Alloy Jaguar XK120 Roadster
Overview: The build of our first alloy XK120 racer was quite particular. Car #1 was built as a tribute to the famous period racing car of the early 1950’s, the Flag Blue metallic XK120 roadster LXO126 as raced by the legendary Scottish race team, Ecurie Ecosse. We wanted the car to look very much the same and wanted to include a lot of the distinguishing features that add to the charm of the car, without being tempted to modernise or upgrade the car too much. We built a very strong engine but one that is easy to drive and live with and one that looked period correct under the bonnet.
Basically, a very high quality, lighter, more powerful version of the car from the day that looked just like it!
Chassis: An original XK120 convertible chassis was restored, mounting for XK140 telescopic shocks added and then it was painted satin black two pack. We have brand new chassis available for subsequent cars to be built.
Body: The body is an all new hand made from aluminium, but in the shape and form of a steel bodied XK120 (as opposed to the early factory aluminium bodied XK120 roadsters that were alloy skinned over a wood ash frame). Deviations from standard include removal of the battery boxes behind the seats and deletion of the bumper bars, rear number plate plinth and fixed windscreens.
Correct period aero screens with period wind deflectors are fitted, a new chrome grille, new taillight assemblies and correct new tripod XK120 headlamps.
The body is finished in the correct Ecurie Ecosse Scottish race team colour of Flag Blue metallic.
This car is an XK120, but we can also build a car based on an XK140 if desired.
Engine: The engine bottom end is a 3.8 unit originally from a MKII but is fitted with the correct XK120 sump. It features custom length (longer than standard) Arrow conrods and short custom JE forged pistons with total seal rings. Compression ratio is 10.5:1. A late XJ Jaguar oil pump is used, mated to a remade larger version of the XK120 oil pickup to suit the sump. The whole bottom end has been balanced. ARP cylinder head studs and nuts are used.
We didn’t want to see a late (E Type) cylinder head or triple carburettors as I wanted the under bonnet to look a lot like the Ecurie Ecossie car. We used a correct early XK120/MKVII A port cylinder head of the type used on the Ecurie Ecossie car, an XK inlet manifold and new sandcast 2 inch SU carburettors. The head was CNC ported and larger stainless steel 1 7/8 inlet and 1 5/8 exhaust valves were fitted. New hardened valve seats, lightweight followers and valve retainers were fitted. Custom billet Kelford cams were fitted with matched valve springs. The inlet manifold was port matched to the cylinder head and to the 2 inch carburettors. AFM gaskets are used throughout the engine and a Cometic head gasket is fitted. A new alloy bodied water pump is fitted and a 123 electronic ignition system (with adjustable advance curve) and an MSD ignition amplifier are fitted.
The engine produces maximums of 285hp at 5900rpm and 283 ft/lbs of torque at 4200 rpm.
Different engine configurations and specifications are of course available.
Gearbox: Fitted is a brand-new alloy cased gearbox specifically designed and cast to suit Jaguar 6 cylinder engines and transmission tunnels. The gearbox uses the world renowned MT75 gearset as used in Ford Cosworth engineered cars and the ratios are almost identical to the standard gearbox ratios.
An E Type bellhousing which allows the use of a hydraulic clutch. The flywheel is a new alloy E Type and the clutch is a 9.5in AP Racing diaphragm clutch. Apart from the overdrive 5th gear, lighter weight and slick shifting, the other bid advantage of using this gearbox as opposed to the original Moss gearbox, is the use of a hydraulic clutch.
A new heavy duty tailshaft was fabricated to suit and the clutch hydraulics are in the form of a Tilton master cylinder, E Type slave cylinder and a braided line.
5 speed Original Moss
1st 3.31:1 3.375:1
2nd 2.08:1 1.982:1
3rd 1.36:1 1.367:1
4th 1:1 1:1
5th 0.763:1 na
Reverse 3.26:1 3.375:1
Final Drive: An XK150 differential assembly was used as it was Limited Slip and gave provision for the use of period disc brakes if ever fitted. The differential was fully rebuilt with a new 3.54 crown wheel and pinion fitted.
