Installing Header with 2.5 “ collector to a STOCK cat

I am planning to buy a 4-1 header with 2.5” collector for my 99 GSR. At this point, I am not planning to change the CAT ( I know its restrictive but I can not change the stock cat because of the STS class I am running in Auto-x)

1- How can I connect a header with 2.5 “ collector to a stock CAT on a 99 GSR
2-Can a “Braided spacer” like the one below, be used for connecting to stock
CAT?

3-Can I buy anything to “merge” the 2.5” collector to the stock CAT? Can a muffler shop be able to weld this?

Thanks a lot

Btw any one used these jdm 4-1 headers
http://cgi.ebay.com/ebaymotors...=WDVW

https://honda-tech.com/zerothread?id=1078644

 

basically with the collector and spacer, that will take up all of the space of the cat, and that setup will just bolt onto your catback. So you will be running no cat with that setup. The spacer is not a catylitic converter, that is just a straight through piece, no restrictions. In order for it to be a cat, it would need restrictor plates, which can be seen when looking into the cat (look like catacombs).

 

in the auction it says that this can be attached to the cat?
http://cgi.ebay.com/ebaymotors...=WDVW

 

That braided spacer might connect to the collector and bolt to the cat, but you may have to move the stock cat back quite a bit and shorten your exhaust piping. Assuming you are getting an ITR style 4-1, the runners and collector take up quite a bit of space, and putting in that spacer will take up even more, so you would have to move the cat, but it should work if you need to run it for STS as long as the o2 sensor wires are long enough, and that braided spacer is tapered from 2.5 to 2 inches and uses a flange that will bolt to the stock cat.

Before getting the braided spacer, you should contact kteller8 or smsp on H-T and find out if they can make you a custom spacer with flanges that tapers from 2.5 to 2, and take up the least space possible. Then you would only have to bolt it on, move your cat back a bit and have a section of your midpipe hacked off.