Actually I would think that it would take longer to heat up your tires so grip in reality would be less. But the car is faster. It's been many years since I've seen anyone do it for online racing. In reality the default coding of NR2003 has HP limits for each track/chassis type. I doubt that you are going to increase it no matter what you try.
By Ziggy
Test track - Talladega, clear skies, 70 degrees F and no wind. Top speeds in MPH, drag number rounded to nearest second.
Chassis 0 - Mystery car - Huge torque, huge drag, likes the psi 42 all the way around at all tracks, tires never wear out unless you have pits set to 4x and slam the brakes and hold them there. Then you will get them to wear. Idles at 800 RPMs while the other chassis idle at 1000. Get really bad fuel mileage. Has the same HP for all chassis.
Cup - 745 HP, top speed 189, 5 drag
GNS - 745 HP, top speed 187, 5 drag
CTS - 745 HP, top speed180, 7 drag
PTA - 745 HP, top speed 192, 5 drag
Chassis 1 - Restricted Aero - low drag but fixed spoiler, fixed rear shocks, fixed rear springs, left side track bar can not be higher than the right side. Likes the psi at 28/48 at ovals, 48 all around at road courses - stable at high speeds, low grip at low speeds.
Cup - 370 HP, top speed 189, 9 drag
GNS - 342 HP, top speed 181, 9 drag
CTS - 550 HP, top speed 181, 6 drag
PTA - 625 HP, top speed 212, 7 drag
Chassis 2 - Banked track - Medium drag, downforce on the nose, rear feels a bit light, likes the psi at 28/48 at ovals, 48/48 at road courses, stable but a bit 'twitchy', sensitive to steering input -
Cup - 635 HP, top speed 208, 7 drag
GNS - 623 HP, top speed 206, 8 drag
CTS - 562 HP, top speed 186, 6 drag
PTA - 625 HP, top speed 210, 6 drag
Chassis 3 - Flat track - Medium drag, even downforce, maybe more side force, likes the psi at 22/34 at ovals, 34/34 at road courses, stable, easy to recover -
Cup - 637 HP, top speed 203, 7 drag
GNS - 622 HP, top speed 202, 7 drag
CTS - 562 HP, top speed 185, 6 drag
PTA - 625 HP, top speed 207, 6 drag
Chassis 4 - Road course - Medium drag, even downforce, maybe more side force, likes the psi at 22/34 at ovals, 22/22 at road courses, stable, easy to recover -
Cup - 640 HP, top speed 204, 7 drag
GNS - 622 HP, top speed 203, 7 drag
CTS - 562 HP, top speed 185, 7 drag
PTA - 625 HP, top speed 207, 8 drag
Chassis 5 - Unrestricted Aero - Low drag, stable at high speeds, low grip at low speeds, likes the psi at 28/48 at ovals, 48/48 at road courses, left side track bar can not be higher than the right -
Cup - 706 HP, top speed 232, 11drag
GNS - 622 HP, top speed 226, 11rag
CTS - 574 HP, top speed 190, 7 drag
PTA - 625 HP, top speed 212, 6 drag
PTA car appears to be least effected by the chassis # although I have to admit I have the least experience in it and it took many attempts to get any data because I'd wreck or nearly wreck every lap. Just not at all used to it. :-(
Chassis # affects when the tires go yellow and red as well. Chassis 4 tires go yellow at 220 and red at 240. I think chassis 1/5 have to be at 240 to go yellowand 270 to go red I can't recall and haven't recorded those numbers yet.