The best-selling cars of all time includes the Volkswagen Type 1 – the original Beetle. VW made this car with only minimal changes from 1945 through 2003. The total number of Beetles built was 21,529,464, but the same engine design also drove millions of VW Microbus vans, Karmann Ghia sports coupes, roundbacks, squarebacks, and Things. The VW air-cooled engine is one of the most popular powerplants ever made.

Volkswagen made versions of this engine for boats, airplanes, stationary power generators, pumps, and many more industrial applications. With a few key differences, the same engine design drove the legendary Porsche 356 and 550 Spyder, as well as the Porsche 912 through the mid-1970s.

The VW air-cooled engine is based on Depression-era needs. The engine is air-cooled so it can be made inexpensively. The engine uses a low-compression design so it can run on any fuel and be reliable. But the main feature that defines the Volkswagen engine is the flat-opposed four-cylinder design, which makes the engine compact. The Flat-4 design was invented by Karl Benz in 1897 and developed by Ferdinand Porsche. After VW, automakers including Tucker, Ferrari, Alfa-Romeo, Subaru, and many others have chosen flat-opposed designs to get the same benefits.

The basic VW air-cooled engine

In the VW design, the engine block is a two-piece crankcase made of pot metal aluminum alloy. The camshaft is captive in the crankcase, underneath the crankshaft. Miraculously, the crankcase seals well enough to keep the oil from leaking too much, although these engines all develop leaks over time.

Then the pistons ride in replaceable steel barrels with fins for heat radiation. You can shim or trim the barrels to change the compression ratio. The cylinder heads are made of aluminum. Large steel studs anchored in the crankcase hold the halves together and sandwich the cylinder barrels between the heads and the crankcase. Pushrods operate in flexible tubes beneath the cylinders. The pushrods are hollow to bring pressurized oil out to the valvetrain, and then back to the sump through the flex tubes.

The VW engine uses a single throat downdraft carburetor. A simple pipe manifold brings air-fuel mixture to the heads. The exhaust ports are on the front and rear sides of the heads. A simple exhaust system provides cabin heat and directs exhaust out to the rear of the car.

The VW air-cooled engine design uses a single fan belt driven by the crank pulley, and driving the generator and cooling fan. The engine has shaped sheet metal that directs the cooling air through the full-flow oil cooler and then down over the cylinder barrels and out of the car. The distributor and fuel pump are also crank-driven.

Growing displacement over time

The original postwar production VW air-cooled engine displaced 1,100cc and made 25 horsepower. VW soon enlarged the engine to 1,200cc and 36 horsepower. VW later boosted the 1,200cc engine to 40 horsepower.

In the 1960s, VW went through 1,300cc and 1,500cc transition models before coming to the 1,600cc single intake port design, and then the 1,600cc dual port design at 60 horsepower, that lasted through the end of production. Fuel injection came in late in the game, and had more to do with emissions requirements than performance.

Performance improvements

The basic VW air-cooled engine is a favorite for off-roaders and racers because the meager horsepower numbers from the factory are very easy to improve with just a few simple changes.

Because you will typically replace the pistons and cylinders at rebuild time, you can easily change displacement. If you choose the 1,600cc engine, you can upgrade as far as 1,776cc without making any changes to the crankcase or heads. Displacement upgrades past 1,776cc to the 2.0-liter range are available, but require upgrades to the crankcase as well.

VW heads respond well to porting work. If you combine that work with a twin-carburetor setup (as installed 0n the related Porsche 356/912 models) you can enjoy a nice power boost. Weber 40IDF and Solex/Kadron carburetors are popular induction upgrades.

Through 1965, VW products used 6-volt electrical systems. You can upgrade to a 12-volt system, but you must replace the generator, light bulbs, coil, and any gauges. You can continue to use the 6-volt starter, which will turn over rapidly, but also wear out sooner.

You can easily replace the stock distributor with a common aftermarket Bosch 009 unit for better spark advance. This yields another small performance boost.

Strong and weak points

The VW air-cooled engine design is inherently strong, even with only three real main bearings, because the crank is shorter than most four-cylinder designs. There’s an extra bearing for the crankshaft nose, just behind the pulley. It’s there to support the cam, fuel pump, and distributor drives.

You can align-bore the aluminum case during a rebuild. Bearings are available oversized on the outside diameter and undersized on the inside diameter to match the condition of both the case and the crank.

The oil cooler is mounted on the left side of the engine. Cooling air passes through the cooler before arriving at the left side (3-4) cylinders. There is no impediment to air flowing to the right side (1-2) cylinders. Failures like cracked valves and holed pistons tend to be concentrated on the left side. Specifically cylinder #3 is forward on the car and tends to be the hottest.

Motorsports use

The basic air-cooled VW engine has seen a lot of use in motorsports through the years. Many organizations including SCCA still support the “Formula Vee” open wheel class. This class uses the 40-horsepower 1,200cc engine in essentially stock form.

The VW engine is also popular in off-road racing. Virtually every sanctioning body has a class for Baja Bugs or buggies powered by VW air-cooled engines.

Beyond racing, the Volkswagen engine is a popular choice for sporting applications in dune buggies, sand rails, and other off-road vehicles.

The future for VW air-cooled engines

With tens of millions in the world, the VW air-cooled engine is a safe choice for any project. You’ll get an engine that delivers respectable torque for its displacement, longevity, simplicity, and even good fuel economy. The recent resurgence of interest in dune buggies and air-cooled VW applications makes a basic VW air-cooled engine a good investment.