Welcome to GTPlanet, lumPwin. What are you trying to beat? The NSXs will beat just about all of the other JGTC cars, even in stock form. You may want to add N/A 1 tuning to it, but don't go overboard on power.
If the car seems to dog a lot when upshifting, move the "Autosetting" slider to the left, for closer gear spacing. After you do that, adjust the Final Drive ratio to the right, for higher top speed. Experiment a little and see how the car behaves when you make different adjustments.
