I made a video guide for this and uploaded to my youtube account.
You can do faster on "Jason". His car is crap but the RPM comes faster then Lucas.
1. Go to RIMS then INTERIOR and pimpt both with max stars, rims with 4 and interior with 5.
2. Go to BODYKIT and right before you should get a Xzibit challange.
3. Go to CHALLANGE and head back to BODYKIT
4. On the way you should get the RPM CAR
5. Drive left and make a break, the car should drive right of you
6. Slam him until he is down, and use your nitro to make more damage
7. Press pause and exit the pimp-phase to save
8. Repeat