Gutting your pre cats
07-28-2011, 07:59 AM
#82
Warp Speed I believe. http://www.warpspeedperformance.com/nissan.htm
Not sure if they are still selling them as the site looks outdated.
Not sure if they are still selling them as the site looks outdated.
07-28-2011, 12:10 PM
#83
If I'm understanding the explanation from my mechanic accurately (or accurately enough)... feel free to correct me if this doesn't make sense. But he was curious about what the O2 Sim was doing, so he started measuring things. The front O2 sensors create a signal with two distinctly separate extents... like a pulse. And the rear O2 sensors create a signal with a more steady, uniform variance. As long as the signal from the rear sensors are within the range defined by the front O2 sensors, then the ECU is happily assuming the exhaust has passed through the catalyst.
This explains why we need the O2 sensors, even with headers or gutted pre-cats.
That, and there's also an exhaust temperature sensor piggybacked into the O2's, and that still needs to be satisfied. (Yes? No?)
This explains why we need the O2 sensors, even with headers or gutted pre-cats.
That, and there's also an exhaust temperature sensor piggybacked into the O2's, and that still needs to be satisfied. (Yes? No?)
07-28-2011, 12:21 PM
#84
Sexier Than Simpson
Join Date: Apr 2007
Location: Buffalo/Alden, NY
Posts: 1,683
The temp sensor is the key. The O2 sim just puts out a voltage constant and the downstream needs to be less than the upstream. Theoretically you could just build one yourself for all the sensors which would send voltage in the correct ranges and the ECU would be satisfied. The temp sensor is important afaik
07-28-2011, 02:18 PM
#85
Car is back. Pre-cats are gutted. O2 Sim is installed and functioning. At idle and mid-range, the car is a little bit louder, not a lot. The tone got a little bit deeper, for sure. And at WOT, the car is a LOT louder. 
Go figure.
Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
However, the noise remains.
This project was a swing and a miss.
I'm very frustrated right now.
Go figure.Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
However, the noise remains.
This project was a swing and a miss.I'm very frustrated right now.
07-28-2011, 02:36 PM
#86
Car is back. Pre-cats are gutted. O2 Sim is installed and functioning. At idle and mid-range, the car is a little bit louder, not a lot. The tone got a little bit deeper, for sure. And at WOT, the car is a LOT louder. Go figure.
Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
However, the noise remains. This project was a swing and a miss.
I'm very frustrated right now.
Go figure.Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
However, the noise remains.
This project was a swing and a miss.I'm very frustrated right now.
07-28-2011, 02:36 PM
#87
Car is back. Pre-cats are gutted. O2 Sim is installed and functioning. At idle and mid-range, the car is a little bit louder, not a lot. The tone got a little bit deeper, for sure. And at WOT, the car is a LOT louder. Go figure.
Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
Go figure.Off the line and throughout the mid-range, power feels normal. However, at WOT in the upper-range, there is definitely more grunt. Not enough to wet your pants, but it's noticeable and pretty cool.
07-28-2011, 02:38 PM
#88
Well that sucks about the rattle.guess i know replacing my precat is not going to get rid of the rattle but i do hope it cures the sluggishness.Im glad you were straight foward about the increase in noise level that is why im just going to replace and not gut the unit.with these two problems im having currently it has really got me running in circles now that it did not fix your rattle.what else is in that area that could make such a noise?Could something be loose inside the Y-pipe or can it be something to do with the front splash shields i just dont know.The mic i was using picked it up loud and clear i even remember the db level of the noise.at this point i may just start removing parts until the noise goes away.
07-28-2011, 03:29 PM
#90
Either way, this is all first impression stuff. Like any mod, a fair assessment takes a few days and a few runs.
We'll figure that out tomorrow. I'm guessing 3 hours labor. He's usually overly fair to me, and on the flip-side I like to make sure he gets fair payment for his time.
07-28-2011, 04:21 PM
#92
Test pipe/ cattman/ bop/Sri /gutted cats heat soaked run on mustang dyno with g35 wheels im sure it ads more than a bop.compare my dyno to the people that have cattman headers and similer mods.it's right around the same give or take.
07-28-2011, 04:32 PM
#93
Of course, I'm pulling this reasoning out of my dookie.
I'll admit that freely. People with better mechanical knowledge will surely chime in, as well as people who think they have engineering know-how, but have only recently learned to shave.
