i got the dc sports jdm 4-1 with the 2 1/2" collector header for my 99 gs-r and i need to no what i should do about putting it on. should i just get a flange welded on to fit the header? should i get a high flow cat? or should i get a test pipe? and if i get a test pipe or high flow cat am i going to get any check engine light codes? will it mess the o2 sensor up to make it throw codes? thanks for any help!

 

I have a test pipe on my car and it doesnt throw any codes. But I will give you a warning, it is LOUD, so be prepared. But I would recommend it, I could feel a difference with it in compared to the stock cat (thats with aftermarket exhaust and header already though).

 

but your car is still obd1 i think . 99's are obd2 and you willl get a code. but it wont hurt anything , not a big deal , mine has been on for almost 2yrs now . and its healthier than it ever was.
you will need a 2.5 flange, and i would suggest a test pipe for max gains . . . it wont be that much louder, but will be louder.

 

yeah i found a test pipe for 45 bucks shipped with a 2.5 flange on it on testpipe.com thanks for the help i think im going to get a test pipe!!