Heat soak actually applies ot pretty much any part of the engine bay that would normally perform better at a lower temperature. IE, the intake manifold, throttle body, intake tubing, compressor side of a turbo( though you pretty much can't stop this one) and especially fuel lines. A hot intake manifold and throttle body heat up the air that should have been cooled by the IC through convection, and thus rob some power. One thing you can do to help this (if you don't live in an overly cold area) is to remove the coolant lines that run through the throttle body, which obviously warm up the metal a rather large amount. The intake manifold would be much harder, as you would need to remove it, and shield the bottom with heat reflecting tape to help prevent radiated heat to the manifold itself. Fuel lines, if you want to go through the work, can be sleeved in insulating wraps, like the hightemp silicone coated fiberglass sleeves. Some people will say that all of these things will produce negligible gains, but if you do all of them, and help vent heat from under the hood, it is going to be more efficient, and help make more power. You can't of course fully prevent heat soak, but you can reduce it's effects on the components under the hood.