coated pistons > polished pistons- better heat resistance and heat transfer is less into the piston and its a hotter burn. 4v> 2v- 4v have the plug placed in the center to start the burn from the center and work its way out causing a full, even combustion. 4v heads are meant to swirl they are meant to tumble, 2v heads need swirl to use up the space provided by the cylinder. intakes can be ported fairly smooth for carb cars, something around a 60-80 grit. Mostly due to better castings/ intake ports/ fuel