On Gran Turismo, why can the 3000GT get more power than the Lister Storm?

This is a trend that continues from Gran Turismo 2 all the way to Gran Turismo 4. I Understand that Gran Turismo 2 was picky about giving HP to cars like the Storm (It can't even get an NA tune up), but In 3 and 4 the treatment of the Storm Race Car is ridiculous. In both games, the can't even gain more than 900 HP, and in the latter it is capable of getting a high performance turbo kit. Meanwhile, the 3000GT, one of the pet cars of the series, can get over 1000 HP in GT3 and over 900 HP in GT4, presumably using the same turbo kit given to the Lister Storm. Are the makers of this game honestly suggesting that a small block Mitsubishi V6 is a more potent engine than a 7 liter Jaguar racing V12? Why is the horsepower potential of this car so limited, I figure that it should be making well over 1000 HP?