Youtube it. Seriously, racing games almost never can be explained (especially for lap times) with just words.
As for general advice (I haven't played the game,) try using cars with different accelerations and top speed combinations. If the track is full of sharp curves, stick with acceleration so that your top speed climbs up to high speed while it is better to have a higher top speed than plenty of acceleration if the curves are few and you find that your speed caps out too quickly. If possible, could also do some combination of high top speed and using boost to cover acceleration.