This can be done in most of the top class cars, the McLaren F1 is the most forgiving for the power/speed with the TVR Speed 12 getting a bit hard under braking with the F50 taking no prisoners at all!
Everyone knows a race is won and lost in the corners on this game, i would recommend using the F50 and adopting a trailing input technique:
Braking into the corner:
Trail off the accelerator, but not 100% i know it sounds daft but you have to keep the balance of the car correct (this is where i find this game more realist than gran tourismo)
Brake into the bend with never more than 75% full braking power, feel it in, dont hammer it in!
Powering out of the corner:
The same as above but in reverse (i dont mean go backwards!) always keep that tiny bit of pressure on the brakes and only feed the power up to 75% sometimes i would pulse this amount anyway just to always be on the edge of the available traction. Then as you straighten up go WOT.
This is really from the point of view of the F50, although adopting this technique in class b and c races will have you running rumble-strip to rumble strip perfect.
If there are some still available have a watch of the hero's channel on LIVE you'll be able to see this working in the races.
(on TS rating 30+ winning a race will be the same as almost lapping the opposition in the single player career so get online and race :-} )