As electronic fuel-injection continues its growth in drag racing, a few more tricks are coming across from other areas of motorsport into the sometimes stubbornly traditional drag racing world – Just take a look over at Pro Stock. One of those tricks that EFI makes relatively easy to implement is traction control, as the ECU can accurately control engine output.
Traction control looks at a few inputs to detect when there is wheel spin, and then decides when it should reduce engine output. Unlike the OEM traction control in your modern family sedan, which uses aggressive spark or fuel-injector cuts to control engine output and is effective at slowing a driver down as quickly as possible, aftermarket ECUs like the MegaSquirt 3 Pro (MS3 Pro) can smoothly reduce power as to control wheel spin with minimal speed lost.
It does this by looking at both wheel speed and engine rpm to determine if there’s wheel spin. With wheel speed (using two vehicle speed sensors) the MS3 compares the wheel speed of the front and rear wheels, and waits for the rear tires to spin faster than the fronts. The driver can dial in how much slip is allowed before the traction control steps in, giving him flexibility for different tires and surfaces.
You can see this front vs. rear wheel speed data in the lower left of the video above, where the bar on the left is rear-wheel mph, the bar in the center is the front-wheel mph, and the bar on the right shows traction control intervention with the total degrees of timing retard being used.
Of course, there are those of you who will ask: “But, my car does a wheelie to eighth-mile; how will it look at wheel spin there?” In this case, where the front wheel speed would read significantly lower than the rear tires as they hovered across the pavement, the MS3 Pro can be set up to look at the “slew rate” of the engine rpm to determine if the engine is accelerating quicker than possible if it was hooked up – EX: when suffering from wheelspin.
In drag racing, assuming the car is driven consistently every time, we can predict a myriad of driving events accurately, which is why we have timer-based controls for nitrous, and other power-adders. Engine rpm can be predicated to accelerate at a specific slew rate – basically a measurement of how much rpm the engine gains over time – and when the engine rpm exceeds a known rate of acceleration, the MS3 Pro can safely assume that the rear tires are spinning. Once the front wheels settle on the ground and register an accurate speed, the MS3 Pro will automatically switch to the wheel speed sensors for the rest of the run.
Once it does detect enough slip, unlike the hard-cuts used by OEMs – which would quickly shock-load and destroy parts in high-horsepower applications – it uses a list of methods to reduce engine torque smoothly, such as reducing boost with the wastegates, heavily retarding timing with coil-pack ignition, or controlling nitrous stages, to safely reduce engine torque and control wheel spin. The best part is these methods can reduce output while keeping turbos spooled up, keeping the engine safely fueled (by using anything but fuel-cuts to control engine output), and reacting quicker than most any driver could.
This is far more accurate than purely relying on timer-based, or per-gear boost and nitrous controls, as it is always adjusting output based on available traction, instead of a pre-programmed assumption of traction available.
Of course, it still takes a good driver to know when a run is lost, traction control will never replace common sense, but you will no doubt see it more often in due time – especially in more open events centered around no-prep racing.