i'm running a 3.5 pulley with colder NGKs, FWI, and a 180* tstat. i'm looking through ZZP for a downpipe, but i'm given a ton of sizes and special trims. off-road, shorty, with a cat, etc.

i don't really want to go with welding, but i really don't know what the differences are between these. i hear you should go with a 3", so that's where i'm trying to troubleshoot.

any ideas on which would be the most efficent? i appreciate the input!