The alloy steel rollcage that was almost complete in the last segment of Project S2K is now done and includes beautiful sheetmetal gusseting at the door bars, roof and rear X-brace, integrated mounts for the Spoon roof and a formed harness bar to give maximum seat travel. A well-designed rollcage like this one serves to substantially increase the bending and torsional rigidity of the chassis, allowing the vehicle’s handling balance to be tuned even with the use of stiff springs and antiroll bars. This is imperative to being able to get the most from the vehicle, and having a well-fitted and properly welded rollcage also provides the insurance of knowing—should something go horribly wrong on track—it will offer the driver the best possible protection. Now it’s time to continue with all of the welding and fabrication that needs to be completed before paint, which brings us to the air jacks.
Aside from the baller status of having your car lift itself up off the ground by simply attaching a compressed nitrogen line, there are several instances where an air jack system can be a real benefit. The most obvious is for race teams competing in endurance-type events where tire changes are required, and the use of air jacks effectively reduces the time for the stop. The next big advantage is you no longer need to place a floor jack under the lifting points to jack the car up. With our S2000’s target 2.25-inch ride height, side skirts and flat-bottom floor, getting even the lowest-profile floor jack in place would be inconvenient at best. Finally, you can use a special two-stage safety support stand that allows the car to be lifted to double the stroke of the air jack, providing ample room to work under the car.
There are some downsides, however, with added weight topping the list. You can expect to add approximately 15–20 lbs to the car by the time you include the jacks, lines, fittings, probe and mounting tubes. You will also need a bottle of compressed nitrogen (regulated between 100 and 500 psi, depending on the diameter of your air-jack piston and vehicle weight) to be able to raise the car. Finally, there is no really easy way to bolt the jacks in place, but with some careful planning, a hole saw and a welder, it’s usually possible to find a clean installation solution for the mounting tubes.
If you’re still considering installing a set of jacks, it’s time to pick your brand, size and quantity. If you’re racing a front-heavy FWD car, it’s often possible to get enough lifting capacity from a single rear jack so you only require three air jacks, making for a lighter and more cost-effective solution. Lifting capacity will be directly related to piston diameter and line pressure, so if you’re using a three-jack system it may be necessary to use a larger-diameter rear jack. Most manufacturers will state the lifting capacity for a given pressure, but if not, you can work it out with some simple math.
Since we know the total weight of a vehicle and its weight distribution, we know how much weight (and thus force) each jack has to generate and support. The force each jack generates is equal to the pneumatic pressure used in the nitrogen lines multiplied by the piston area of each jack. (To make our bottle last longer, we’ll keep the pressure regulated at 150 psi.) Basic geometry tells us that the piston area of each jack is pi times its radius squared. (Working in units of pounds and inches will be easiest.)
In the case of our Project S2000, with a 50/50 weight distribution and 2,200-pound total weight, we get 550 pounds per corner that each of the four jacks needs to lift. Just to be safe, we’ll say it's 600 pounds to compensate for the return spring and resistance between the tube and bushings.
Six hundred pounds divided by 150 psi means that each jack needs to have a piston area of 4 inches, or a piston diameter of 2.26 inches. Unfortunately, our JLS air jacks have a 1.75-inch piston diameter. Run the calculations again, and we’ll need 250 psi of line pressure to lift our target weight. The JLS jacks are rated by the manufacturer to a maximum of 35 bar (510 psi), so we’re well within the working limits and have more capacity available if needed.
With the jack sizing and quantity determined, it was now time to weld in the mounting tubes and install the jacks (see photos for how we secured our mounting tubes). We located the jacks in line with the factory lifting points to ensure stability when up in the air. This also kept the jacks within the wheelbase, helping to maintain a low moment of inertia (resistance to change in rotation). Our jacks did not include the mounting tubes, so we fabricated custom ones using 2.5-inch by .049 wall 1020 DOM steel. These were then MIG-welded to the chassis and rollcage where possible. The jacks are typically secured in the mounting tubes using large-diameter aluminum nuts just like on a coilover suspension, allowing for the placement and lift of the jack to be adjusted so all four corners lift equally. Next, it’s time to install the probe. It’s important to choose an easy location to access that won’t be damaged in an incident, and if possible, will not add any aerodynamic drag.
Since pit-stop time is not our main concern, we opted to place the probe behind the fuel door. Be sure to use a length of flex line to join to the probe because the line/probe will move together when releasing the nitrogen from the system.
Air Jack Shopping List 3 or 4 air jacks Air jack mounting tubes to attach to body (typically included with the air jacks) Air jack safety stands (mandatory when working under the car up on the jacks) Approximately 25 feet of line (we opted to use 0.375-inch aluminum hard line with –6 tube/nut fittings for a lightweight install, but braided flex line can also be used) Probe (attaches to body and is where the lance/nitrogen is attached to) Lance (attaches to nitrogen hose/regulator) Nitrogen bottle, 300-psi regulator and hose
Air jacks do take some time and fabrication work to install, and they will add to your car’s weight. So if you have easy access under your car with a traditional racing floor jack, then a set of traditional stands and a lightweight jack may be the best option. However, for low-ground-clearance cars with aero pieces or anyone needing to make fast tire changes, the quick serviceability and convenience that air jacks afford make them well worth the trade-offs.