own a car with a Mazda rotary engine, it’s important to find a mechanic who specializes in them, but rest assured, they’re out there. The Mazda rotary community is a tight-knit group, and they’ll be happy to point you in the right direction.
Japanese sports cars, by and large, have a well-deserved reputation for being inexpensive to buy and own, with an easygoing maintenance schedule that’s very forgiving. The Mazda RX-7 and RX-8 are notable exceptions to this general rule. If you treat a Mazda rotary the same way you’d treat, say, a Nissan Z-car or a Toyota Supra, you’re likely in for a world of heartaches and headaches.
If, instead, you treat your RX-7 or RX-8 as the unique, exotic machine that it is, it can and will provide you with years of faithful, enjoyable service — and an experience that simply can’t be replicated in any other car, at any price.
Photos: DepositPhotos: Swatchandsoda; Artzzz; Hurricanehank
