nfs carbon help

[cwilson]

i need help with a problem on the game. some of the cars dont seem to work correctly. the problem is when you buy them they work fine but when you modify them they seem to lose all power. i useually drive in manual mode and they wont rev up when on the move and i cant get past 3rd gear because of it and when i use the nos to try and help it just goes slower. how ever it doesnt seem effect the rwd and 4wd cars. has anyone got any ideas as to what the problem may be?