Lucas Fuel Injection

Fuel supply to the original 1966 XJ13 was managed by Lucas Mechanical Fuel Injection.

This system was retained by Jaguar when the car was rebuilt in 1972/73 and remains with it today. The heart of the system is the Lucas metering unit which sits in the "V" of the engine and distributes fuel to each of the 12 cylinders.

The following picture shows the unit in-situ in the car today:

Lucas Fuel Injection unit fitted to the "original" XJ13

The unit is belt-driven at half engine speed using a cog provided at the end of the distributor drive. The following picture shows the cog and mounting points on my engine (prototype engine No2) - just crying out to have a metering unit fitted!

Mounting point for Lucas Fuel Injection metering unit

This type of fuel system was "state of the art" in the 1960s and was fitted to many Ferrari and Maserati racing engines of the time. Finding an original unit proved to be very difficult. Although I actually succeeded in tracking down an original unit which the owner claimed had been removed from the original XJ13 during its rebuild in 1972, it turned out to be so badly damaged and corroded that renovation would not have been possible.

These units are manufactured to tolerances of less than one tenth of a thou and are absolutely critical to the efficient running of the engine. Bearing this in mind, I decided to commission a new unit - built to the original specification. I was fortunate enough to be able to make contact with one of the few engineers capable of carrying out such a task and I am now the proud owner of a brand new, original specification metering unit. It was pleasing to find that the skills to make the units are still available in the Midlands - not too far away from Coventry. These units are truly "works of art" and I look forward to the day when it can take pride of place atop my V12 prototype engine.

Newly-manufactured Lucas Fuel Injection Metering Unit.

Newly-manufactured Lucas Fuel Injection Metering Unit.

The Lucas petrol injection system has been outstandingly successful on high performance cars, particularly in the international racing field. During 1966-67 the first three places in almost every Grand Prix event were held by cars equipped with a Lucas petrol injection system.

1969 Lucas Ad.

A conventional carburettor is not required in the petrol injection system. Instead fuel is injected into each of the 12 air-intake ports by means of this high-pressure metering device.

Some of the more important advantages to be obtained from the use of petrol injection are:

• Reduced Fuel Consumption - A more economic use of fuel, because the quantity injected into the cylinders is closely regulated to suit the engine operating conditions.
• Smoother Running at Low Engine Speeds, and Better Acceleration - Engines fitted with fuel injection equipment accelerate quicker and have greater flexibility, particularly at low engine speeds.
• Increased Performance - A complicated manifold is not required, so that the air intake is greater than normal. This ensures improved volumetric efficiency and hence increased power.
• Cleaner Exhaust Emission - As there is almost complete combustion in the cylinders, the amount of unburnt hydrocarbons and carbon-monoxide is reduced. The result is ‘cleaner’ exhaust emission.

Original Lucas Ad.

The amount of fuel in each injection, and the frequency of the injections, is controlled by the metering distributor and mixture control unit. The mixture control unit regulates the amount of fuel in each injection, in accordance with the requirements of the engine. The function of the metering distributor is to inject fuel into each individual inlet by a system of shuttle-metering. The two component parts - the metering distributor and the mixture control unit - are a “matched” pair.

The metering distributor consists essentially of two parts; the rotor and the sleeve. The rotor has two radial ports, which lead to a centre bore containing a shuttle - which is movable between two stops (one fixed and the other adjustable). The sleeve has fuel inlet and outlet ports. The rotor fits inside the sleeve and is connected to, and driven by, the engine.

A critical component of the metering unit is the "fuel cam" - a lever which is connects the accelerator linkage to the metering unit and controls fuel supply to the engine as required. The following drawing shows the design of fuel cam as originally fitted to the XJ13.

Drawing used to manufacture original XJ13 fuel cam. Drawing produced by George Buck of Jaguar in 1966. © Jaguar Heritage.

The profile of this cam is absolutely critical to efficient running of the engine and a number of different profiles were tried out at different times during engine test-bed development.

The following extracts from a report by George Buck in April 1966 confirm the final fuel cam specification used when the engine was first installed in the XJ13:

Extract from George Buck April 1966 report. © Jaguar Heritage.

Extract from George Buck April 1966 report. © Jaguar Heritage.

Extract from George Buck April 1966 report. © Jaguar Heritage.

To be continued ....