In Texas we know a little something about heat, 110 just isn't fun unless you've got at least 90% humidity thrown in as well. The best advice I could give is keep yourself in good physical condition. Hit the gym at least 4-5 times a week, eat well, no alcohol for at least 24 hours before an event, get a full night's sleep, no caffine, carbonated beverages, cigars or sugar in your system by grid time (or as little as possible, sugar is the enemy of judgement, ever read the label on where those carbs in sports drinks come from?). Want to pick a sucker? Find the guy up late in the bar with a stogie and a few drinks in him the night before an event and bet pink slips. You'll need a trailer for his car before you leave the track Sunday.
Heat is your friend if you are used to it. Train into it and when it fatigues the others you clean up. Not that a cool suit isn't a great idea, there's a reason they are so popular. My favorite is a cool down shower between heats, and sticking your hands in an ice water bath to radiate heat. Just like skiing or skin diving the hands and head radiate a lot of energy. An ice water towel on the face is very refreshing. And never forget to keep your mental attitude in the best of shape. Check resentments and distractions at the gate, the body follows the mind and attitude is everything. Greeting your fellow drivers with a cheery "Good morning! Who's coming in second?..." always sets the proper tone
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Make sure your car is ready too. Differential coolers, upgraded power steering coolers set in the fascia intake, vented hoods are all insurance that you won't have to trailer home what you drove to the track. If you've added horsepower under the hood there's a good chance you've added heat as well. Change fluids after every event, or during if it's a long hard weekend. That goes for the car too.