they are the same as z1's 2.4 inch test and downpipes, i seen both side by side and there isnt any diff. as far as gregs his are larger diameter and better welds. i am running ebay dps and tps with no issues and i gained about the same power as the 2.5 in my opinion, i think they are the best bang for your buck, just inspect the welds for deffects, that is the only issue that i have heard about. I also have heard of fitment trouble but there were none on my set.