Car Features

Historic X-8 Engines


The ‘X’ configuration attracted a number of engine designers, including – most notably – Henry Ford. We’ve chosen X-8 initiatives with some automotive applications for this report, but all of them were fated to fail.


It’s not always remembered that, back in the 1900-1920s period, early engine makers were designing power plants for stationary, automotive, marine and aircraft applications. The attraction of having a single engine configuration that could satisfy all these different needs was obvious, in terms of economies of scale.

By 1920, Henry Ford was actively pursuing a successor engine to the in-line, water-cooled, four-cylinder that had been powering the Model T since 1906. In the early 1920s there were around 60 different experimental engines being investigated at Ford, but Henry’s favourite was the X8.

Interestingly, at the same time, Ford had invested in the Stout Metal Airplane Company that was using Curtiss-Wright air-cooled, radial engines. That investment grew to full ownership by Ford in 1925 and the Ford Trimotor aircraft saw production until 1933. Could that 1920 investment have influenced Henry’s air-cooled, radially-disposed-cylinder thinking?


Ford Archive


The Ford X-8 was essentially two 90-degree V-4s mounted in side-to side orientation and mated to a common crankshaft. Two opposed crank journals shared two sets of four connecting rods and two crankcase-mounted camshafts operated the valves, via short pushrods.

The original, patented-design engine was a 108 cubic-inch, side-valve, L-head design, with wedge-shaped combustion chambers above flat-top pistons and side-mounted spark plugs. However, there were also air-cooled and water-cooled L-heads as well as at least one aluminium, water-cooled, overhead-camshaft version. 


Ford Archive


The 1924 prototype X-8s were very compact, measuring only 17 inches in diameter and 14 inches front to back. However, the road-test engines weren’t trialled in a Model T, but in an Oldsmobile that Henry and his test drivers drove, on and off, for around a year.

Precise details of the test program have been lost over the intervening years, but the X-8 is known to have had problems with road debris impacting the bottom cylinders and the lower spark plugs also suffered from excessive fouling.

It’s not recorded if the Ford X-8s suffered from hydraulic locking, caused by oil or fuel draining into the lower cylinders after engine shut-down. However, this was a well-known problem with radial and rotary aircraft engines, which is why a pilot or ground staff always manually rotated the propeller before closing the ignition switches to fire up the engine. It was much better to discover engine hydraulic lock-up with only hand pressure, rather than combustion pressure that could destroy the engine.

Whatever Ford and his engineers discovered, the X-8 project was shelved and the Model T car was replaced in 1927 by the Model A, powered by an utterly conventional, water-cooled, in-line, four-cylinder engine. However, in the background, Henry Ford and some hand picked engineers were busy, secretly developing the ground-breaking, mass-produced flathead V8 that was launched in 1932.

Seven X-8 prototypes were initially stored and then four or more were disbursed around the USA. One is now on display at the Henry Ford Museum in Dearborn, Michigan. 

Ford Archive


At least one was stored at the Ford Greenfield Village museum, but apparently was mis-cataloged as a 1946 company project that was abandoned. It was among numerous engines designated for ‘house cleaning’ and was put up for sale at the 1982 Greenfield Village Fundraiser Auction, along with some old radial aeroplane engines. Eli Apolzon’s bid for the X-8 was successful and he onsold it, with the funds being donated to charity.



Leyland-Thomas X-8


John Godfrey Parry Thomas was a British engineer and was widely known as Parry Thomas. During World War I, Thomas was a member of the Munitions Invention Board and was employed as the chief engineer at Leyland Motors in 1917, to help the firm develop an aircraft engine.

Assisted by Fred Sumner and Reid Railton, Thomas’ engine design was an X-8 with cylinder banks spaced at 90 degrees. Each cylinder bank consisted of two paired cylinders. The cylinder banks were cast integrally with the aluminium crankcase and nickel-chrome cylinder wet liners and were heat-shrunk into the cylinder banks. An aluminium cylinder head was attached to each cylinder bank by eight bolts.




A single overhead camshaft operated the two intake and two exhaust valves for each cylinder. Each camshaft was driven by a vertical shaft at the rear of the engine.

