Gutting your pre cats
07-19-2011, 08:31 PM
#1
Gutting your pre cats
--------------------------------
I’ve started this thread hoping to make it little easier for anyone planning on gutting their pre-cats... whether it’s for a rattle, or perhaps for an inexpensive power gain to save on some headers.
The first thing you want to do is take your OEM y-pipe heat shields off. A few of the bolts on mine were real rusty so i used a wiz wheel to cut them off as i knew i wasn't going to put them back on. Proceed to take your y pipe bolts that bolt to the 3rd (main) cat, and the bolts that go to the bottom of the front and rear bank pre cats, then drop the Y.
There are bolts on top of the rear bank pre cat; I think two were 12mm and one was 13mm for some reason. You’re going to need some really long swivel extensions (and a drop light to see) to get at these bolts.
Now the rear bank pre cat fought us whole time. We put it in a bench vise and used an air chisel to blast the mesh out of the rear pre cat which IS A WICKED PITA. I suggest using an air chisel which is longer than the cat itself so that you can punch in one end and out the other. The one we had was a little shorter than the cat and it was so tough to get out that he chiseled a crack in side of the pre cat. We welded the **** out of it and it's been fine since.
For the front pre-cat, you’re going to drop it the same way as the rear but it is a lot easier to get to then the rear. When it drops, the ceramic substrate inside can be easily smashed out with a pry bar and a hammer.
Another thing I will say is any bolt you can get some heat on with a torch - do it, because an impact gun will probably snap the bolts.
Bolt the pre cats and your Y-Pipe back on and enjoy. Use an 02 sim to take care of your newly acquired SES light, because you’re going to get a bank 1 and bank 2 catalyst efficiency codes for the 02's.
In the end, it was worth it for me. I got rid of the rattle, gained power and got that nice header gurgle. I hope this made it easier for anyone planning to do this, and if you don't have a mechanical background and/or the right tools (meaning air and heat), I wouldn't recommend it. Go to a trusted mechanic.
I’ve started this thread hoping to make it little easier for anyone planning on gutting their pre-cats... whether it’s for a rattle, or perhaps for an inexpensive power gain to save on some headers.
The first thing you want to do is take your OEM y-pipe heat shields off. A few of the bolts on mine were real rusty so i used a wiz wheel to cut them off as i knew i wasn't going to put them back on. Proceed to take your y pipe bolts that bolt to the 3rd (main) cat, and the bolts that go to the bottom of the front and rear bank pre cats, then drop the Y.
There are bolts on top of the rear bank pre cat; I think two were 12mm and one was 13mm for some reason. You’re going to need some really long swivel extensions (and a drop light to see) to get at these bolts.
Now the rear bank pre cat fought us whole time. We put it in a bench vise and used an air chisel to blast the mesh out of the rear pre cat which IS A WICKED PITA. I suggest using an air chisel which is longer than the cat itself so that you can punch in one end and out the other. The one we had was a little shorter than the cat and it was so tough to get out that he chiseled a crack in side of the pre cat. We welded the **** out of it and it's been fine since.
For the front pre-cat, you’re going to drop it the same way as the rear but it is a lot easier to get to then the rear. When it drops, the ceramic substrate inside can be easily smashed out with a pry bar and a hammer.
Another thing I will say is any bolt you can get some heat on with a torch - do it, because an impact gun will probably snap the bolts.
Bolt the pre cats and your Y-Pipe back on and enjoy. Use an 02 sim to take care of your newly acquired SES light, because you’re going to get a bank 1 and bank 2 catalyst efficiency codes for the 02's.
In the end, it was worth it for me. I got rid of the rattle, gained power and got that nice header gurgle. I hope this made it easier for anyone planning to do this, and if you don't have a mechanical background and/or the right tools (meaning air and heat), I wouldn't recommend it. Go to a trusted mechanic.
Last edited by 036mtmax; 07-20-2011 at 12:34 PM.
07-20-2011, 06:11 AM
#5
Nice write-up, OP!
BronxSleeper has a good point... edit the post and separate the talking points into paragraphs so it's read-able. (Hang on... I'll PM you something.) His other point about headers is OT and typical, so brace yourself for all the header Fan Boys that will surely chime in.
I'm having my pre-cats gutted next week, intending to address my own mystery rattle, and will print this out for my mechanic to chew on before he tackles the job.
Thanks!
BronxSleeper has a good point... edit the post and separate the talking points into paragraphs so it's read-able. (Hang on... I'll PM you something.) His other point about headers is OT and typical, so brace yourself for all the header Fan Boys that will surely chime in.
