i have a carsounds now, but if i decide to get a comptech or JG header, can i still use my factory cat or will it lose its effectiveness for not being used for so long...

 

You can still use it. I didnt use my cat for about 2 months while i was using the JDM DC header with the carsound cat. When i went back to stock i used it for another 2 months, then took it off and reused the Carsound, with the JG header by IB. Also If you plan on using the Carsound w/ the JG, its going to be too short, you need to extend the b-pipe by about 2 inches

 

well, i would imagine it would be fine, but if i were to get a different header, i would keep the carsound cat...much better flow...why put the stock one back on?

 

i want to use the stock cat cuz the carssounds is a 2.5 OD, and the comptech and JG are not. though i have heard that the jg comes in 2.5 od...

 

This is correct the JG is a 2inch, what import builders does is they cut off the collector and weld on a 2.5 inch one. thats whats so modded about it