At high speed, your engine will be working very fast and the valves opening time will be very short that's why Lift technology came up which let the valves opens more so more air can enter the CC for combustion and more power. On ordinary engine with no Lift on NA much will suffer at higher RPM....choking because the engine can't get enough air inside to CC to create more power. That's why you see those hp torque chart always start to drop like flies after a certain RPM. More air into CC more power you have that's why intake and exhaust mods have so much affect on an NA engine.....on FI, the turbo helps cramp the air into the CC....
TO achieve speeds in range of 300 or over....aerodynamic, gearing,suspension and power play very important roll....higher the speed your car will generate more down force and more pressure on the tires....power is to help you get there, aerodynamic is to make sure your car don't flip over or float at such speed, suspension to make sure you still have control, gearing gives your more speed..
On the weight side, a lighter car with more power that can achieve 300km/h or more will be heavily relying on aerodynamics improvements to keep it planted on the road. That's why you see race car have so much aeordynamics parts on them and when 1 of the parts get damage you can see their lap times get slower...heavier car they already have weights in the 1st place so aerodynamics add on can be lessen but it's still as important.
Renesis VIII, This is an Evo I used to drive in Japan....450hp...capable of 280-290km/h I've done some on the aero parts...It has flat under panels too...the pic is before put in the rear diffuser..
