Home Can-Am at Laguna Seca Chaparral Racing : The Increbible Chaparral 2J


The Increbible Chaparral 2J

by Dick Rutherford

editor's note: This article appeared in the 1970 program guide for the Monterey Castrol GTX Grand Prix. It was reprinted from Corvette News.

The car you see on the next four pages is perhaps the most incredible race car ever designed and built. It's the new Chaparral 2J. It promises to revolutionize everyone's ideas about race cars. Unless, of course, some spoil sports get together and ban it.

The Chaparral 2J will generate more corning power and more braking power than any Group 7 car today. And unless othr Group 7 constructors follow suit, as they did with the wing, the Chaparral 2J should continue to enjoy its outstanding edge in vehicle design for longer than one season. And even if Hall's competitors come up with a similar car in 1971, they still won't have the benefit of Jim's testing and de-bugging.

The 2J is the result of Jim Hall's quest for a new race car — a vehicle project begun in the middle of the 1968 season. The goal was deceptively simple: Find an "outstanding edge" in vehicle design. The "outstanding edge" is a design that will circulate any given race car faster than the competition.

The search for the outstanding edge took Hall to novel spoilers and the celebrated wings. The main reason for the wing was to generate downforce. Some automotive writers wondered publicly in print why the wings were attached directly to the rear suspension rather than to the body. Hall wanted the downforce generated by the wing concentrated on the suspension for greater adhesion. With this effect, he reasoned, the car should be quicker through any given turn. When the winged and spoilered Chaparrals ran right, they were. Mechanical failures kept the winged beasties from proving the total worth of the spoiler concept, and the structural failures of competitors' wings let to their ban by the SCCA.

Wings and spoilers were one experiment with downforce. Both, unfortunately, have severe limitations and at best are only a compromise between aerodynamics and downforce. The downforce generated at slow speeds is, in actual practice, minimal.

Another area of exploration was fourwheel drive. It, too, was found wanting. As were other areas of engineering research. The goal was to provide measurably more downforce without affecting the aerodynamics and drag associated with wings and spoilers. Not just aminute increase in downforce; a whole huge hunk of improvement. Enough downforce to equal a minimum of 50% more vehicle weight, without the extra weight penatly. What Jim was seeking was the equivalent downforce of 1,000 or more extra pounds without adding any weight. Sounds impossible.

The reason for the added downforce was simple. To improve the tire adhesion. Not only in the corners, where the quickest way through is best, but on the straights where they accelerate and decelerate. Jim wanted to keep the car glued to the track. A simplistic solution would be to add 1,000 pounds to the gross vehicle weight. But who ever heard of a 2,500-pound Can-Am car? Or, more absurdly, a competitive fully loaded cement truck Can-Am entry? No, pure weight piled and heaped on downforce all right, but when you try the first time to turn . . . or stop . . . it's all over.

In search of elusive downfoce, previous Chaparrals have sprouted front and rear spoilers, diviing planes forward on the fenders, front fender vents over the tires, movable rear spoilers, radiator air exits and fabled wing. All of these experiments resulted in only small amounts of downforce.

Sometimes during the thinking process in 1968 the idea jelled about a ground effects vehicle, only in reverse. Most people know GEV's will hover on a cushion of air and skim over land or water. What would happen if the fans were reversed so that instead of hovering, it clung? Novel. New. Untried. Off to the computer to see what design parameters were involved. Programming. Reprogramming. An explosion of arithmetic disgorged from the computer to give Chaparral cars what they wanted to know. Jim Hall, his chief vehicle engineer Don Gates, the talented crew have created a car that clings, literally, with huge suction fans.

The 2J has tremendous amounts of static downforce; more than 1,000 pounds of downforce on the tires plus the static vehicle weight. The effect is the same as adding 1,000 pounds of weight for the tire adhesion without carrying that extra weight with you during a race.


They made the rear portion of the car a gaint vacuum reservior. Shirts extended from the bodywork to the ground on all four sides, and cover the rear wheels, as the pictures show. In the rear, behind the enlarged ZL-1 Corvette engine which drives the car, are the two vane-axial fans powered by an additional small two-cycle engine. When the fans are running the evacute a large area under the car, and it's this suction which provides the incredible downforce. The skirts, made of General Electric Lexan, are articulated to move independently of each other to maintain the best possible seal between car and ground.

