The Allard J2X Story

By Michael J. Fuller

Some of the most advanced sports prototypes ever designed were born out of the 3.5 liter Group C Championship.  The two short years of that series saw some of the largest evolutionary jumps in prototype design, brought about by competition among car manufacturers such as Jaguar, Peugeot, and Toyota. 

It was into this environment that the independently designed Allard J2X was born, to much anticipation. By 1991, mainstream sports car design bore little resemblance to the Porsche 956s and Lancia LC2s that first debuted some 10 years earlier.  The Allard J2X suddenly accelerated the pace of thinking at a time when the development graph was already quite steep.

But the Allard was a veritable flash in the pan and followed the fate of many racecars by failing to realize its potential.  So what happened to this car and who was behind it?

Chris Humberstone was a designer with a flair for tackling and managing complex engineering projects.  Over the years he had worked at various racing teams and manufacturers, accumulating an interesting resume; Beatrice / Force F1, Benetton, and Brun Technics. In the late 80s Humberstone approached Alan Allard, the son of Sidney Allard, about licensing the family name for a future road car project. Though delayed a number of years, in the early 90s Humberstone finally formed Allard Holdings with the intent of moving forward.  The Allard name would imply credibility and history to the effort and open doors that may have otherwise remained closed. Costas Los and Jean-Louis Ricci would eventually come on board with investment capital, also bringing along their own racing contacts, besides the money to help move the project ahead.

Costas Los’ professional background was in business, property, and shipping. Given his professional racing resume, that can almost be considered his side career. Los has driven everything from the ubiquitous Porsche 962 to the Aston Martin AMR-1 and the Gebhardt Audi. 

“Right after my season in Japan, I took a year off and ran into Jean-Louis Ricci who persuaded me to get involved in the Allard project”, says Los. He, along with Ricci, put up a percentage of the initial startup monies. Los would then spend the next 24 months concentrating on tracking down additional funding as well as an interested manufacturer. 

The Allard team’s intent was to build a customer racecar and also have a road car tie-in, an Allard designed supercar. The Allard J2 supercar was to have been loosely based upon the J2X Group C chassis, and use a detuned Allard-badged Cosworth DFR. Though the J2 was a future project to be completed after the J2X was successfully on the track, two Lexus LS400s were modified by Allard (mainly styling, aerodynamics, and interior) and used as lures for potential manufacturer backing for the J2X. The LS400s were presented to Toyota in hopes that they would be interested in the Allard tie-in, to sell a low-volume exclusive, the Allard LS400. In fact Toyota did show interest, but confusion amongst the Allard partners led to them being unable to present a clear marketing proposal. Toyota quickly lost interest.

In the meantime, Humberstone began to bring together a group of young, enthusiastic, if somewhat inexperienced, designers and engineers. Humberstone approached Hayden Burvill and began forming the core of the design staff, starting in late 1990. The Australian Burvill became Chief Designer for the J2X: his background was Industrial Design. Burvill: “ID people bring depth of conceptualization, relative freedom from initial technical or material hurdles, a can-do attitude and confidence towards the creation of ground breaking solutions. Ultimately the real strength of the J2X project was the ability to move forward without hefty pre-conceptions.” 

Burvill’s ID background would play from strength to strength, given the wide-open nature of the Allard’s design brief. 

John Iley, the J2X’s aerodynamicist, joined Allard from Brun Technics in early ‘91. Iley had a hand in the aerodynamic development of the Brun C91 when he was fresh out of university. “During my final year (of university) I spent a large proportion of my time doing wind tunnel testing and data analysis of a sports prototype. I was lucky that Chris Humberstone saw this work. At that stage he was in charge of Brun Technics design in England and he offered me my first job. I joined as a designer, with emphasis on using my recent aerodynamic studies on their latest 3.5 litre car.” Humberstone soon left Brun to pursue the Allard project and contacted Iley as things developed.

Both Burvill and Iley were relatively inexperienced when considering the task at hand, but, as Burvill puts it, “Chris Humberstone would not have been able to create this project in the way we did if he had used a more experienced or named designer. When you consider the time period and the J2X peers, having a highly conceptual novice was kind of prerequisite to achieve what we did with the Allard.”

Not wasting any time, conceptualization for the J2X began in the late months of 1990. “We had seen people do maximum cross section for chassis stiffness (Brun C91) and we knew about the XJR-14 being very low profile. Our approach was to optimize the package to allow maximum volumes for investigating the aero solution,” says Burvill. John Iley adds, “you always look for targets, areas for improvement, areas of strength with existing designs, ways to get the most from the category’s regulations...there is also the difficulty of striking the right balance during development of very original new concepts, versus iterative steps”. 

The primary goal was minimal frontal area, and the J2X’s radical look was the result. 1/10 scale study models were built to evaluate ideas (1/3 scale model, above), with Burvill and Humberstone contributing; Iley joined the project a few months later. 

