Was racing GT4 at my cousin's, and tuned up a nismo 270R (Silvia S14 I think) to 566 hp, put on Road Tires, got the car to break loose in 2nd gear, shifted into 5th, tires still spinning, and was only going 20 mph, while the cars top speed was 132 with the setup I was using.

Well despite the non-existant physics in GT4 what do you actually expect the car to do? Wouldn't the XRR do the same with masses of power on overbaked road tires (and 132mph is a short top for that powerful a car)?

yea, i know how bad GT4 is. I own it. The game doesn't seem right, my 3 le mans cars(Audi R8, BMW V12 LMR, Mercedes CLK-GTR race car) all top 1000 horsepower. Also i got the Ford GT to go 285 mph when tuned(798 horsepower with Nitrous that shouldn't be in the game).

Well, let's all look on the bright side of GT4, it's better than NFS:MW.