Few, if any of the currently flying P-38's actually have an operational set of turbochargers mounted. Mostly they're quiet because they have most of the original exhaust system in place, usually with some tubing replacing the turbochargers, so that the exhaust exits in the same place, which is well above the head and ears of most people, pointing up and to the rear, directing the sound away from most people near the plane on the ground. Where as most piston engine fighters have what amounts to a set of open headers similar to those on a dragster or funny car you'd see at a drag strip (we call them "zoomies").
A set of General Electric B series turbochargers in excellent operating condition would probably be worth at least $100K. They add a layer of complexity to the aircraft that few would want to deal with.
I heard a real set on a P-38 decades ago. The P-38's you hear now sound great, with that deep throaty loping rumble that sounds like an over sized muscle car engine (think 67 427 L-88) on steroids. The turbochargers add to that sound, but they also smooth it slightly.
