A bit like coaching, do a 2 day course and read a few books, find an athlete already performing and hey presto, tinkering. 
All jokes aside a mates son used to import rear cuts and use the parts to build Evo’s well before they were imported into Australia. When the Evo’s started to be imported he stopped and I was given a part built motor to go in my 1989 Pulsar used for hillclimbs. I did all the work on the Pulsar myself, the ex-standard motor is non turboed and goes a bit stronger than the best factory one ever did, it fries tyres in 3 gears. Only problem is finding the time to drive it now days and yes it is past the stage of being able to be road registered.
I find it interesting that Asapha has works on his own car, shows he is a kid at heart. Any mug can acquire something already done.