I'm having my pre-cats gutted next week, intending to address my own mystery rattle, and will print this out for my mechanic to chew on before he tackles the job.
Thanks!
Last edited by Rochester; 07-20-2011 at 07:14 AM.
07-20-2011, 06:34 AM
#7
Sorry about all the clutter but i just flew through it..And as far as the header thing...I gutted my cats for a rear bank pre cat rattle in the first place.. when i noticed the sound difference and apparent power gain i put it on the dyno for kicks and made just as much and in some cases more power than people who have similar mods with cattman or obx headers..Why spend the money if you don't have too.
07-20-2011, 06:40 AM
#8
07-20-2011, 06:42 AM
#9
You've certainly created a buzz for me regarding next week's project. All I was looking for was the most cost-effective way to get rid of this mind-numbing rattle. However, if I can deepen the exhaust tone and add a little extra grunt... that would be nice.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
07-20-2011, 05:56 PM
#10
You've certainly created a buzz for me regarding next week's project. All I was looking for was the most cost-effective way to get rid of this mind-numbing rattle. However, if I can deepen the exhaust tone and add a little extra grunt... that would be nice.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
Hope this helps and thanks for the help on cleaning up the thread...
07-21-2011, 10:19 AM
#12
You've certainly created a buzz for me regarding next week's project. All I was looking for was the most cost-effective way to get rid of this mind-numbing rattle. However, if I can deepen the exhaust tone and add a little extra grunt... that would be nice.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
I'll swing back around here after the job and add my 2-cents from the experience.
Thanks again, 036mtmax.
and thanks for the thread 036mtmax.. though i am a visual learner for sure
07-21-2011, 10:32 AM
#13
07-21-2011, 11:28 AM
#16
I gutted mine it was a b1tch to get all the **** inside out and but taking it all off no problem but the pre cat material that where all the time is, getting Cattman headers but got to get another Max before they arrive.....
07-21-2011, 11:56 AM
#17
it's impossible to replicate sound in real life from a camera to a pc but ill try to do my best.I took these two vids on the dyno but it sounds kind of crappy because it was on my call phone but you can kinda get the idea
Last edited by 036mtmax; 07-21-2011 at 07:22 PM.
07-21-2011, 11:59 AM
#18
Sorry to hear about your max man but at least you were ok and your getting another one
07-21-2011, 12:20 PM
#19
Stats we might be interested in about his car.
1st run hot. hp 240.2@6278 tq 240.0@4007
2nd run hot. hp240.4@6385 tg239.3@4172
3rd run cool hp247.6@6126 tq248.5@3964
mods are gutted pre catts,test pipe,cattman 3'',nwp bop,stillen short ram
1st run hot. hp 240.2@6278 tq 240.0@4007
2nd run hot. hp240.4@6385 tg239.3@4172
3rd run cool hp247.6@6126 tq248.5@3964
mods are gutted pre catts,test pipe,cattman 3'',nwp bop,stillen short ram
Last edited by nishfish871; 07-21-2011 at 12:24 PM.
07-21-2011, 12:24 PM
#20
Not sure but it can't be that much of a difference..If it was 10 more i would have put 260 to the ground on a mustang dyno and i doubt that would have happened with just breather mods and no tune....Anyone want to donate a set of cattman headers so we can find out lol
07-21-2011, 01:51 PM
#22
I had my friend do it for me for 100 bucks and i detailed his truck so idk but if could do it over i would buy a set of used pre cats and gut them first and then when you drop the old ones you have no down time..if you do that id say 2 hours..
07-21-2011, 02:01 PM
#23
I still haven't found the motivation to drop the rear. I'm not looking forward to the actual gutting process for that one. I will say that there is definitely a lot more grunt with the front gutted. I won't speak to performance gains because I have no repeatable data, but I'm glad to know you do. This may be the extra motivation I need to finally gut the rear. 
07-21-2011, 02:05 PM
#24
Senior Member
Join Date: Dec 2008
Location: NYC
Posts: 1,787
07-21-2011, 02:16 PM
#25
It's awesome that you provided this information for everyone. It took me about 2 hours to do the front. I dropped the manifold with it, because I was sloppy and snapped a stud. That was back in February. I still haven't found the motivation to drop the rear. I'm not looking forward to the actual gutting process for that one. I will say that there is definitely a lot more grunt with the front gutted. I won't speak to performance gains because I have no repeatable data, but I'm glad to know you do. This may be the extra motivation I need to finally gut the rear.
I still haven't found the motivation to drop the rear. I'm not looking forward to the actual gutting process for that one. I will say that there is definitely a lot more grunt with the front gutted. I won't speak to performance gains because I have no repeatable data, but I'm glad to know you do. This may be the extra motivation I need to finally gut the rear. Thanks man all i can tell you with exhaust work is that heat is your friend
....you will gain a deeper exhaust note and more power if you drop the rear because it is more restrictive than the front cat.I wish i dyno'd before and after.
