There are a few ways to go about this. You could either modify an existing Crown Victoria or Town Car, or you could build one from scratch. If you're modifying an existing car, you'll need to make sure that the engine is capable of producing 400+ horsepower. You'll also need to upgrade the suspension and brakes to handle the increased power. If you're building a car from scratch, you'll have more freedom to choose the exact components that you want. Either way, this is not a project for the faint of heart. You'll need to be prepared to put in a lot of work (and money) to get the results you're looking for.