Endurance races in Gran Turismo 3 are a bitch! The easiest one, im my opinion, is the Roadster race. All of the cars are stock roadsters, so it's fairly easy to get a useable car from the start. I used a Mazda LS with super-slick (AKA high-endurance) tires. It took over 70 minutes to complete 40 laps, but I demolished the competition! I lapped everyone and almost double lapped the slowest car. There are four possible cars you can receive after winning this race (F688/S F1, Mazda Miata, Mazda Miata 1.8 RS or Mazda Miata RS) and of course I got the worst one (the plain Miata). Sigh.