Building a fast car is always a matter of money but first first let us burst a myth
More money = Fast car
Not true. Spend your money wisely and not foolishly. More money can get you an expensive car but not necessarily a fast car.
What is a fast car then?
A fast car does not mean only in terms of top speed but fast in terms of going through a particular challenge or track fastest. So before you start a build you need to determine what is the challenge or objective that the cars is being built for.
For example if the competition is a quarter mile drag then your build should focus on acceleration. From engine. From gear box. From aerodynamics. From tyres. From turbo. From nitro. From weight reduction.
A high revving engine does not last long. Do not expect the engine to be built only onec.