Interserie Chaparral 2J

The most unusual Chaparral was the 2J. On the chassis' sides bottom edges were articulated plastic skirts that sealed against the ground (a technology that would later appear in Formula One). At the rear of the 2J were housed two fans (sourced from a military tank engine) driven by a single two stroke twin cylinder engine. The car had a "skirt" made of Lexan extending to the ground on both sides, laterally on the back of the car, and laterally from just aft of the front wheels. It was integrated with the suspension system so the bottom of the skirt would maintain a distance of one inch from the ground regardless of G forces or anomalies in the road surface, thereby providing a zone within which the fans could create a partial vacuum which would provide a downforce on the order of 1.25–1.50 G of the car fully loaded (fuel, oil, coolant). This gave the car tremendous gripping power and enabled greater maneuverability at all speeds. Since it created the same levels of low pressure under the car at all speeds, down-force did not decrease at lower speeds. With other aerodynamic devices, down-force decreases as the car slows down or achieves too much of a slip angle, both of which were not problems for the "sucker car".

The 2J competed in the Can-Am series and qualified at least two seconds quicker than the next fastest car, but was not a success as it was plagued with mechanical problems. It ran for only one racing season, in 1970, after which it was outlawed by the Sports Car Club of America (SCCA). Although originally approved by the SCCA, they succumbed to pressure from other teams, McLaren in particular, who argued that the fans constituted "movable aerodynamic devices", outlawed by the international sanctioning body, the FIA, a rule first applied against the 2E's adjustable wing. There were also complaints from other drivers saying that whenever they drove behind it the fans would throw stones at their cars. McLaren argued that if the 2J were not outlawed, it would likely kill the Can-Am series by totally dominating it — something McLaren had been doing since 1967. A similar suction fan was used in Formula One eight years later on the Brabham BT46B, which won the 1978 Swedish Grand Prix, but Brabham reverted to the non-fan BT46 soon afterwards due to complaints from other teams that the car violated the rules. The car was found to be within technical specifications allowing the victory to remain.