Let's take a perfectly good, classic sports car like a 1987 Lotus Excel SE.
One of the immediate challenges is to be able to close the bonnet.
That meant cutting and repositioning the radiator reservoir, and making up pipes for
the fresh air intake - where could air be cleaner than in front of the radiator, underneath the scoop?
The air intake pipe is 2", which is a lot less than the 3" feeding into the plenum,
but it's the maximum width pipe that will fit next to the radiator.
The dropoff in power is minimal.