Chris Isaacs race cars

Unique vision - innovative design - quality fabrication

Paul is building his MK 1 Zephyr with the engine, transmission and suspension from a late-model supercharged Jaguar XJR - the motor is based on the Ford 'Modular' quad-cam unit - and CIRC have been selected to build the spaceframe chassis to take all this running gear.  This street- and occasional track day-car is to be a full four-seater, with no roll cage, so the chassis design must be stiff enough to withstand hard use without flexing, whilst being unobtrusive enough to allow for all passengers.

Initial work has seen the body, motor and cast aluminium uprights fixed to the jig, and the first few tubes of what is to be a tubular backbone-style chassis laid down.  Also shown here in the lower RH photo is a body mounting point at the end of the main centre crossmember.

Most of the front chassis sides are constructed, and the air-ride dampers are fitted.  The front crossmember is fabricated from flat sheet - the steering rack and engine mounts will also go on here.

This fabricated brace across the top of the engine bolts into place using the same bracketry holding the inner pickup points of the fabricated top A-arms (these brackets are yet to be gussetted).  Newly fabricated top arms were necessary due to the smaller size of the Zephyr relative to the Jaguar donor car, meaning that these arms needed to be 45mm shorter from inner pickup to outer ball joint in order to clear the valve covers.  However, careful plotting of suspension geometry has retained good wheel angles in roll, sufficient anti-dive and good control of the dynamic roll centre.

The LH photo shows another view of the chassis brace and top A-arm.  Raked-back angle on the mounting points is a sign of significant anti-dive geometry, in this case mirroring that used on the original Jaguar.
The RH photo shows an overview of the front chassis structure.  The frontmost section of this, which will eventually mount the radiators and front anti-roll bar, unbolts via the four fixing points at each corner, making engine removal much more straightforward than may first appear!

The central backbone of the chassis is being filled in now, and more tubing is being added to the rear section.  More triangulation is still needed here to give a really stiff structure.  The differential is mounted on polyurethane bushes, one at front and two at rear.  The rear diff mount unbolts from the chassis so the diff can be removed towards the rear of the car, tubes running underneath it stopping it from exiting downwards.

The chassis tubes are now essentially complete.  The rear A-arms have also been mounted, as have the rear air shocks.

Some shots of the finished chassis.  The whole structure exhibits very good stiffness plus decent suspension geometry, and should give a nice-handling package in the completed car.  Incidentally, the rear suspension shots also show the Jaguar electronic handbrake motor, mounted above the diff.

Most of the tinwork pieces have now been completed, as have the seat mounts.  A rear seat will eventually be used in this car to make a full four-seater.

This tricky little panel is fabricated from several pieces of sheet steel...
... And fits up behind the dash to seal against the chassis-mounted master cylinder bracket.

The front anti-roll bar is now installed, and the CIRC fabricated arms bolt up to the original Jag drop links at the rear of the track control arm.

The front panels are now mounted, showing the close wheel-to-arch tolerance a la circuit racing saloon.  The mountings for the front valance also incorporate the mounts for some of the car's five radiators.  There are three here... engine coolant, air conditioning, and intercooler for the supercharger.  The other two - the engine and gearbox oil coolers - will go elsewhere.  Things are getting tight now!

The car about to leave the shop.  The subtle outer appearance belies the amount of work that has gone on underneath.  Should make a nice street/track day car when completed.