Sometimes two engines are better than one.
Twin combustion engined cars are one of the real oddballs of the motoring world. It makes no sense as a drivetrain for a production car just on the basis of mechanical complexity alone, but there have been specific applications suited to the twin-engine approach. In race cars, it's cheaper than developing a bigger engine from scratch or a shortcut to all-wheel-drive if the details can be mastered. For vehicles designed to go off-road, the weight can be balanced and torque doubled by adding an extra engine. There has also been the crazy one-off home- or shop-built projects, but that's a whole other subject for another day.
The 2CV has always been an oddball car that could do way more than, at least on paper, it should. In the late 50s and 60s, the French were exploring for oil in North Africa, home of the Sahara desert and opted to use 2CVs. The twin-engine design of the 2CV Sahara makes a lot of sense when you start to think it through. The 2CV is light, surprisingly rugged, has flexible suspension with long travel, and has good ground clearance. All-wheel-drive via an engine in the front and rear keeps weight distribution even in the sand, the development time and cost is minimal, and, most importantly, the design builds in redundancy. Having your only engine fail catastrophically in the middle of the desert is deadly, but having one of two engines fail gives a fighting chance to get out again.
Mercedes first generation of the A-Class had rough entry into the world. When a magazine put the A-Class through the Moose Test (an avoidance maneuver performed at speed), a Swedish journalist rolled it over. It was a PR disaster that swept through the world's media, but AMG stepped up to the plate and had a crack at fixing the issue. Unfortunately, AMG's only tool was a hammer, and the solution the engineers came up with was to lower the A38 and put a second engine low down at the back. Double the engine didn't quite add up to double the power, but it still managed a 0-60 mph time of 5.7 seconds with a top speed of 143 mph. AMG made 4 or 5 prototypes but it never made it to market.
The legend that is John Cooper didn't come up with the idea for a twin-engined version of the original Mini, but when he drove a twin-engined Mini Moke put together by the BMC design team, Cooper was impressed by the increase in power and traction. He became obsessed with the idea and built a prototype twin-engined mini in just six weeks. He put a 1088-cc racing engine making 82 horsepower in the front and a tuned 1212-cc engine making 96 hp in the back. He then matched the ratios and strengthened the frame before terrorizing people on the public roads in it.
The mini Twini never raced, but extensive testing put down solid lap times at Brands Hatch. The original car, unfortunately, didn't survive for a museum. Cooper nearly died in an accident when something failed while he was driving it to a dinner party in 1965. The car rolled several times and left him with a severe concussion, amnesia, and cracked ribs. People haven't stopped recreating them though.
In 2007, everyone's favorite hairdresser car, the Audi TT, defied the silly stereotype at the hands of the Audi tuners MTM. A second tuned 1.8-liter turbo engine sat where the rear seats used to be, and both engines made 370 horsepower with an upgrade path to 501 horsepower each. It tested at 244 mph in Papenburg, Germany - a speed you still can't do in a stock Audi R8.
When it comes to lists of fun and thrilling cars to drive, the tenth generation Cadillac Eldorado is not a natural candidate. Warren Mosler has a lot of arrows in his quiver though. He's an economist, hedge fund manager, economic theorist, politician, as well as an engineer and the founder of Mosler Automotive. According to Mosler, the TwinStar was originally a project to make the Eldorado into a mid-engine car, but they realized it worked really well as a twin-engined car. That also had the benefit of being able to keep the rear seat. The conversion cost around $30,000 at the time and, after driving one, a race car driver employed by Road and Track claimed: "This thing's amazingly well-balanced."
The Hurricane concept was unveiled at the 2005 Detroit Auto Show. It used two 5.7-liter Hemi V8s developing 330 horsepower each. One of the features was cylinder deactivation that allowed the engines to run on 4, 8, or 12 cylinders instead of the full 16 and save fuel on the road. Another excellent feature was the steering and suspension system that allowed the Hurricane to spin 360 degrees on the spot like a crab turning. While it would never make it into production based on its complexity and cost, the concept did work.
In the early 1930s, Alfa Romeo was losing ground to its Grand Prix competitors. So, in 1935 someone came up with the bright idea of a twin-engined race car and got to work. Two cars were built and both were staggeringly fast in a straight line. One was built using 2.9-liter engines, but it was the one built with 3.2-liter engines that topped out at a recorded 208 mph. The strange thing about the Bimotor, and its singular because only one still exists, is that all that power is sent only to the rear wheels.
Saab was a brand that liked to play with unusual drivetrains and layouts, and the 93 Monstret is one of those. Saab jammed two 3-cylinder 2-stroke engines under the hood making 138 horsepower between them. The problem Saab found is that the aerodynamics of the bodywork caused the rear end to go light at high speeds and cause its handling to be a handful for the driver. Monstret translates into monster in English, and that's why the only one built earned the name.
Before Volkswagen owned Audi, it had a crack at competing against the Quattro in rallying. Volkswagen Motorsport came up with the idea of putting two 1.6-liter engines from the Golf GTI inside a Jetta along with a close-ratio gearbox and limited-slip differentials. It didn't do well in competition due to the low power-to-weight ratio, but it did lead to VW experimenting more with twin-engined cars. In particular, a Golf that nearly captured glory at Pikes Peak and was recently restored by VW.
If there's something familiar about the Tiger Racing Z100, that's because they are a kit car manufacturer in the same vein as Caterham in the UK that make stripped down sports cars. Owner Jim Dudley wanted to claim the 0-60 mph record in 2001, and to do that he fitted two Kawasaki ZX9R engines under the hood with separate sequential transmissions. It claimed the 0-60 mph record at 2.9 seconds, although an unofficial test clocked the Z100 at 2.8 seconds.
Seat had left ownership from the Fiat Group in the 1980s and wanted to take a swing at Group B rally racing with the Ibiza model. Unfortunately, economic and political unrest in Spain meant there wasn't a lot of money to play with and the brand would have to do it on a budget. All-wheel drive was still relatively new at the time and very expensive to develop. So two privateers, the Servià brothers, used the cheaper approach of using two engines to power two wheels each. They used a pair of tuned 1.5-liter engines mated together using two front floor pans welded together and the roll cage to provide the necessary rigidity. The brothers went on to take podiums and class wins in the Spanish rallying championships.