I was looking at the B pipe flange after I remove the cat and Comptech header to install my new JDM ITR 4-1 header and noticed the hole looked kinda small so I measured it and it measured 1-7/8", not 2.25" like the rst of the exhaust. I then proceded to remove the B pipe and I used my dreamel (SP?) to enlarge the diameter and match the B pipe diameter. The whole process took my a lil over 1 hr, not bad. I am going from a 2.5" header and cat to a 2.25" exhaust all the way to the muffler, instead of 2.5" to 1.875" to 2.25". I checked the rest of my exhaust flanges to make sure there was not another restriction and I could not find one, so i think I truly have a 2.25" exhaust now. I called Comptech to ask them why they built the exhaust that way and they said that the exhaust was menat to be used with the stock cat which is also 1-7/8". I'll buy that!. I think I might buy an adapter from SMSP soon, but that will involve cutting part for the B pipe and welding the adapter.
Has anyone else done something like this?
I have learned a lot and if I was to do it all over again, I would do a lot of things differently like NOT buying just because it is BRAND name that EVERYONE uses, but I would have my exhaust custom built or buy a SMSP exhaust for example.

 

what else beside the smsp exhaust is 2.25" or larger?

 

Thermal, Greddy, Tanabe but I think they might have restricitions also. I know for sure the Tanabe racing medallion has a restriciton also at the B pipe right after the cat.

 

so does this mean that every exhaust made to fit my stock cat is gonna have a 1 7/8 diameter in it? If so i'm gettin a car sound cat and thermal stealth custom done by SMSP

 

uuuuuuh

could you tell a difference? hummmm
makes me wonder.

if this is true, which i totally believe, then every one of us with a cat back exhaust has the same bottleneck, assuming we have a cat, right? would a random tech cat be a bottlekneck too then?

 

dude, it was very easy to modify the B pipe with the right tools! I don't know for sure, but what you said might hold true. PROBABLY, every aftermarket catback is designed to match the STOCK cat, so if anyone is replacing their stock cat for a bigger diamter cat like Carsound, don't forget to look at your B pipe flange as well.