1. When you collect enough credits buy a Dodge Challenger. It's cheap and powerful. You can upgrade it to well over 400 horsepower!! It's a bargain! A new transmission, Super Soft Racing Slicks, and a limited slip differential are recommended. I used a racing transmission and a racing differential. These parts won't be cheap (the tires are about 17,000 but at least the differential is 7,000). But they are worth it. The car can get oversteer easily as you add power. So use caution.
2. Buy a Dodge Viper when you can. It is a powerful car that will win you many races. The best modifications to do are Super Soft Racing Slicks, a racing transmissions, sports brakes, brake balance controler, 1.5 limited slip differential, and weight reduction. The handling of the car is surprisingly good even when you decrease weight and add power.
Bonus Cars
FR Challenge: 1st Race- Nissan Sileighty 2nd Race- Nismo 270 R 3rd Race- Toyota TRD 3000GT? or RX-7 GT-C?
FF Challenge: 1st Race- Honda Mugen Accord Sir-T 2nd Race- Tom's T 111 3rd Race- Mugen Prelude Type S
Luxury Sedan Cup: 1st Race- Honda Accord Type-R 2nd Race- Toyota Chaser TRD Sports X30 3rd Race- Nissan GTR Autech Version Tuned by Nismo