Dual scroll part in this terminology means "twin-vein" in essence. There are two routes for the exhaust gas to enter the Turbocharger split between the 4 piston banks. So gas from two of the firing pistons enters one route then the next two pistons fire and their gas enters the other route. It permits a continuous flow of exhaust gases that do not interfere with each other on their passage to the Turbocharger.jarcher said:What does this mean? Does this mean that there are two wheels, a big one and a small one, for different rpm ranges?