Well, speed is dependent on a few variables - there's your raw power, your gearing and your car's body (yes, drag coefficient seems to be simulated).
So you might want to try a ma-hoo-sive engine (Escudo, Speed 12 - although the Escudo suffers badly from lag), with huge power mods (Alto Works stage 3 turbo is the single most potent part in the game) and a Ford GT40 body.
For good cornering you'll need a light car chassis, coupled with F1 suspension (and a good set-up helps too).
As for AR codes, sodomy non sapiens.