Regular 5.0&SF readers know we're all about numbers. And when it comes to performance projects, we usually have dyno numbers to back up what we do. They're a great way to find out if you're making headway with performance gains or if you're taking a step backward. But, as the saying goes, "You don't race dynos."
This is never more true than when you build a car for competitive drag racing. While it may make 650 hp on the dyno, what it puts to the tires to ultimately get you down the track is an entirely different scenario. Horsepower at the rear tires is affected by many variables, including parasitic loss of the drivetrain (trans, rearend), the fuel system, cooling ability, differences in parts between the dyno and the car (headers, for example), and traction, among other factors.
Ask just about any racer and he or she will tell you that after engine break-in and fine-tuning on the dyno, the real challenge is track testing. There, weather, chassis setup, and other variables need to be tested and retested to make the most horsepower and to put that horsepower to the ground every time. Realizing your supercharged Mustang won't make the same power from a 60-degree day to a 90-degree day with high humidity is the first step in track testing. Ever notice how your street Mustang feels a bit "crisper" and has more acceleration on a cool morning? That's the denser air charge and cool temperatures affecting the engine's ability to make horsepower. Adjusting your car to make the optimum power for the driving conditions (weather, track, tires, and so on) is how you'll lay down the best times.
To give you a racer's eye view of track testing, we followed along with NMRA racer Uncle Robin Lawrence to see what's involved in becoming a competitive racer. Seeing as how Robin spent the last year in Real Street, having moved up from Factory Stock, he has had to spend a lot of time with a new engine combination, a new chassis setup, and different tires. This all means lots of track testing for him to get a good idea of what his combination is going to do at a given track, elevation, and weather condition.
Tools Of The TradeBefore you head to the track for testing, make sure you have the right measuring equipment. Bare minimum is a weather station (or the proper gauges to read temperature, humidity, and barometric pressure), a tire-pressure gauge, a logbook to keep track of changes and progress, and a formula or racing program to equalize the results from one day to the next (referring to weather conditions). A laptop is always a good option as well.
Robin uses a Computech weather station kit that includes a preprogrammed calculator. The calculator helps equalize his testing from those 60-degree days to the 90-degree days. It also has a built-in e.t.-prediction function that will accurately predict the e.t. after inputting the current weather conditions. Robin uses his Auto Meter datalogger to look at various channels of data (more on that later in the story). The Data Facts software is yet another reason he has a laptop in the trailer during testing and events.
We mentioned in the lead caption that Robin keeps an Excel spreadsheet of his runs on his laptop. He records not only the initial data found on the track's timeslip, but also the incremental times between each segment of the race. As you can see by the example shown here from Robin's testing, he can ignore any variables caused by starting-line traction and concentrate on the incremental times, which will show you the true horsepower he's putting to the ground.
While everyone's car will differ somewhat in the functions that will be recorded or watched, the basics for a supercharged Mustang can be covered with the following functions that Robin watches on his datalogger.
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