What began to emerge combined the best of all elements - narrow tub (above) and bubble canopy, detached front fenders, front wing, and very low profile rear bodywork. Two 1/3 scale wind tunnel model spines were used to evaluate as many ideas as possible. It would have been preferred to use the Imperial College wind tunnel in London, but McLaren was the favored customer and there wasn’t any tunnel time available for the Allard group. Clearly the J2X concepts were unlike anything that was racing, and there was some question if they would produce results in the wind tunnel. The MIRA wind tunnel in Warwickshire, England, was chosen and testing began in earnest. 

Iley: “We tested in regular short and intensive three-day test sessions, starting from the very first test with the radical minimal layout, to see if we could get it to work. It showed sufficient promise to persevere, with gradual improvements being made test by test, to produce a strong, distinctive and legal aero platform.”

The quest for front-end downforce was nothing new in a closed bodied prototype.  Sports cars have historically been hampered by a lack of front grip.  The design goal has always been to dial in as much front grip as possible to reduce or eliminate the car’s understeer without affecting airflow to the rear wing.  Splitters had been the predominant device to increase front load through out the Group C and GTP era and were somewhat effective if limited in their scope of adjustment.  But even early on front wings had been tried on sports cars with the results being less than satisfactory.  The March GTPs actually ran an adjustable wing element between the “Lobster Claws” and below the radiator.  The Grid S1 even further accentuated the idea by mounting a front wing, again between the front fenders, but well ahead of the intake ducting.  And various Porsche 962 teams mounted ungainly wings on the noses of their cars, again in the search for downforce.  The concept had been revived most recently by the Jaguar XJR-14 and was also subsequently used on the rival Peugeot 905 Evo 1.  But typically the front wing element spoiled the airflow to the rear wing.  Ironically this produced the desired result, a forward balance shift, but was undeniably detrimental to overall downforce, especially rear.  The J2X’s complex front wing, with its secondary flaps situated between the front pontoon fenders, was squarely aimed at eliminating the historical sportscar understeer condition.

We could generate up to 43% front aero balance if we wanted to.  This was a combination of having clean airflow between the chassis and the front wheels and careful treatment ahead of the wheels,” says Iley.  Burvill: “The front wing definitely worked in isolation. The impressive L/D figure would not have been achievable otherwise. What you cannot see is some quite sophisticated air management under the nose.” The J2X featured a raised front nose and tub that the front wing drooped off of.  Burvill admits to being influenced by the Tyrrell 019 F1 car when it came to the drooped or anhederal front wing, “It seemed logical to increase the air gap under the nose to reduce the volume change under the nose with pitch and ride height change, the Tyrrell offered the first working version of that.“  The raised nose and subsequent air management aft of the front wing allowed for air to flow onto the top surfaces of the floor just behind the front wheels.  Burvill continues: “This air was then managed rearward over the extremely low profile rear deck. This was to make the rear wing work harder, not suffer.”

Additionally, the front wing flaps performed a rules compliance function by masking the suspension components, as seen from the front. John Iley says, “The launch version of the car, which was in a maximum downforce configuration, had probably about ten settings, the problem being to keep the suspension covered in elevation at the same time.” The rules function of the front wing flap did limit its amount of travel somewhat, in that at lower flap angles it would have been possible for suspension components to be seen (hence, rendering the car illegal), but within the practical range of flap angle vs. balance, it was not an immediate issue. 

Interestingly enough, additional front downforce could be dialed in by adjustments made at the rear of the car.  The lower element of the Allard’s twin-tier rear wing was found to be a powerful device to tune aerodynamic balance front and rear.  With the primary suction peak of the diffuser being forward in the underbody, any increase in flap angle of the lower wing at the rear of the car would increase overall downforce and in turn increase front downforce as well.

The pontoon fenders were perhaps the most unique element of the entire design and an integral part of the aerodynamics package.  Though surprisingly the Allard’s design didn’t evolve towards that solution, it started there: “Quite simply I shaped up the first version based on experience, we tested it, it worked great, we never discarded it”, says Burvill.   To cover their bases the Allard team did try a much more conventional front end but found it seriously lacking when compared to the direction they had initially headed in.  By encouraging airflow around the fenders instead of over them (simply by the nature of its planform shape) helped reduce top surface lift generation.  You’ll note that the Allard is streamlined in plan view, not elevation, to do just that; encourage air to go around and not over the bodywork.  There was also thought to be a functional benefit of the pontoon fenders in the case of a tire failure as damage would be limited to the pod and not the surrounding bodywork and replacement of the bodywork would therefore be easier.

Cooling airflow was surprisingly simple.  The radiators were contained within the pontoon fenders that enveloped the rear wheels, the radiators themselves just ahead of each rear wheels.  The plumbing for the radiators was short and routed from the radiators straight into the front end of the engine.  Cooling airflow was ducted in via openings in the leading edge of the rear pontoon fenders.  The heated exhaust flow was cleverly drawn out and exited the car into an area of low pressure located near the inboard vertical face of the rear fenders.  Given the proximity of the radiators to the tires there certainly would have been concerns of damage occurring to the radiators should a rear tire fail.