Testing proved the idea. You could almost say it works like sucking on a straw. Only instead of the 1/8" area inside a straw, imagine a 5,000 square-inch straw. If you could reduce the pressure inside the Chaparral "straw" by only .18 PSI (that's point one-eight), you'd get about 900 pounds static downforce working on the 2J. And that 900 pounds of downforce created by the suction works whether the car is standing still or hurtling down a long straight. Add approximately 150 pounds of aerodynamic downforce created by the 2J's design at 120 mph and the net downforce effect exceeds 1,000 pounds, total. The downforce figures were calculated at Midland, Texas, 3,000 feet above sea level. At courses closer to sea level, like Watkins Glen, the net result should improve about six percent.

What's it like to drive? Well, it's different because the cornering forces are greater than any race car has ever generated. Jim Hall says this, "The 2J's major advantage is that it will corner faster on low-speed corners, the ones that are 30 to 90 mph in normal Can-am cars. these corners predominate on Can-Am tracks. It means you can leave the corner faster, with more speed, and carry that speed down the straight." Skid pad tests at the chaparral car's test pad show that the 2J generates .4 to .5 more "G" force with the fans turned on than with them turned off. Hall: "At first, the 2J was a real shocker! Side forces (in cornering) are really impressive. Holding your head upright becomes extremely difficult. On a normal Can-Am car you have to bend your head over about half-way to balance the cornering force. In the 2J the cornering forces want to bend your head right over. We're going to have to get used to it. I've banged my elbows and knees on things I never used to touch. Another change in the 2J performance over past models is the quickness and directness in steering. You get a direct change in direction when you turn the wheel. The downforce increases the contact load betwween the tires and the road without increasing the mass (weight) of the car. Steering effort is high and any little change causes a significant side force."

All of this added downforce wasn't without some weight penelty. That added weight comes from the extra engine, the vane-axial fans, necessary skirts and ductwork. Another problem is that the high G loads on the car put added stress on other components. The 2J has been designed and tested to safely withstand 2G load in any vector and/or any combination. Cornering, for example, combines G loads in at least two or three directions. As much as 55 percent of lap time in a Can-Am race is spent cornering and braking. You begin to see the magnitude of Hall's concept.

The suction has minimized another probelm on every Can-Am car: too much power. Wheelspin can be induced at any speed up to 150 mph on normal Can-Am cars. With the 2J, the suction virtually eliminates all wheelspin, even from a standing start. Drag fans, take note.

What about top speed? This static downforce system adds little drag on the car while producing tremendous downforce in aerodynamics over wings and spoilers. And since aerodymanics are important to top speed, not using them keeps drag at a minimum.

Various combination of fans, drives and auxiliary engines were experimented with, but the final system uses two vane-axial fans driven by a two-cylinder, two-cycle JLO (pronounced "ee-lo") auxiliary engine. This method was preferred over driving the fans from the main engine because the auxilary engine keeps the fan speed constant. If the fans were driven from the main engine, fan speed would vary as the main engine speed varied; so would the amount of downforce.

Naturally the question will be asked about failures in the fan system. Failure of one fan during the race results in less than half the downforce loast because the other fan would speed up to partially compensate for the disabled unit. In the event of both fans failing, of couse, the cornering would suffer.

Fan placement was experimented with, but the final location was at the rear. Easy maintenance is a necessity. The entire engine and fan package can be replaced in minutes. Simulated failures have been programmed into the car testing. The vacuum reservior loses its effect gradually, and allows the driver time to take appropriate action. Tom Dutton, 28, will help test drive the new 2J. Tom's career began, appropriately, in a B Production Corvette in 1966. His most valuable asset to the Chaparral program is his ability to drive and diagnose a problem and fix it himself.

To make maximum use of all this downforce, the widest tires made mount to the 2J. Three and one-half feet of tire width will grace the rear of the new 2J car. The car brakes better than any previous Chaparral, too. "I simply can't believe the braking capability of this car." says Jim Hall. "It feels like it will decelerate about twice as fast as any Groulp 7 car I've driven."

The 2J has set a track record at Chaparral's Midland track, where Hall tests each of their engineering tours de force. And Hall casually remarked that he was not driving the car at its full potential that day.

the computer played a role in skirt design, too. In fact, a rivalry sprang up between the live, flesh-and-blood engineers and the inanimate computer. The design resulted in about two parts live engineer, one part computer. Horray for people! The goal in skirt design was to run about 600 miles without maintenance. The closer the skirt hugs the road, the better the suction. The Lexan material proved more durable.

When you see the Chaparral 2J, at Can-Am races, look it over carefully. You won't see and rear wheels. When it starts, there'll be a different sound. first, the sound of the booming ZL-1 engine. Then the raucousness of the auxiliary engine and fans — earsplitting. And when all of this happens, you'll see the 2J hunker down as the suction takes hold. Out on the couse, well you wait and see.

There's never been a Can-Am car like the Chaparral 2J. The incredible Chaparral 2J.