what if we cut off the pre cat and weld in a straight pipe? just read some horror stories on the forum about the pre cat failings and the damage it can cause to the engine.

 

problem number one... that area is not straight lol...

someone.. stillen maybe? used to make a pipe that deleted that front pre cat.. kinda like the one that you car still buy for the cat right before the b-pipe....if you find it let me know.. lol

 

im sure getting a bend on the pipe wont be a problem...

 

has anyone replaced the factory pre cats with a hi flo cat? As in just cut the flange off the existing pre cat pipe and weld it to a an aftermarket hi flo cat

 

that would be pointless, no gains/waste of money and they would probably be too large for that small amount of area.

Straight piece of pipe if anything.

With the VQs they aren't tuned as richly as the QR is, those engines tend to have the issues you talked about with the precats failing and destroying the engine, the VQs don't have this problem, if there is even one

 

now im kinda scared. my pre-cat has been making a rattling sound when you rev the engine for at least 15,000 miles. I never knew there was potential engine damage from this. can anyone verify that a bad precat will destroy a VQ35? if this is the case I guess its time for me to change/gut it.

 

changing out a clogged cat is normal and they do sell replacements for these parts.

Like I said above, I never heard it happening on a VQ but on a QR engine I hear its a severe problem.

 

I am getting the dreaded code after replacing my o2 sensor-white wire. I am wondering if there is a how-to or diagram on how to replace the precat. I am worried about possible engine failure down the road. I thought about the antifouler repair but I have a stock exhaust and read the antifouler bandaids the problem only if you have aftermarket exhaust system.

 

the precats on the 02/03 are known to break down causing the particles to get sucked back in to the cylinder and then causing oil usage. I have this, and its relatively common, if i had known before hand i would have removed the precats since they are pretty much pointless in the first place.

I plan on gutting mine anyway and putting in an o2sim to run my sensors.

 

OBX V2 or Cattman headers would solve all the problems.

 

i think the cheapest route would be to gut the cats and get the o2 sim. Headers would be nice though. i think i may try the gut / o2sim route and see how i like it. i am not looking for any HP gains i am just looking for that damn noise to go away

 

esp since the obx are like 400 shipped (IIRC) its a no brainer..

 

the precats break down over time yes. but there is something else that causes the oil consumption. Although everyone makes a big deal about it, on average 1-2 qt per 3000-5000 miles is what i've heard. Ls1's and LS2's burn just the same and so does the Honda s2000. Just some people make a big deal out of it then others

 

they were cheaper at one point....I love how the ebayers raise the prices when they get a flock of people buying their stuff.

 

wouldnt you?

 

I burned 3 qts under 1k miles and it didn't burn oil before. That's what those precats did for me (oh yeah and the engine went kablooey).

 

im actually interested, is there anybody that did this and dynoed or ran a 1/4??? i would actually like to know... as much as i want that OBX header, i would way rather not using $400 on it

 

id think the gains would be pretty good considering this is a fair restriction going into the y pipe especially if the cat is broken/clogged.

 

I gutted my precats. I don't think you pick up that much. I might of picked up a couple hp. But nothing really noticeable. The car does sound better tho

 

how hard was it to gut them? how long didit take?

 

im thinking ill have the straight pipe welded in, this way even if i needa put the cats back onfor any reason, i can have it welded back in. any idea how much this should roughly cost?

 

+1. I'm also curious how hard this is to do in my driveway. Doesnt look like it'd be too bad. Anyone who's done this-how difficult was the job overall (removal of pre-cat and gutting)

 

Well first. Its not worth welding a pipe. The first attempt didn't go to well. I tried gutting the rear one while it was still on. But it was a brand new solid precat, so i gave up the first day. Next morning i took them both of and it was pretty easy after that. If your precats are old they'll after a few wacks with a hammer. After you finish and everything is back together. You are going to have a CEL. You'll need a o2 sim or spark plug anti-foulers (worked for me) heres a link that'll help http://forums.maxima.org/5th-generat...or-spacer.html

 

so to gut the pre-cat im assuming that all you have to do is unbolt it, smack it with a hammer, and rebolt? I did this to my rear cat, but I have never attempted to touch my pre cat. I ironically just got a cel for my rattleing cat, so I think ill just gut it and O2 sim it so I can still pass NYS inspection

 

Pretty much. I found the front much easier. My rear cat was new but it was rattling. I actually had to drill it till it broke into pieces. But usually they get old and brittle and break up quick.

 

Headers ftw. Just bought mine

 

I just did this pretty easy if your mechanically inclined some of the nuts are tricky to get to but not bad with the right tools. I would like to note that this will make your exhaust louder. I have a megan catback and it made it way more throaty. I was not expecting it to make the exhaust louder it does drone slightly with my catback which I didnt care for but its not that bad. Other than the drone at highway speeds I think it sounds real good.

 

i would love to see a dyno of someone with gutted cats or at least someone who've ran a 1/4 mile time with gutted cats, im really thinking about doing this... any idea on a ball park price for what a mechanic would charge???

 

Any sound clips?

 

why is welding in a pipe not worth it?

 

Thats how a precat looks.. I dont see how you would weld a pipe. Only way to fix is headers or gut it

 

i see, didnt think they looked like that, thanks for the pic! how many hours did it take you to get thisdone? reason i ask is ill probably have a shop do it.did you have to get the cat out with the header? or can you unbolt it seperately

 

It's just as hard as installing headers, but without the hp gains.

 

ahmad im gonna get the o2 sensor extender, looks really simpleto work with, do we just simple install this with the o2 sensor so that it "reads" less emmisions? and i need just 1 right? and what size do i get, there isnt much space in case i get one thats too long. thanks man!

 

will gutting make the exhaust louder if your running the stock exhaust still

 

with the stock muffler i doubt ull notice too much off a difference, there is a long *** resonator on the b pipe.

 

Yea, I used 2 short ones for both. With 1 i still had a CEL. so i had to add a second. Its real tight in the front, but it'll work fine

 

worth it getting just 1 longer one? do the headers have to come of to gut the cat? just wondering what gaskets id need to buy.

 

buy some used 00-01 manifolds, and buy an 01 y-pipe, plug the egr valve...












it would work

 

I did not remove the manifolds. I managed to get the precats off of them.