Thanks all. I tried all those cars (except the Concept Car because I couldn't get it ) but the car I found really helps, is s Honda S2000 with a few mods. You can mod it right up onto the HP limit, or around that area.
You won't lap them unless your good at the race, but you can win by about half a lap.
The factor that held me back in the endurance races were my tires. They were too soft, so I had to pit like every 5 laps. I went to hard tires, and only had to pit every 10 laps, now when I lap the AI cars they stay lapped.
I've used the Prelude tuned up to 288 Hp and won by 2-3 laps. I ran it today in the Mazda RX7 GT-C, completely modded out EXCEPT for HP modification and won by two laps. The closest thing to me was the Fiat Barchetta.
I have never seen the Vector in this race. Maybe my version of the game has that ugly little bug worked out.
Oh yeah, I forgot. On the Mazda I used the Super Soft tires and only had to pit in one time.
On GT 3 I would have had to use Racing Slicks or I would have had to pit in every 2-3 laps.