GM Built An Ingenious Hybrid In The 1960s And Then Everyone Forgot About It

Roll call! What do you think was GM’s first hybrid? It’s not going to be the Chevy Volt, as that hit the market in 2010. Nor was it the Saturn Vue from 2007, as while the Vue was offered with a Green Line mild hybrid version, there were earlier hybrids from GM. In fact, GM’s first hybrid passenger vehicle sold to the buying public, outside fleet use or prototypes, was the Chevy Silverado/GMC Sierra Hybrid, which was launched in 2004 and sold to retail buyers between 2005 and 2007. It was a mild hybrid setup with an electric motor inside the transmission’s flywheel housing.

However, if we also take prototypes and studies into account, the first hybrid GM ever displayed was the Stir-Lec. The vehicle bearing that futuristic and mysterious name was an Opel Kadett coupe with a very weird experimental hybrid set-up, in 1968. In the mid-1960s, severe smog became a public health crisis, and since General Motors had put many polluting cars on the roads, it directed funds into researching alternative means of propulsion other than regular gas or diesel.

The Basic Car Was Good Looking

The Opel Kadett was one of those perfectly ordinary European family cars. The Kadett name was already used in the 1930s on a small and basic car that later spawned a Soviet copy, the Moskvich 400, that was produced until the mid-1950s. In the early 1960s, the Kadett was reborn. You might recognize the Kadett A as the “Oliver” car from Top Gear’s Botswana Special. These are small and friendly-looking cars, and while the Kadett B introduced just a couple of years later was somewhat larger, it was still compact enough to be sold as a small car at Buick dealers in the United States. That was also the Kadett, which Bob Lutz famously put on its roof.

The following generation, the Kadett C, was largely the same car as the Chevrolet Chevette, the Vauxhall Chevette and the Isuzu Gemini/I-Mark, as it was built on GM’s T-Body platform.

Stir-Lec For Stirling-Electric

In the late 1960s, General Motors let journalists behind the wheel of its experimental vehicle, built by GM’s Research Laboratories. Clothed in a production car body, the Stir-Lec was an early EREV prototype designed in the face of the growing smog situation in the United States. How about a commuter car that didn’t emit any meaningful exhaust gases?

A bunch of small European cars of the time had the engine in the back, while the Kadetts were front-engined. The Stir-Lec changed that, as the car’s engine was located in the trunk, and attached to the differential was a three-phase, 20-horsepower electric induction motor, small and compact, powering the rear wheels via batteries mounted in the front.

The rear-mounted engine, running at a constant 2,800 rpm, had the sole job of keeping the car’s batteries charged, and had no connection to the driven wheels. And it didn’t run on gasoline, as it was a Stirling engine that could even run on helium. Mind-boggling stuff, especially for the late ’60s.

What’s a Stirling engine, you may ask? It mustn’t be confused with a Sterling engine, which is a 2.7-liter Honda V6 fitted in a Rover 800-series exported to the US.

The Stirling engine was invented by its namesake, the Scotsman Robert Stirling, and it’s a closed-cycle regenerative heat engine, also called a hot air engine, patented by Stirling already in 1816. As The College of Science and Mathematics at Fresno State explains the basic premise:

Stirling engines are more efficient forms of generating power from heat energy than standard combustion engines. The greater the temperature difference between the interior and exterior, the more efficient the generation. The two pistons of the engine are connected via a pressure chamber that allows air to flow between them. The ‘hot-side’ of the piston is exposed to the flame and heats up while the ‘cold-side’ is cooled by the ambient air temperature. Thermal expansion causes the heated air to push the hot-side inward, forcing the cool-side up. The air moves into the cool-sides chamber, where it cools and condenses. This condensation causes the cool-side’s piston to contract, the momentum of which draws the cooled air into the hot-side and forcibly compresses it further. The flame then again heats and expands the air, forcing the piston back inward, repeating the cycle.

The “cool side” in the Stir-Lec was water-cooled with a rear-mounted radiator and fan setup, with a separate blower for the combustion air. The working gas, hydrogen in this specific case, is permanently retained in the engine.

The downside is a low power-to-weight ratio. However, for keeping 6 kWh worth of batteries charged, it’s fine, and the Stir-Lec’s engine produced just eight horsepower. The engine was produced by the Dutch company Philips, which had been producing Stirling engines to be used as power generators, like the one in the above video. While that generator doesn’t run silently, I guess it would make a lot less noise clothed in a car body, even inside a 1968 Opel Kadett.

It Wasn’t Fast

Under the hood, the radiator’s place was taken up by the modulating inverter and 14 completely conventional, commercially available lead-acid batteries. Running on battery power only, the car would have a range of just 15 to 30 miles depending on how much the throttle pedal was pressed, but the Stirling engine setup (which did its own mashing of the gas) worked as a range extender, giving it a usable range of 150-200 miles out of 4.75 gallons of kerosene. As much as 42 mpg with barely any exhaust pollution isn’t bad at all, but it’s not like you would cover ground very fast.

The entire experimental vehicle weighed some 3,100 lbs with the front seats occupied, which is heavy for a Kadett.

Since the Stir-Lec was widely shown in 1969 magazine ads, it’s often noted to have been unveiled that year, but Popular Science test-drove the first version, the Stir-Lec I, already in 1968. The magazine said it wasn’t fast, as acceleration to 30 mph took “10 to 20 seconds”, which is an interestingly wide span, but the take-off was said to be very smooth.

During the test, the Stirling engine was fueled using kerosene. The article also says that 30mph is the “break-even” speed, where the car can travel without draining the batteries faster than it can recharge them. A second version, the Stir-Lec II, followed in 1969, which swapped the AC motor for a DC one, and the electronics were simplified further. Range wasn’t improved, but the car was slightly faster. The prototypes had both the trunk and the frunk full of stuff, and GM never developed the Stir-Lec cars to the production phase.

In 1973, Ford was developing a 170-hp Stirling engine together with Philips, reportedly to replace the 351 Cleveland in the Ford Torino, but it doesn’t seem to have been significantly more economical.

In 1971, GM also showed the XEP-1a experimental vehicle, which was based on a similar Opel Kadett as the Stir-Lec cars. It was a more conventional electric car prototype, just full of batteries without a range extender, and it worked as a test mule for Opel’s record-breaking Elektro GT.

The Opel GT-based prototype reached a top speed of 188 km/h (116.8 mph), with 1630 lbs of Varta nickel-cadmium batteries providing power. The entire car weighed as much as an Opel Blitz truck, or over 3700 lbs. When you know how small an Opel GT is, it puts that into proper context.

While the 1968 Stir-Lec was GM’s first hybrid prototype, GM also showed another hybrid prototype the next year. That was the XP-883, a tiny fiberglass nugget with a plug-in hybrid system. The engine was a 35-cubic-inch two-cylinder, coupled to a DC motor and six 12-volt batteries in the rear. Setting off, the car would run on electric power until it reached 10 mph, after which the engine turned on. The XP-883 would accelerate all the way to 60 mph, taking a whole 28 seconds to do that; 40mph was attainable in a more palatable 12 seconds.

Like the Stir-Lecs, the XP-883 remained an experimental prototype, and it took until the 1990s for GM to actually provide an electrified car for regular customers, with the EV-1 – which was strictly limited in the way it was distributed, too, as you could only lease them. The 2010 Chevrolet Volt, again championed by Bob Lutz, was a moonshot when you consider how long it took for GM to sell hybrids to people who wanted to save a bit of fuel and run on electricity when it suited them.

Top graphic images: Opel; Popular Science