I think 1-3/4 is for more ''stock'' type applications and 1-7/8 is for applications for a supercharger ect ect dont quote me on that though im not entirely shure
The 1-7/8" headers work very well for the Raptor 6.2, stock or modified. Stainless Works currently uses an 1-3/4" for 5.4 Raptors and it makes great power as well. Due to the displacement of the motor and the fact it already makes pretty good power from the factory the 1-7/8" design allows the motor to breathe better across the RPM range. Add an intake and tune and its a whole new truck. Increase tire size and get stuck in a mud hole, your will want the additional power!
We offer a number of options for the Raptor, including headers to factory catback or for the ultimate exhaust setup check out our True Dual setup which utilizes a high flow X-Pipe and dual mufflers! Sound and performance all in one package.