I have a 91 import swb TT.Both my down pipes have rusted through,i'm not looking to spend loads and i already have 2 stainless back boxes and crossover pipes.There is a small pipe that branches from each downpipe if anyone can confirm what they go to?can they be bypassed etc as many downpipes i'm seeing don't have these?Any info would be greatly accepted my car sounds like a tank and feul economy is even worse :(

the small pipe that branches if am thinking about the one your talking about is for aiv and yes you can get rid of it and block the pipe up or remove the whole thing there are some bit of it behind the wheel arch liner and a few more pipes in the engine bay you can remove the lot of just block the pipe up like a half a job but still works

here is a guide I used when I removed mine

http://www.nicoclub.com/archives/remove-the-air-injection-valves-aiv.html

here is a guide I used when I removed mine

http://www.nicoclub.com/archives/remove-the-air-injection-valves-aiv.html

 

cool your a star,so after i do that i'm free to choose what ever downpipe/center section i wish as long as its for the TT?i presume it make no difference if its an auto?not sure on how big the transmission is on a manual and if they get in the way?

the bit were the little pipes are you are talking about and want to change in the cats so you need to pic if you want to remove the cats or not also watch you get one that fits a swb not a lwb am not sure what parts on the system are different from swb and lwb am sure some one can come on a tell you this .the auto box is bigger than the manual box people do fit decats on lwb cars with a auto box but you need to do a little bit of pipe bending to get it to clear the auto box am not sure if that's the same on swb it prob is the same but like I said some one will come on soon and tell you . yes as for once you have removed the aiv of just bloacked the pipe you can fit decats or cat the aiv was removed by Nissan on later models just a load of junk and most people delete it a long with many other deletes

just had a look the decats will fit both swb and lwb cars so you can order a decat set like one from jap speed I do have a decat here that will bold rite on to your down pipes and will clear the auto box I was going to use it but am fitting different pipes now

this will fit its just the back of the system on the swb that is different http://www.ebay.co.uk/itm/JAPSPEED-NISSAN-300ZX-1990-1996-TWIN-TURBO-STAINLESS-STEEL-DECAT-DOWNPIPES-/150772561681?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item231abeb711

here is others who have asked the same thing in the past http://www.300zx.co.uk/forums/showthread.php?163265-do-swb-decats-front-pipes-fit-a-LWB&highlight=swb+decats

i did message the japspeed exhaust people after following your link to ebay but they said manual cars only?not sure if they are saying this because thats what it says in their price guide or if it actually doesn't fit,i'm likely to trust people on this site as knowledge from these pages has served me well in the past?thanks for the link and replies though :)