I used the Toyota Corolla AE86 and it's pretty fun. The upgrades are not realistic. For instance after getting every stage 1 upgrade and stage 2 upgrade for this car I'm pushing something like 230hp along with 698ft lbs of torque. What?
But what really pisses me off about it is they give you actual specs such as HP, TQ, weight, 0-60 and 0-100 times, etc. Or you can view them just as Acceleration, Top speed, Handling and Braking bars. These two types of specs which are like advanced and basic specs which you can toggle between one or the other, do not seem to correlate with one another. I toggled between them when doing upgrades to my car and noticed that when it would say that the upgrade wouldn't give me any more HP or TQ or faster acceleration times or weight reduction or anything, the acceleration, top speed, handling and braking bars would move. When the advanced specs would show increased acceleration in 0-0-60 and 0-100 and HP/TQ the basic bars wouldn't improve at all!
And I'm pretty sure it goes by the basic bars as to whether your car really does improve or not. Not the actual specs.
I also don't understand why they can't get the money system down right in video games. You earn money for races and sponsorships but the parts cost ridiculously too much money. Why couldn't they just give you less for winning races and be more realistic with the parts pricing? I can't remember anything specific off the top of my head but it was like $10,000 for a weight reduction or something. C'mon! Or like $25,000 for an upgraded turbo.
This game should be even more fun when I get this:
Logitech G25

Flatout and Flatout 2 are great games too. Really fun to play and I used the Subaru Brat in one of them to beat the whole damn game. Not that realistic of a game but very fun offroad racing game.
I plan on buying Dirt 2 as well. I have the first Dirt and it's pretty cool but didn't really keep me interested long enough to beat more than 2/3 of the game. I was pretty excited about Dirt 2 after watching a bunch of videos for it but then right before it launched they released some more videos showing stupid XGames stunts with fireworks or explosions and that stuff is dumb and I was hoping for more of a realistic rally sim. So I dunno how that game will turn out. Probably still decent.