In the late 70s we ran a 413 stocker with 2 inch adjustable hookers and 3.5 collectors.One weekend we substituted 3 inch Stahl collectors just because we had them and were curious. The results were stunning. Can't remember exactly how much better but we never went back. Of course the craftsmanship was much better in the Stahl collectors. The collectors on my current motor are junk compared to those old Stahl pieces so I will only suggest you look for guality as well as size in today's parts market