Aero is one aspect. There's complexity to going over 300 mph without doing a Mark Webber.
"Most speculators have settled on around 1,800bhp being the predicted amount of power needed to push a car to 300mph, but power isn’t as big a problem as you would think – the real issue is cooling things down and the consequences of doing that.
The established method for cooling down the excessive heat an engine produces is by channelling the vast quantity of air that rushes past the vehicle as it moves over the hot parts to strip away the excess heat. It's a simple and elegant solution; the faster you travel the more you need to cool, and the faster you go the more air you are provided with. It’s perfect - except for the drag that’s produced.
As you channel that air through intakes and scoops, those gaps and holes reduce the aerodynamic efficiency of the car and cause drag. And the faster you are travelling, the more that drag slows you down and wastes more of the power produced by the engine.
Of that 1,800hp estimate, almost 1,500hp of it will be used just to overcome the drag of the vehicle.
You’re now faced with solving one of the conundrums that has so far prevented engineers from building a car that can reach 300mph. How do you add more power to an engine which then needs to be further cooled, but cooling then slows down the car by increasing its drag".