Data Logging Part 2: How to Use Data

In part one of this series, “Wanna Go Faster? Start Data Logging", we talked about what data logging is and showed you how to install a Diablosport hand-held tuner/data logger and a new Sportsman racing solution standalone data logger from AEM Performance Electronics, their AQ-1 unit. But once you’ve installed a logger, how do you use it? Can data help you go faster? Can it help you be more consistent? Can it help detect and diagnose issues faster? The answers are, we’ll show you how, yes, yes, and yes.

This year, thanks to some issues on our Maulin’ Magnum race car, we had lots of opportunities to put our data loggers to good use. The AEM AQ-1 comes with specific templates for sportsman drag racers, which once you learn how to use them make the task of logging and analyzing data easy and fast. Our Diablosport Trinity unit, like their inTune product, can log just about any parameter that your factory engine computer reads via the OBD-II port. The AQ-1 is the perfect unit for drag race cars that use either aftermarket EFI systems or for carbureted engines. On our car, we found both very helpful.

We’re going to talk about what the Trinity and the AQ-1 can do and show you some examples. All of the logs in this article come from the MoparMax Maulin’ Magnum, driven by Senior Editor Alex Rogeo with Editor-Publisher Richard Kratz as crew chief.

We’ll delve into details in a moment, but for now let’s start with a really simple problem, traction off the starting line. How many times have you said, “I spun the tires?” But where, how and why did you spin them? Was it true spin occurring right at the launch or did you shake the tires (also known as wheel hop)? The answer is important because the cure for spin is the opposite of the cure for hop. Do you want to just guess and use the next round to find out if you’re right or do you want to know right now and cure it before the next round? Yeah, us too.

Tire spin occurs when at the moment power is applied to the wheels the tires are immediately overwhelmed and start to spin. There is never a moment of traction. To solve tire spin you need to increase traction on the line. You can do this by changing tire pressure (usually lower), changing shock settings to plant the tire harder at the hit (on our car we would dial one ‘click’ softer on our Strange Engineering shocks rebound/extension adjuster), or changing your suspension geometry if you have adjustable suspension such as a 4-link. (Soft bushings in the rear suspension can also be at fault, but that’s not something you can adjust at the track.)

Tire shake (or wheel hop), occurs when the tires initially have traction at launch but it’s actually too much traction. The tire tread stays stuck to the ground and the tires build up big wrinkles that deform the tread in front of the current contact patch. The car starts to launch, but after a quarter to a third of a tire rotation the deformed tread has less than ideal contact and the tires lose traction and start to spin and hop up and down. On bias ply slicks on big power cars this can very violent, on drag radials it may not be as violent but it still means your pass is done right at the start. To solve tire shake, you need to decrease traction on the line. Again you use tire pressure, less shock extension, change the geometry only this time in the opposite direction of curing spin.

A data log can let you see whether you had spin or shake.

This is a normal, good acceleration curve as plotted on our AEM software. The vertical blue line marks the point in the time line that the car launched. The white line is the engine RPM showing the normal stall converter flash to the hydraulic coupling point marked by the white arrow. The red line shows a perfect, “Dead Hook,” drag radial tire acceleration curve. NOTE: The two spikes in the red driveshaft speed trace occurring at the 1-2 and 2-3 shift are normal, it’s just a momentary transient as the driveshaft unloads and loads again.