Okay, after searching through five pages of exhaust related threads, I decided to make my own.

I just bought a 1997 240SX(base) and the muffler is rusting out due to salt and age.
I'd like to put a newer, slighty more performance minded exhaust on. I like to do things right the first time, so I want to get all my questions answered before I start.

Are there two O2 sensors? I know there's one in the length of pipe between the two catalytic converters, is there another?

Can I get rid of the second(larger) cat without causing a CEL of any other problems?

I plan on getting the HotShot header at some point, does that get rid of the first(smaller) cat that's at an angle coming off the exhaust manifold?

What size is the collector on the HotShot?

If I think of anything else, I'll add it in a later post, but if anyone could answer these questions for me I'd really appreciate it.

 

You're killing me here guys, does no one know their *poop* here or what? Seems all anyone can do is ***** about newbs asking about offset.








Just kidding, but seriously, someone's gotta know this *dookie*.

Edit: Apparently I can't swear. Words have been changed to protect the innocent

 

i can answer part of your questions... the cat issue is this... the first cat (small one) is called a pre cat and in most places it can be removed if you replace the second cat... usually what happens is the pre cat goes bad and trashes the second cat... i would replace both cats with one high flow cat that bolts up to the header...

get the header befor starting the exhaust work... makes things a lot easier when it comes to making custom pipes... not to mention deleting the cats and replacing them with one unit will change the length of the whole exhaust...

i am pretty sure that you have 2 o2 sensors...you cant quote me on this but i am pretty sure there is...

i dont know the collector size so i cant answer that question...

i do have a little bit of advice for you... go with 2.5 inch pipe from the start... there is no reason to have to build the system twice... go with the bigger pipe from the beginning...

 

Thanks Wikd! So no one has had any problems with getting rid of the pre-cat? I don't want to mess up the A/F ratio.

And if I get a universal cat, put it just after the header but before the O2 sensor? How is that going to fit in there?

Does the HotShot come with an O2 bug welded into it, or do I have to extend that O2 sensor somewhere?

Sorry for all the questions, I just want to do it right, and I haven't found my answers anywhere else, so hopefully this thread will help out others.

By the way, I had already settled on 2.5in pipe. I plan on ordering all my mandrel piping from Kteller.com since no one around here does anything but crush bent.

 

I thought the first cat was the actual cat, and the one further down line was just for looks.

In any case, as long as you bolt a cat after the header you'll be OK.

OBDII checks the function of the cat, so it checks the o2 reading before and after the cat to make sure things are working fine. If you don't run a second o2 after the cat, you will trigger a CEL.

I'm not sure of the collector on the HotShot. I have my S13 hotshot downstairs, I'll check it.

-Justin

 

Okay, so the cat that is just after the header is the important one.

Thanks guys, now I just need to look for a place to get the Hotshot for cheap. The best price I've seen so far is $330 including shipping, is there somewhere else I should look?

 

I think the hotshot comes with the hole for the O2 sensor as seen on this pic:

picture of hotshot

and there's a nice cat to go with it:

Nice...yumy

 

Wow, that Hotshot actually has a LOT of holes in it. I know one is for the EGR, one for the O2 sensor, what's the other for?

Edit: looks like there's another on the flange at the bottom of the downpipe too. WTF?

And that cat looks really large, will it fit in place of the tiny stock one? Also, I need 2.5in inlet/outlet.

 

As you can see by the link, its specially desinged for 240's..... what else do you need? it MUST fit there. Besides, if you go to exaust in that website, you see the hotshot and right underneath, the cat, so they must go together. Maybe if you ask the website poeple. And pictures can be decieving. I went to Sonics and ordered that Jr. banana boat. When it came, it was about 3/4 of a regular sized Pc mouse. I thought it would be larger

 

the upper hole is for the egr... the next one down is for the pair valve... the one below that looks like it is for the first o2 sensor... there seems to be one more hole at the end of the collector... but i cant tell to well... the cat looks good tho...

 

Well, it could just be the lower cat, I don't know. Good link though, thanks.

And lol at the Sonic thing, they are way too expensive.