1992-1993 Allard J2X

Image copyright and courtesy Martin Spetz
Text copyright Michael J. Fuller

The rear end is dominated by the tunnel exits and the striking nature of the ultra low rear deck.  Considering how the cooling airflow is routed through the car, effectively nothing exits out of the engine bay, the engine cover has been lowered as much as possible at its trailing edge and is mere millimeters above the trailing edge of the underfloor.  Ultimately, though, Burvill admits, "I am sure this area of the car was not as optimal as the nose and areas further forward."
The engine exhausts exit just at the trailing edge of the underfloor.
Allard J2XThe reasoning for exiting the engine exhaust into the underfloor was driven primarily by packaging.  With the ultra low engine deck height and the trailing edge of the underfloor a mere 10 mm or so lower than the engine cover, there was no room to shoot it out the rear of the car.  So the only option was to plumb the exhaust into the underfloor.  Naturally there was a aero benefit, but as John Iley mentioned,"As a rule I am not a supporter of such a system 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."

ęCopyright 2008, Michael J. Fuller