My best chase scene was for a WWII Modern Game I had going. The PCs were allied spies working in Prague. Due to a series of mistakes, they thought their description was out (it wasn't). They were just coming back from infiltrating an abandoned research facility (Himmler meets Umbrella Corp.

), our heros are stopped at a checkpoint. The charismatic hero failed a series of esy bluff checks (rolled a 1 and a 2 on a row) so they were asked at gunpoint to get of their car. The psychotic wheelman (+15 Drive) decides it's time to run for it and the even more psychotic sniper takes out the SS liuetenant at the checkpoint.
What followed was a desperate car chase through the industrial sector of Prague as the Nazi tried to stop this heavy truck while chasing it with motorcycles with sidecars. A lot of, shooting, grenade throwing was involved. The wheelman player was great help at this point cause he really got into it and would come up with great maneuvers. About all that was lacking (to my shame

) was that i didn't include a fruitcart. Everybody knows you can't have a chase scene without a fruitcart. Or water barrels.
IIRC, the chase was into a stalemate because the Nazis had enough time to blockade all the streets, until the wheelman decided to use the rail embankment to jump over a canal. Through an incredible roll, the use of an action point and "GM coolpoints" due to the awesome idea, they were able to make the jump. A the psychotic sniper had already jumped on a moving motorcycle and taken control of it. He didn't quite make the jump (he did survive the massive damage from the explosion though

)
What I learned from this scene was:
1) have to add random obstacles (I ended up adding it on the fly). Your rules will help out greatly here.
2) using the Modern vehicle rules is slow. Specially if you have to be drawing a map of the area and everybody get's a move and an attack action. Chases should be fast-paced and PCs should react quickly to a changing environment. With the rules set up just as in combat, the players went into deep tactics mode which slowed the chase down. I think cutting down to one action per player will really help, as well as running the chase with a good action soundtrack in the background.
3) for a good chase in which the heroes are the prey yet they're tougher, you just gotta keep adding bad guys into the mix. With enough bad guys, yous start seing desperation tactics from your players which greatly add to the enjoyment of the game.