Im in the process of buying a downpipe for my 97 gst and it has a greddy catback system already on it. The ones im looking at on ebay are 2.5 in. inlet and 2.75 in. inlet. What inch inlet and outlet dose my stock downpipe on my car have? This is crutial because i dont want to buy something that wont fit. BTW my cat back system bolts up directly to my stock cat....but with the down pipe it eliminates the cat so i need to make sure its going to measure up with my cat back exhaust too. Any help would be apprecieated.

 

my advice would be to stay away from the ebay downpipes unless you are prepared to do some fabricating. They are usually pretty decently priced but dont fit well and aren't made well. Roadrace sells an excellent downpipe for $200 but I dont think it bolts on to the greddy directly its made for the apex n1. I dont think anyone makes one for the greddy exhaust though. I would go with the roadrace one though, buy a greddy flange and have someone weld it on for you. The pipe is made to fit perfect and uses a quality flex section. A lot of the ebay flex's will break and leak.

 

Another thing to look out for, is even if you are going to buy a 3" downpipe, make sure the o2 housing side before the flex is 2.5 inches. Anything bigger and you wont be able to get the bolts on trust me.