Unlock Honda S2000:
     Finish  quest  mode and Honda S2000 will be available to buy when
you start a new game.

Unlock Porsche 911:
     Finish  quest mode twice and Porsche 911 will be available to buy
when you start a new game.

Never Lose Kudos:
     When  you about to lose in a race, press A, B, X, Y, and Start at
the same time so that you will go to the title screen. Go back to your
last  save  and you will have the same kudos as before. Don't try this
during the second stage in a championship race.

Earn 1000+ kudos:
     In  every chapter, you will be given 2 hotlap races. They are the
easiest  ones and they dont have time limitation. You will be required
to  beat a lap time in one of those 5 laps per race. First you set the
lap  time  required to max (it is default) then in the first or second
lap you have to beat the time (its so easy). Now you have 4 more laps.
Now you can do as much tricks as you want, no time limitation. You can
spend  5  or six minutes per lap executing tricks, I mean powerslides.
Just  speed  up and turn left or right with the handbraking a "k" will
appear  on  the  screeen. (That means that you have made a trick). You
can go backwards to have more place to do tricks. Execute the trick as
much  as  you  want  and when you finish the race you wont believe the
kudos you have earned. I achived the required time in the 1st lap then
then tricked for about 8 minutes and I earned 3000 kudos plus a joker.
By using the joker again (joker doubles the kudos) made 6000.