Never done any modding before but I've been reading and watching extensively about. While I've got a good collection of newer cars from the last few years I've also got a fairly good collection of cars from my childhood that I used to compete with friends with. Some of these cars have great "genes". They are built super solid yet not too heavy. I like these more than current cars.
My old cars fall into two categories. I've got some that back in the day were monsters but have since degraded over time. However nothing has changed with their build. Ive got others that can basically run with or beat all but a handful of new cars. We're talking brilliant performance.
What approach should I take for each type of car to get them performing their best? Looking at performance and not really appearance.