The PSP port actually has a difference in content with the console versions, including the choice for 3 setting types for the car instead of 2 (which could be attributed more than everything that it's a port by another developer), the initial set of unlocked cars for each class being 3 instead of 6, the track layouts being completely different, and the Time Attack in the PSP version being based in passing checkpoints under a time limit for the longest distance possible (similar to the Arcade games) instead of a standard solo race.
The Subaru Impreza WRX STi was, at the time, the latest in the successful line of Subaru Impreza impreza rally cars, some featured in Sega Rally 2. This was the first car to be implemented in the game and formed a basis for all the others.
Likewise the 1999 Peugeot 206 WRC was in the Game Boy Advance game. This too has been updated for Revo.
Citroën Xsara Rallycross
Peugeot 207 S2000
Citroën C2 Super 1600
Toyota Celica VVTi
Grande Punto Rally
Toyota Celica ST205
As is a tradition with Sega Rally games, the Toyota Celica CT-Four ST205 from the original Sega Rally Championship is selectable in Sega Rally Revo from the get go. The decals are slightly different due to licensing issues (and errors in the first game) but the car is largely the same.
Lancia Super Delta HF
Likewise the Lancia Delta HF Integrale from Sega Rally Championship also makes an appearance, albeit with minor cosmetic differences.
The Lancia Stratos, a secret car in the original Sega Rally and more predominant in Sega Rally 2 also makes an appearance. Its default appearance does not match that of the first two games, but this paint job is selectable.
Ford Escort RS Cosworth
The Ford Escort RS Cosworth makes a return from Sega Rally 2.
Audi Quattro A2
Peugeot 205 T16 Evolution 2
The Peugeot 205 T16 was first seen in Sega Rally 2, and returns in Revo.