The X-8 engine produced 300bhp (224kW) at 2500 rpm and weighed only 500lb (227kg) that was remarkably light for a 16.7-litre engine. However, during early testing, the X-8 engine’s lightly-built crankcase deformed and closed up the crankshaft bearing clearance, resulting in the engine seizing after a few hours of running.

When World War I ended on 11 November 1918, further work on the Thomas X-8 engine was abandoned, but a number of features from the aircraft engine were later used on the Leyland automotive straight-eight engine, developed in 1920. 

Thomas went on to become a legend at the Brooklands Raceway, campaigning one of the first aero-engined Land Speed Record (LSR) monster cars and set a flying-mile (1.6km) LSR of 170.624mph (274.593km/h) on 28 April 1926. Thomas tragically died in a crash attempting another LSR on 3 March 1927.



Hoffman X-8 


1935 Hoffman X-8 – Geoff Hacker


At the 2012 Pebble Beach Concours, there were the usual wonderful oddballs and one such car was the 1935 Hoffman X-8, owned by Myron Vernis of Akron, Ohio, 

The Hoffman X-8 was designed and built by Detroit-based engineer Roscoe Hoffman, who worked for Packard, Studebaker and Ford from the 1910s until the 1950s.  

One of our sources, Citroënvie, theorised that the X-8 was developed by Hoffman under contract to the Fisher Brothers in the early 1930s, prior to that bodybuilder’s purchase by General Motors. Fisher had been angling to buy Hudson and the Hoffman design was the base for intended small-Hudson, rear-engine developments.

The design was no ‘concept car’, because it had production-ready features, including symmetrical front and rear doors.

The Hoffman X-8 was revolutionary in using the monocoque, load-bearing bodywork design, developed by Budd Automotive in the USA. (Citroën’s 1934 front-wheel-drive Traction Avant also used Budd-designed monocoque construction.) Hoffman was a pioneer of the US streamlining movement and his X-8 shape was very streamlined, for 1935.  



Interestingly, Myron Vernis obtained photos of the Hoffman prototype being built around wooden bucks. A very interested spectator in one of the photos looks like Joseph Ledwinka (a distant relative of Tatra’s genius designer, Hans Ledwinka). Joseph was involved in the design of the streamlined Chrysler Airflow.


Geoff Hacker


The Hoffman X-8 was a five-seater and weighed 1.4 tonnes unladen. Engine output was a very competitive 75bhp, from a displacement of 170 cubic inches (2.8 litres).

The engine was rear-mounted, in front of a radiator and the transmission was mounted beneath and behind the radiator. The cooling fan was driven from a transmission output shaft and sucked air through the radiator and blew it out through rear-bonnet louvres.


Geoff Hacker


Because the Fisher-Hudson takeover never happened, the prototype was the only Hoffman ever produced and he kept it until 1961, when he gave it to industrial designer Brooks Stevens.  The X-8 remained with the Stevens’ family until 2010, when it was acquired by Myron Vernis.


Geoff Hacker


The Hoffman X-8 was a one-off and its precise mechanical details have been lost. Jay Leno did an excellent video interview with Myron Vernis, during which he suggested that the three-speed manual transmission looked like it may have been adapted from the transmission of the Cord L-29.



General Motors X 250



A liquid-cooled, supercharged, two-stroke engine, this 1940 General Motors engine was a very unusual design, incorporating four cylinder blocks, each containing two cylinder bores, sharing a common combustion chamber. 

From a displacement of 252 cubic inches (4.1 litres), it produced 225bhp (168kW) at 2500rpm, yet weighed only 125kg. 

At least one application was powering a radio-controlled target aircraft and it also powered an Oldsmobile Eight car. 

A 1942 engineering report written by GM’s Research Laboratories, led at the time by highly regarded director Charles F Kettering, stated that the engine had excellent power from displacement and power to weight ratios, low fuel consumption and very low vibration characteristics.

However, it never went into production and the surviving engine is in the care of the US National Air and Space Museum.

If we come across more X-engine initiatives, we’ll add them to this article. in the meantime, here’s a possible packaging issue that racing radial and X-engines might have…


1935 Monaco-Trossi – BrianSnelson


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