07-21-2011, 02:22 PM
#26
Well I hit up Maxboy about doing a custom SRI for me and he said he didn't do them anymore...so I'm not sure if it's jus that he doesn't do or if he just doesn't do anything Maxima related since he got the BMW 
I'm going to a shop later and see what price quote they give me...if I have to spend anything upwards of $250 for the work I want done I might as well put that money towards my headers and get rid of the precats all together...this was just a hopefully cheaper alternative to fix my precat problem and still have money left over to get my catback
I'm going to a shop later and see what price quote they give me...if I have to spend anything upwards of $250 for the work I want done I might as well put that money towards my headers and get rid of the precats all together...this was just a hopefully cheaper alternative to fix my precat problem and still have money left over to get my catback
07-21-2011, 02:37 PM
#27
07-21-2011, 03:18 PM
#28
07-21-2011, 03:26 PM
#29
Wow that's quite suprising how much power it laid down still on the stock manifolds, seems like a cheap easy mod for some extra ponies.
But I still think you would have laid down higher numbers with headers
But I still think you would have laid down higher numbers with headers
07-21-2011, 03:42 PM
#30
07-21-2011, 03:55 PM
#31
Senior Member
Join Date: Dec 2008
Location: NYC
Posts: 1,787
Well I hit up Maxboy about doing a custom SRI for me and he said he didn't do them anymore...so I'm not sure if it's jus that he doesn't do or if he just doesn't do anything Maxima related since he got the BMW
I'm going to a shop later and see what price quote they give me...if I have to spend anything upwards of $250 for the work I want done I might as well put that money towards my headers and get rid of the precats all together...this was just a hopefully cheaper alternative to fix my precat problem and still have money left over to get my catback
I'm going to a shop later and see what price quote they give me...if I have to spend anything upwards of $250 for the work I want done I might as well put that money towards my headers and get rid of the precats all together...this was just a hopefully cheaper alternative to fix my precat problem and still have money left over to get my catback
Even if Maxboy doesn't want to the work, maybe his dad can do it since he owns an exhaust shop. That sucks that he didn't want to do the SRI work.
07-21-2011, 04:06 PM
#32
This damn thread has me jazzed up for a little extra HP, and that's not what I set out to do. You guys...
036mtmax, where did you get your O2 SIM, and how did you choose to wire it in? And did you leave the sensors in, or pull them out and cap?
07-21-2011, 04:21 PM
#33
Originally Posted by RodsMax
I gutted mine. It was (labor intensive) to get all the (substrate) inside out, but taking it off was no problem. The pre cat material--that's where all the time is spent
Originally Posted by 036MT
Now the rear bank pre cat fought us whole time. We put it in a bench vise and used an air chisel to blast the mesh out of the rear pre cat which IS A WICKED PITA. I suggest using an air chisel which is longer than the cat itself so that you can punch in one end and out the other. The one we had was a little shorter than the cat and it was so tough to get out that he chiseled a crack in side of the pre cat. We welded the **** out of it and it's been fine since.
07-21-2011, 04:44 PM
#35
SSIM. Sure about that, are you?
This damn thread has me jazzed up for a little extra HP, and that's not what I set out to do. You guys...
036mtmax, where did you get your O2 SIM, and how did you choose to wire it in? And did you leave the sensors in, or pull them out and cap?
This damn thread has me jazzed up for a little extra HP, and that's not what I set out to do. You guys...
036mtmax, where did you get your O2 SIM, and how did you choose to wire it in? And did you leave the sensors in, or pull them out and cap?
07-21-2011, 04:47 PM
#36
That would be interesting to see what kind of power you could put down on the stock manifolds
07-21-2011, 05:14 PM
#37
o2sim.com is the best place to get one but it looks like they are not accepting orders now for some reason. And I don't remember how I wired mine in since it's been a while but I just left my sensors plugged in and tucked them underneath the engine cover that way they still pick up heat so you won't throw a heater code...
Manny sold me an old, unused SIM from years ago. It's pretty backyard-electronics, but if it works it works. 036mtmax, where'd you get your sim?
Last edited by Rochester; 07-21-2011 at 05:28 PM.
07-21-2011, 05:44 PM
#38
07-21-2011, 07:05 PM
#40
Not sure if it does or not but the front bank precat seems to be the one that always fails on the VQ35's..it is ceramic and crumbles pretty easy..Im going to have to side with KRZ3550"s theory on that one