July - August 1998 Lane Racing And Rodding Article By Jim Kaekel, Jr.
Many times, racers will make several changes on their race cars at the same time - jetting, suspension adjustments, and torque converter, for example - and find that their e.t. or lap time is significantly lower. Did all of these changes really help? Maybe only one change helped, while the other two actually hurt the car's performance. Or maybe another, entirely different set of circumstances was responsible for the car's improvement? One thing's certain - if that racer didn't take weather conditions into account, he'll never know the true answer to these questions. Tuning changes can never accurately be made to a race car unless weather conditions are taken into consideration. Changes to the jetting, timing, or suspension set-up on a car can be controlled, but the weather cannot. However, we can learn to deal with the weather, and tune that race car to perform consistently under varying weather conditions. This can be accomplished with the purchase a quality weather station, a computer designed expressly for helping the serious racer achieve consistency by adjusting for varying climatic conditions.
In recent years, we've seen the introduction of a number of sophisticated weather stations like those offered by Barry Grant. The Barry Grant Pro Model (#BGG130072) or Sportsman Model (#BGG130071) which feature digital temperature and humidity gauges, barometers, altimeters, and computers to process all the collected information. With these weather stations, the racer can accurately determine a dial-in using data from previous runs, factoring in weather information and data from runs at previous races. Information from one race to another can be compared and analyzed to tell the racer if the car is running at its peak...or if there might be a problem brewing.
At the track, in this case let's say it's a drag strip, the racer first makes a timed run. Immediately after the pass, the time and speed are entered into the computer, along with the temperature, humidity, barometric pressure, and altitude. The computer processes this information and yields a number referred to as Density Altitude. The e.t. can then be corrected to sea level (0 ft.).
Before the advent of weather stations for racers, a drag racer might have gone to the track, where the temperature was 85 degrees with 70% humidity, and run a 12.45 e.t., his best to date. Returning home, he might have re-jetted the carburetor and changed the torque converter, returning to the track the next weekend, where the temperature was now 72 degrees and the humidity was 85%. On its very first pass, the car runs a 12.40, a noticeable improvement. The big question is: did the changes cause the improvement, or was it the better weather conditions that allowed the car to run quicker than the previous weekend. Use of a weather station at this point could quite possibly show that the changes made to the car might have actually slowed it down. Theoretically, with the prevailing weather conditions and no changes to the car at all, it would have run 12.33, according to the data corrected for climate changes. The reason for this is simple - if you have a bachelor's degree in meteorology. Simply put, changing weather conditions affect race car performance. Even if racers don't necessarily have the time, energy and money to go to college to understand meteorology and how it affects the internal combustion engine, they should at least understand the basics.
There is one important fact related to racing and weather conditions, a fact which has a profound effect on all other weather data. The higher the oxygen content of the air that the engine "breathes" and the cooler the air temperature is, the more horsepower the engine will make, providing that it is properly jetted for the particular conditions. All other weather conditions relate to this fact. For example, that best run of 12.33 at a local track here in the midwest, where the altitude averages from 400-1300 ft. above sea level, may translate to a 12.26 at a track like Moroso Motorsports Park in Florida which is only 23 ft. above sea level. The lower altitude of the track in Florida yields a higher oxygen content in the air. This is why so many sportsman racers flock to the East or Gulf Coasts (Houston, Rockingham, Orlando, etc.) to set N.H.R.A. records, particularly in the spring and fall when cool temperatures create "mineshaft" conditions at these locations. A "mineshaft" condition exists when the Density Altitude is actually below sea level - considered to be a superior atmospheric condition as far as racing is concerned. When racing under these conditions, the racer must be prepared to richen up the carburetor(s). The higher the oxygen content of the air, the more fuel the engine will require to perform to its potential. It is the same principal whether it's drag cars, road race cars, or circle track cars. Elapsed times or lap times should decrease when racing under favorable weather conditions, as long as the track is ready for the additional horsepower being applied.
To understand the ultimate negative effects of altitude on a race car, let's take the same 12.40 car discussed earlier to Bandimere Speedway in Denver, Colorado, where the altitude is 5800 ft above sea level. Under temperature and humidity conditions similar to Florida, the car may only run a best of only 13.11, What happened to that low-12 second screamer? Without a healthy dose of oxygen in the air, its engine will not make the same amount of horsepower that it made in Florida, or even the Midwest. Professional Top Fuel and Funny Cars cars running at the Mile-High Nationals at Bandimere, compensate for the lack of oxygen by changing pulleys to increase blower speed, but naturally-aspirated cars don't have this luxury. High altitude means compensating for these conditions by leaning the jetting in the carburetor(s), "bumping up" the ignition timing slightly, and even installing lower ratio rear end gears in the car. We can't do anything about changing Mother Nature, but we CAN learn how to deal with whatever she throws our way. That's what weather stations are all about!