Chris Isaacs race cars

Unique vision - innovative design - quality fabrication

MG enthusiast and former TAD crewman Jason commissioned CIRC to build his concept of the ultimate track and road MGB.  The spec includes a choice of inline 4 or V8 engines, both utilizing turbocharging, a choice of sequential 6 or 7 speed gearboxes, and CIRC designed and constructed independent suspension all round.  An important part of the packaging on this car will be to allow for some extensive aero aids under, around and over the bodyshell.

The standard, ebay-purchased MGB bodyshell was fixed to the chassis jig, then the front and rear wings cut away to trial-fit the intended wheels to the body.  The wheels are 11" and 12" x 19" OZ Ultraleggeras, with a choice of tyres - sticky road, slick, and wet.  Intended ground clearance at the sills is 3.75" rear and 3" front, with a full flat floor under the chassis running into a rear diffuser.

A preliminary line drawing was done to ascertain the basic visual appearance with the required dimensions.  The left-hand drawing is standard MGB, the right-hand one is the modifed version with 5" wheelbase stretch, 4" longer front wings, and raised rear quarters and front arches to gain sufficient suspension clearance.  There will also be a 6" per side track increase, which puts the wheelbase/track dimensions and ratios similar to a range of GT3 race cars. 
CIRC will eventually be responsible for creating the patterns for the fibreglass body panels for the car.


The first few tubes of the 4130 chrome moly spaceframe chassis are in place.  Also visible here are the new, bead-rolled inner sills under construction.  These are currently oversized and the final dimensions will be determined once the side aero panels are being made.

More chassis tubes going in...


... and more tubes going in!  Many of the triangulation tubes are 1" OD or less, in 0.058" and 0.049" chrome-moly, to keep the overall weight down whilst the design of the tube placements still gives a lot of torsional stiffness.


The billet aluminium diff housing takes 8.8" Ford internals and sends the drive out to custom  31 spline stub axles which in turn bolt up to Porsche CV joints - this setup will take the considerable power potential of the MGB.

The rear suspension is of a pushrod bellcrank design, and considerable care has been taken over the geometry to allow for adjustable anti-squat (note the multi-hole mounting bracket for the front leg of the lower A-arm) without altering the roll centre position either statically or dynamically.  This will give the driver predictable cornering with a choice of anti-squat positions to dial-in optimum acceleration out of the turns.  The bellcrank geometry gives rising-rate suspension (the springs and dampers get 'stiffer' at the wheel as the suspension compresses), the percentages of which are the same front and rear.

The diff unit is mounted at its rear by a tubular subframe bolted to the chassis, and at its front by an aluminium plate similar to a motor-plate.  These structures locate the billet diff unit in all planes, and make it a stressed part of the rear chassis.  The chassis mounts for the front plate are quite substantial as they will also mount the rear anti-roll bar.


The 'K' member under the gearbox is unboltable to enable the 'box to be dropped out from underneath the car.  This tube structure will also carry mounting points for both the 6 speed (4 cyl motor) and the 7 speed (V8) 'boxes.  The unit in the car is the sequential 7 speed, designed to take 700 ft/lb of torque and intended for use in GT racing Corvettes, Vipers and the like.


Lower front A-arms and their mounting points are under construction.


Most of the chassis tubes rearward of the front motor-plate are now installed.


The CIRC designed sheetmetal front uprights under construction.


The front suspension is taking shape.  The RH photo also shows the mountings for the front bellcrank pivot, just behind the front upper A-arm mount.  The angles of these pivots is precisely set so that the pushrod and damper will not exert any side loadings on the finished bellcrank.


The turbo mounts are under construction.  The V8 will run twin turbos, one on each side, and the inline 4 just the left side turbo.  Each turbo will have its own charge-cooler, so when using the 4 cylinder motor one side of the complete induction setup is removed.


The CIRC designed and constructed rear uprights have been fabricated and installed onto the jig along with our fabricated rear suspension A-arms.

The bespoke steering rack was put together by Titan, to our specs.  Ignore the straight-up angle of the pinion in these photos, the rack was loosely installed for picture-taking and will end up at a more usual angle once the column goes in!

The narrowness of the caged body and the bulk of the 7 speed sequential gearbox limited the space available for seats, and a pair of Kirkey circle-track seats with CIRC modifications proved to be the best option - these are shown mounted into the car.  Eventually they will be padded and trimmed.

The MGB's brakes have been supplied by HiSpec, and shown here are the front calipers mounted to the uprights.  These are their top-flight 8 pot calipers, running on 400mm vented discs - the rear end features their Monster 4 pot calipers with built-in handbrake mechanism, gripping 360mm discs...

... And here is the whole setup, including discs, wheels, and bellcrank suspension linkages.  Those aluminium bellcranks were designed by CIRC and CNC machined from 6082 billet by an engineering contact of Jason's.  The solid links in place of the coilovers will soon be replaced by a set of Penske 3-way adjustable dampers.

A view of the bare chassis just after welding.  There are a few more tubes to add, but those will wait until the exact positioning of some other components are finalized.

As mentioned earlier, CIRC will also be creating the patterns which will be used to take moulds for the lightweight carbon and fibreglass body panels.  These patterns will be constructed by using steel sheet to get the basic shape, finalised with body filler, then painted to a high-gloss finish for the moulding process to take place.  Here, the very early stages of creating the new body shape are under way.

The front wing profile is taking shape.  We are incoroporating both the front and rear bumpers, and also the MG radiator grille into the new body shapes, to keep some of the recognizable MG lineage in the car.

The MG will be using water-powered chargecooling for the turbos, and the only realistic place to mount the chargecooler radiators is in front of the rear wheels, with air fed to them through ducts in the rear wheelarch extensions.  In order to maximise the radiator area, we had to sweep the rear quarter-panel and the rear edge of the door inwards, and the new sill extension downwards, to give the biggest area possible.
Note here how we have preserved the factory swage-line in the new in-swept bodywork, so the original MG chrome trim can be reattached and curved to meet the new body shape.  The RH photo shows a template of a chargecooler radiator sized for 600hp fitted into the available space - one of these for the 4-cylinder motor, and one each side for the V8, should thus provide adequate intake cooling.

More details of the bodywork take shape.


There is still some fine detailing to be done, but the basic body shape is now laid out.


... From now on, all current project updates will appear instead on our Facebook page - please click on the photo to the left to go there!