As mentioned, the achievement of the ultra low rear deck height of the Allard was driven by the desire to feed the rear wings with airflow as unobstructed as possible. Additionally, the exhaust gas was piped into the trailing edge of the tunnel exit, but for a purpose other than aerodynamic.  Iley: “As a rule I am not a supporter of such a system (exhaust activated diffuser) as it makes the car’s performance too throttle dependant, which does not provide the basis for a stable platform. However the location on the J2X Allard was far enough rearward that its effect was greatly reduced. The main drive to route the exhausts this way on J2X was just to achieve an incredibly low and tidy rear deck for the lower rear wing, not to utilize a blown diffuser principle.” Ultimately the designers were able to achieve a rear deck height only some 10 mm above the rear tunnel exit.  Given that the radiators exhaust flow was isolated from the engine bay, little airflow, if any, exhausted out the rear of the engine bay allowing for such a low rear deck.  

According to John Iley, the J2X developed approximately 5500 lbs. of downforce for 916 lbs. of drag at 150 mph (L/D 6.0:1). “Yes our loads were huge and what little correlation work we did to the tunnel numbers seemed to agree with them well.” Fifty-five hundred pounds equates to a theoretical 9778 lbs. of downforce at 200 mph. Peak downforce was achieved at a 35 mm front ride height and a 48 mm rear ride height, with good high ride height performance and low overall pitch sensitivity. With only some 560-580 horsepower on tap from its 3.5 liter Ford DFR, a low downforce package would have eventually been developed, though it was clear that a more powerful engine would have greatly benefited the project.

With such high aerodynamic downforce, a power steering system was also deemed a necessity, though never developed or installed. Eventually the front suspension would have required reworking to allow for the fitment of such a system so it became a future project. A simple active suspension system was installed for the J2X’s testing, though never optimized.

It was the anticipation of the car’s massive downforce that led to the design of full-length monocoque structure.  The monocoque structure incorporated a rear composite chassis that housed the gearbox.  The rear chassis was designed so that the gearbox could be swiveled within the structure to allow for easy change of the gear cluster. The entire tub, minus the gearbox sub structure, but including the FIA mandated steel roll over hoop, weighed around 85 kgs. The full-length tub allowed for the potential installation of various customer engines, which were anticipated to be used by IMSA competitors.  The underfloor in the area of the engine was part of the monocoque structure and thus added substantial stiffness to the rear end of the car as well as potentially allowing for the consideration of other, unstressed, engines for future installation, assuming they’d fit.

Burvill: “The chassis comprised a closed box section 100 mm wide on each side, running the full length of the footbox and sills. The roll hoop could not be fully integrated or made of anything but certified diameter and wall thickness steel, unless we had subjected the tub to a potentially destructive crash test. We had the roll hoop inspected and then bolted and bonded it into the chassis before the top section of the chassis was bonded - so it did become fully integrated.” 

Unfortunately the rear composite chassis turned out to be a potential liability, compromised by the use of an off the shelf gearbox (Leyton-March). According to Paul Burgess, detail designer engineer for the J2X’s rear chassis, the design was, “constrained by using an existing single seat gearbox with integral rocker and suspension mounts, it was complicated to mount and access the gearbox internals. A much neater solution would have been to design and build a separate and easily changed gearbox, without any suspension mounts on it.” Track testing would later bear out the need to rethink the gearbox housing, if not the need redesign it.

The J2X’s front suspension consisted of upper and lower A-arms mounting to steel fabricated uprights.  A pushrod attached to the lower A-arm and actuated a spring/damper that mounted to the monocoque.  At the rear the suspension was similar in layout with the spring/dampers located in the rear carbon sub structure, being easily accessible from a top opening.  The A-arms were mounted to aluminum brackets that then threaded into inserts in the carbon structure.

 A 3.5 liter Cosworth (Ford) DFR engine was chosen for the Allard given the commonality of the engine in Group C at the time.  Though it was actually intended that the first J2X be installed with a Small Block Chevy, but when a potential customer showed interest in a Group C version of the car, the 3.5 DFR went in.  The Small Block Chevy engine would have required a Hewland DGC gearbox to replace the Leyton-March sourced one, a task that would have been welcomed by the design staff given the problematic March gearbox.  Mazda and Porsche engines were considered and rejected given difficult packaging requirements even though potential customers in IMSA may have wanted those engines options.  Ryan Falconer had even been contacted about the use of a Big Block Chevy.  The Allard’s chassis, while appearing to lend itself to the installation of various engines with its full length monocoque (and the apparent ability to run structurally unstressed engines), in actuality was compromised by the tight packaging at the rear.

Interestingly enough, the entire Allard J2X was drawn by hand. Hayden Burvill again: “The car was drawn on a five meter drawing board, and all the body sections were faired by traditional lofting techniques. The pattern makers had a real challenge with some of the parts, particularly as the drawings were often quite Spartan and allowed for ‘PMB’, Pattern Makers Blend.”

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To Part II
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ęCopyright 2008, Michael J. Fuller