Suspension: Original XK120 suspension arms and stub axle carriers were used with the suspension upgraded with new larger diameter 1.057” (standard 0.930”, SE 1.000”) front torsion bars and new larger diameter 0.875” (standard 0.6875) front sway bar. Poly bushes are used throughout. New stainless-steel stub axles are fitted. Externally adjustable GAZ front shock absorbers are fitted.
New uprated rear springs leaves were made and fitted and the rear shock absorber system converted from the original lever arm to XK140 telescopic shock absorbers (adjustable KONI shocks used).
Steering: An original right-hand drive XK120 steering box is used with all correct right-hand drive steering link components, all totally reconditioned. Adjustable tie rods are fitted. An exact replica C Type steering wheel is fitted.
In the case of building an XK140, a correct XK140 steering rack would be used.
Brakes/wheels/tyres: Fosseway front disc brake kit is fitted along with late XK120 self-adjusting drum brakes with all new components at the rear. The front brake pads are EBC Ultimax 2 and the rear brake linings have been relined with a race compound. The hydraulics are controlled from the custom floor mounted pedal box using two Tilton master cylinders and an adjustable brake bias. Braided brake hoses are fitted.
The five roadwheels are original XK120 and drilled to remove brake heat as was a period modification performed back in the day, just like on LXO126, painted silver. The tyres are Vredestein 185HR15 radials.
Brake variations can be catered for including 4 wheel disc brakes and different wheel options can also be catered for including splined Dunlop replica wheels or wire wheels.
Cooling/Fuel/Exhaust/Electrics: An Alicool (UK) aluminium radiator is fitted with an integrated electric thermo fan, controlled by a Davies Craig adjustable fan controller (with LED temperature display).
A new aluminium fuel tank is installed with a period correct external quick fill fuel filler. A new, correct, negative earth square bodied SU fuel pump is fitted with braided lines from tank to carburettors. Fuel requirement is minimum 98 PULP.
The exhaust is full stainless mandrel bent Classic Fabs (Scotland) single to twin SE style system.
A new cotton braided writing loom is installed. The car has been converted to negative earth and a sealed Odyssey battery installed in the boot. A Dyna Lite alternator (generator lookalike) is fitted with a dummy period looking regulator with internal full system fusing. A gear reduction starter motor is also fitted. All new dash switches have been fitted and the original early XK120 instruments restored. The tachometer has been converted internally to operate electrically instead of by cable. A modern brake and reverse light switch have been incorporated into the brake pedal and gear lever assembly, respectively.
Interior: The interior is finished in black leather to replicate LXO126. The seats are replica C Type bucket seats trimmed as per the factory optional XK bucket seats. A custom designed and made stainless steel pedal box assembly is fitted to give vastly improved control of the brake, clutch and throttle pedals whilst increasing legroom. The interior is essentially trimmed as per a standard XK120 roadster.
General and Technical Specifications and Comparisons
Dimensions: #1 XK120 special Standard XK120 C Type
Wheelbase 2,590 mm 2,590 mm 2,438 mm
Track Front 1,308 mm 1,308 mm 1,295 mm
Track Rear 1,283 mm 1,283 mm 1,295 mm
Overall Width 1,580 mm 1,580 mm 1,638 mm
Overall Length 4,180 mm 4,410 mm 3,998 mm
Overall Height 1,120 mm 1,295 mm 1,080 mm
Ride height* 210 mm 285 mm 270 mm
Ground clearance 100 mm 181mm 140 mm
Kerb Weight** 1005 kg 1,305 kg 985 kg
Fuel tank capacity 68 litres 68 litres 177.3 litres
Power 285hp at 5900rpm 190hp at 5400 rpm 205hp at 5800 rpm
Torque 283 ft/lbs at 4200 rpm 195 ft/lbs at 2500 rpm 220 ft/lbs at 3900 rpm
0-60 MPH yet to test 8.4 sec 8.1 sec
Top speed (3.54 ratio) yet to test! 120 mph 145 mph
*measured between the ground and the centre of the front chassis crossmember
** with all fluids and 20 litres of fuel