Originally Posted By: ZeeOSix
The louvered center tube is probably fine if the louvers cover the whole (or close to it) center tube area. If someone cuts one open, they could measure the area of a louver and multiply that by the total number to see how the total flow area comes out. I'm thinking it will be adequate.
Like a lot of things, if someone has an experience it sticks. I bought a filter with the slits at WM a few years ago, or more, and the slits were not opened, most of them, or only a tiny amount. It was a super tech I guess, returned it. Now many are using the slits. The TRD and RP have slits, Baldwin, now Purotator. I like the punched out round holes and forget about the spiral it only makes a ridge to mess up the holes.