Chevy Experimented With A 2-Rotor Corvette In '73

What's the first thought that comes to your mind when someone says Corvette? For some, it's a white Corvette C4 driven by Burt Reynolds as he drives off into the sunset in a glorious V8 symphony. We're not sure if you have the same vision, but it's hard to imagine the Corvette without a big V8 engine under the hood. And you'd probably never imagine one with a rotary engine. But Chevrolet came pretty close to making a two-rotor Wankel Corvette in '73.

It was called the XP-897 GT, a gorgeous mid-engine two-seat concept sports car with a two-rotor Wankel engine meant as General Motors' opening rotary act. Most of the credit for the rotary Corvette goes to Ed Cole, GM's legendary president and one of the visionaries behind the original small-block V8. Ed saw the rotary engine as a major part of the technological future and became one of its biggest evangelists in America. He envisioned a compact, lighter, and more powerful engine that would be a better fit for the other mid-engine concepts (the XP-882 and 895) that were already in the works. Spoiler alert: a mid-engine Corvette did not go into production until 2020. But it almost became a reality in the early seventies thanks to the rotary XP-897 GT.

But why move from a proven V8 power train? What made the Wankel more appetizing than the V8? Why didn't it take off? And what even is a Wankel engine?

It wasn't just Chevrolet looking to get into Wankel engines. AMC, Chrysler, Ford, and Mercedes-Benz were looking at the Wankel rotary engine as if it were the promised messiah. Even the Soviets made rotary-powered Ladas for the KGB. There were many reasons for this interest in the rotary engine. One was the motor's inherent simplicity. Unlike traditional engines that have to convert reciprocating motion of the piston into power, the Wankel engine made its power in a rotary motion. This meant that the motor needed far fewer moving parts. As a result, it was lighter, smaller, simpler, and more refined than your traditional engine. It also offered a superior power-to-weight ratio compared to the engines of that time.

The seventies also marked the arrival of Mazda, a brand that proved the Wankel engine could work. The Japanese carmaker entered North America with its rotary Cosmo sports coupe, and continued the tradition with its RX series of sports cars. Not wanting to be left behind, General Motors spent millions to make plenty of rotary-focused moves, from creating its own engine designs to building prototypes for AMC. But, of course, the crowning glory of these efforts was the rotary Corvette.

Despite its pros and cons, many liked the idea of a Wankel rotary engine. It's a completely unique concept that turns what we know about the conventional four-stroke engine on its head. At its core, the fundamental difference between traditional and Wankel engines is reciprocating motion versus rotary motion.

A rotary engine has an oval-shaped housing with a triangular rotor rotating inside it, unlike a conventional four-stroke engine, which has a tube-shaped combustion chamber with a piston moving up and down. This rotor moves inside the oval chamber in a funky orbital pattern, which leaves three distinct gaps between the side faces of the triangular rotor and the housing. Instead of intake and exhaust valves, the housing has ports. The Wankel engine uses the same four-stroke cycle – i.e., intake, compression, combustion, and exhaust. The difference, though, is that all three sides of the rotor simultaneously deliver their version of the combustion cycle. When one face is in the intake cycle, the other is in the combustion cycle.

This unique way of working has the Wankel motor complete three combustion events within one full rotation of the rotor. The Wankel engine is also compact as there are fewer moving parts compared to a traditional engine (no pistons, connecting rods, valves, or camshafts). With fewer parts and a pure rotatory motion, you have a vibration-free, smooth, high-revving engine that feels way more advanced than the rumbling V8s of the seventies.

Yes, the XP-897 GT sat on a modified Porsche 914/6 platform, which was specifically designed to house the new General Motors' two-rotor Wankel engine. Why? Because Ed Cole wanted a compact mid-engine chassis for his compact rotary engine. The Porsche platform's wheelbase was reduced by 6.5 inches while the front and rear tracks were widened. The concept car even featured Porsche suspension and brakes.

The engine was not a rebadged Mazda power train. It was built in-house by GM, and it cost the company an obscene amount ($50 million back then) to license from Wankel and NSU. And it wasn't made specifically for the Corvette, but was initially meant to debut in the Chevrolet Vega. The water-cooled twin-rotor engine displaced 266 cubic inches (or 4.4 liters) and delivered 180 horsepower.

The 914/6 was sent to famed Italian coach builder Pininfarina. That company worked its magic and created a sleek, low-slung sports car painted in silver, which featured silver leather seats. It was the best-looking Corvette of all time. Before showcasing it at the 1973 Frankfurt motor show, GM changed the XP-897 GT's color to a bright red and the interiors went from silver to fawn leather. The concept car now sported gold-painted machined alloy wheels (which later came to be known as "Vector" wheels). After all these changes, Corvette gave this concept the name of "Corvette Two-Rotor".

In theory, the rotary engine was a masterpiece in automotive technology. In practice, though, it was flawed. For starters, the combustion chamber design did not allow fuel to cleanly burn, which resulted in poor fuel economy. Other challenges included the motor's voracious appetite for engine oil as well as poor rotor seals, which often failed with disastrous consequences. Mazda soldiered on with rotary engine technology, perfecting it as much as possible. Eventually, they gave up and dropped the rotary engine in 2012 after the RX-8. Mazda's rotary engine is making a comeback, though, in a new, greener concept avatar.

There were other factors as to why the Corvette Two-Rotor didn't make it to production. GM realized that the deeper they went in, the more the once-pioneering rotary technology felt like snake oil. The 1973 fuel crisis and tightening emissions norms posed major hurdles. And the mid-engine layout, though revolutionary, was a complex and costly exercise at that time. By 1974, GM finally shut down its Wankel engine development department.

So what happened to the Corvette Two-Rotor Concept? GM stored it at Vauxhall's Design Center in England for over a decade before finally deciding to scrap the car instead of paying taxes to bring it back to the States. Thankfully, UK-based Corvette collector Tom Falconer convinced GM to sell the concept car to him. Although he got his hands on the car, it ended up going without the power train. The enterprising Tom filled the engine gap with a Mazda 13B rotary and turned the concept into a show car, allowing it to continue surviving today.