Cars with radial engines

Gallery opened 18 Dec 2019

Updated: 18 Jan 2020

Rohrbach Concept added

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Car engines have been made in many formats; in-line. horizontally-opposed, V-block and so on. However so far as cars are concerned, probably the rarest type is the radial engine, in which the cylinders are arranged in a circle. In a four-stroke radial engine there has to be an odd number of cylinders to obtain a sensible firing order.


Colin Lucas was a well known English architect in the nineteen-twenties and thirties. He collaborated with Oliver North to build this aerodynamic car. It had a single headlight, and a boat-shaped body with a roof of translucent canvas.

There are some biographical details on what I think is the right Colin Lucas here but there is absolutely no mention of a car.

Left: The North-Lucas car: 1922

This looks a bit like streamlining but it probably isn't very aerodynamic. The vertical sides and near-vertical windscreen suggest that the drag coefficient would not have been impressive. The rear-engined prototype had a top speed of 55 mph, which doesn't seem very quick from a 1.5-litre engine.

For those (excusably) in doubt, the front of the car is at the left. There is a large intake for the air-cooled engine just behind the spare wheel.

Left: The 5-cyinder engine of the North-Lucas car: 1922

The engine sat on top of the transmission; there were finned inboard brakes and the suspension was by swing-axles.

The induction manifolds vanish under the flywheel; was the carburettor there? Note that the exhaust manifold is not shown. An aeroplane radial engine could use stub exhausts, but a road car would have to have the exhaust from the five cylinders collected into a silencer, and this must have been a serpentine piece of plumbing.

It has been remarked that the fan-blades on the flywheel are well-situated for slicing off the fingers of anyone examining the engine when it was running.


Julian Brown inherited a $2.5 million fortune from his industrialist father, and spent much of it on developing engines and cars that never reached production.

Left: The Julian sport coupe: 1927

Julian Brown designed the aluminum body, which was then constructed by the
Fleetwood Metal Body Co. It was finished and mounted on the backbone chassis in 1925.

Left: The Julian sport coupe: 1927

The steel backbone frame consisted of a 4.5-inch central tube, with two 2.0-inch crossmembers fixed to it at front and back. The cross-members supported the aluminum five-passenger coupe body.

Left: The Julian sport coupe: 1927

The radial, six-cylinder engine was set horizontally at the rear, as in the North-Lucas car. The cylinders were set 120 degrees apart. It appears to have been a four-stroke engine so it is unclear how the cylinder firing order could be arranged with an even number of cylinders. The crankcase was aluminum. Bore and stroke were 3.375 x 5.0 inches giving a displacement of 268.4 cu-in. (4398 cc) The power output was said to be 60 HP at 2500 rpm. The compression ratio was a modest 4.8 to 1.

It is currently unclear how the cooling air got into the engine compartment. Presumably it exited downwards.

More information can be found at The Old Motor.

Left: The Julian sport coupe: 1927

This contemporary image, sadly of poor quality, shows the rear engine and part of the chassis. Note part of the exhaust manifold leading into the cylindrical silencer.


Left: The Rohrbach concept put a radial engine in each wheel: Modern Mechanix 1931

There are, I suggest, some obvious problems here. There are two engines to go wrong and I suspect driving on one engine is not going to be feasible. The engines are unsprung weight and will cause some serious handling problems. The spark-plugs and ignition system are partly shielded from the elements by a casing but I suggest they are not well placed for ventilation, though the ignition etc may be kept dry.

There is the obvious problem of feeding the petrol supply, and the controls for throttle, clutch and gearbox, through a rotating bearing. It would be interesting if the two gearboxes got out of sync.

In short, this is a daft idea. However that never stopped magazines like Modern Mechanix publishing them. And why not? They have a certain entertainment value.

From Modern Mechanix May 1931, p84


Left: The Trossi-Monaco racing car: 1934

Count Carlo Felice Trossi was both a racing driver and a car constructor. As a racing driver he raced for Alfa Romeo, Mercedes-Benz, and briefly for Maserati. He won the 1947 Italian Grand Prix and the 1948 Swiss Grand Prix- but not in the car shown here.

The project was begun by engineer Agusto Monaco; he persuaded Fiat to test the engine at their Lingoto plant, but its poor performance and reliability led to Fiat withdrawing their support. Agusto then persuaded Count Trossi that the project was worthwhile, and this remarkable radial-engined car was built in Trossi's ancestral castle at Gaglianico, outside Biella in Northern Italy. It was designed to meet the 1934 Grand Prix formula.

The car looked very much like an aeroplane engine nacelle with the propellor missing, and created a sensation when it was unveiled. The engine was a two-stroke design with sixteen cylinders, arranged in pairs with one cylinder behind the other; each pair had twin pistons but a shared combustion space and single spark-plug. Its capacity was 3.982 litres. In a bay behind the engine were two M160 Zoller superchargers drawing from two Zenith carburettors.

The output of this amazing engine was claimed to be 250 BHP at 6000 rpm, which sounds impressive until you compare other contemporary racing cars such as the 3.8 litre Alfa-Romeo, (305 BHP) the 5-litre Auto-Union (375 BHP) and the 4-litre Mercedes. (430 BHP) The 1934 Grand Prix formula introduced a maximum weight limit of 750 kg, but there was still no limit on engine capacity; that was not introduced until 1938.

The Trossi-Monaco racing car is in the Museo dell’Automobile, Turin.

Left: The Trossi-Monaco racing car under test in 1934

The car had a front/back weight distribution of 75:25, because of the massive engine mounted forward of the front wheels, and must have been interesting to drive.

Note that here the Townend ring around the engine is not in place; possibly this was a attempt to improve the cooling. Normally a Townend ring manages both to reduce drag and improve air cooling, but here it does not seem to have helped.

Tests showed that engine was very prone to overheating; the exhaust manifolds masking the cylinders would not have helped. It also destroyed spark plugs rapidly. The car was clearly not race-worthy, and it never appeared at a Grand Prix race.

Left: The Trossi-Monaco racing car under test in 1934

With the Townend ring removed.

Left: Count Carlo Trossi at the 1934 Grand Prix

Carlo Trossi is pictured looking thoughtful at the 3rd June 1934 Grand Prix at Montreux, Switzerland.


Left: The Guidobaldi car: 1956

This racing car designed by Francois Guidobaldi was principally built to demonstrate a suspenson system that caused the chassis to lean into bends rather than follow the dictates of centrifugal force.

The car is currently in the private collection of David Humbert, who has had it completely restored.

Left: The radial engine of the Guidobaldi car: 1956

The Guidobaldi suspension system required the centre-of-gravity of the car to as low as possible, so a radial engine with its flat format was chosen. It was mounted at the rear of the car.

Guidobaldi designed the engine himself, coming up with a two-stroke, dual ignition, twin supercharged, air-cooled, 8-cylinder radial engine. Its capacity was 1500cc and so met the contemporary Grand Prix regulations which permitted either 4500cc unsupercharged or 1500cc supercharged engines. Fed by double Roots superchargers (originally from a Bugatti) the engine produced 180 HP at 6500 rpm.

The car was never raced.

Left: The radial engine of the Guidobaldi car: 1956

Just above the engine can be seen the distributor, with skew-gear drive from the crankshaft.

In the foreground are the two Roots superchargers. It is not currently clear how they were driven.

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