So i am looking to make a cat for my b18c type r swap in my 2000 si since the collector flange is to small. The cat that's in it now is 17 inches long and i've found a universal Magnaflow cat that's 15 inches and i figure once I get someone to weld the two flanges on it will be about or almost 17 inches again. I already ordered a 2.5 inch collector flange to cut off the old cat and weld on for the mean time. When i get a couple extra hundred dollars i figured that i would buy everything since the stock on is kinda beat up. Just a project and wanted some advice if anyone else has done this and what brand's they used thx.

 

I did this exact same swap a few years ago, I used the 2.5 Blox flange its the best fitting aftermarket collector flange. If you need a donut gasket get one from an s2000. The magnaflow cat i used is part# 53006. You will also need a 2.5" three bolt flange if you want to bolt up your stock or aftermarket exhaust. I have a few extra 2.5" three bolt flanges, let me know if you need one I'll give it to you for cheap. You'll also need a piece of 2.5 pipe to extend the cat a little.

 

I actually just got my hands on a Jdm Itr Cat so i am just waiting for it to come in the mail. But thanks for the offer and reply.

 

That's the best option. I did it myself, saves a lot of messing around when going oem, and in a lot of cases would be cheaper too! Paid $75 for mine