07-28-2011, 04:41 PM
#94
036mtmax, aren't exhaust efficiencies more relevant near the point of combustion, as opposed to down-the line? In other words: headers > catback, and so on. See, I already had a Cattman Y-pipe configured for the last 3 years. It's possible that gutting the pre-cats was more incremental for me than it was for you.
I'm going to remain optimistic and assume he's fairly accurate in his assessment. 
It's not our fault it took us thirty years to grow facial hair. Don't judge!
07-28-2011, 04:43 PM
#95
good ish mang... i hate seeing **** dyno's... n you think by now ppl would stop... i kinda figure they gave a decent gains... those gains are similar to headers mang... welp rochester... cant say i havent tried staring you towards the OBX but i hope u get everything the way you want
07-28-2011, 04:44 PM
#96
When i found out you had a y i was thinking the same thing but the only way to really tell is for me to get a y and re-dyno the car and see the difference i guess..But mine may be a bit louder because where i have the stock y i do have a test pipe where you have a cat so idk ?? Sorry to hear that that didn't take the rattle out...
07-28-2011, 05:03 PM
#97
I took the car out ramping just now, back and forth on the highway in various gears, speeds, and revs. My second impression reinforces the first, which is that the car is slightly louder, however the tone is certainly deeper. For me, a deeper tone to the exhaust is pleasant, and one of the reasons I love my uneven-length y-pipe.
As for added power... it's all in the upper range, and while noticeable, it's not that big of a change (for me). Still, a power-mod is a power-mod, and it goes in my sig. "Gutted pre-cats"
Now to get back to my mystery rattle, and to do so in another thread, because then I'm off-topic.
Good thread, 036mtmax. Thank you. Hope you don't mind that I whored it so much.
As for added power... it's all in the upper range, and while noticeable, it's not that big of a change (for me). Still, a power-mod is a power-mod, and it goes in my sig. "Gutted pre-cats"
Now to get back to my mystery rattle, and to do so in another thread, because then I'm off-topic.
Good thread, 036mtmax. Thank you. Hope you don't mind that I whored it so much.
07-28-2011, 05:19 PM
#98
I took the car out ramping just now, back and forth on the highway in various gears, speeds, and revs. My second impression reinforces the first, which is that the car is slightly louder, however the tone is certainly deeper. For me, a deeper tone to the exhaust is pleasant, and one of the reasons I love my uneven-length y-pipe.
As for added power... it's all in the upper range, and while noticeable, it's not that big of a change (for me). Still, a power-mod is a power-mod, and it goes in my sig. "Gutted pre-cats"
Now to get back to my mystery rattle, and to do so in another thread, because then I'm off-topic.
Good thread, 036mtmax. Thank you. Hope you don't mind that I whored it so much.
As for added power... it's all in the upper range, and while noticeable, it's not that big of a change (for me). Still, a power-mod is a power-mod, and it goes in my sig. "Gutted pre-cats"
Now to get back to my mystery rattle, and to do so in another thread, because then I'm off-topic.
Good thread, 036mtmax. Thank you. Hope you don't mind that I whored it so much.
Thanks Rochester..glad you like it..hey btw where did you get your sims from ??
07-28-2011, 06:01 PM
#99
036MT: Dude, try the spacers first! $20 solution > $100 solution.
Rochester: At what RPM does your rattle occur and have you had your mechanic take off the heat shield and drive around to see if it's still present? Courtesy has two different heat shields, a "front driveshaft" heat shield and an "exhaust manifold cover", for $45 and $30, respectively.
Most people with heat shield rattle just take them off, but I figure that keeping as much as possible out from the rest of the engine bay is a good thing. And, knowing how you roll, you'd never just lop a part off and run without it.
Rochester: At what RPM does your rattle occur and have you had your mechanic take off the heat shield and drive around to see if it's still present? Courtesy has two different heat shields, a "front driveshaft" heat shield and an "exhaust manifold cover", for $45 and $30, respectively.
Most people with heat shield rattle just take them off, but I figure that keeping as much as possible out from the rest of the engine bay is a good thing. And, knowing how you roll, you'd never just lop a part off and run without it.
07-28-2011, 06:09 PM
#100
036mtmax dynoed with gutted cats. He stated that, ceteris paribus, his gutted cats have similar gains to headers. I haven't seen enough comparison dyno's to substantiate this, but he did have some nice values. Although, I don't recall seeing a control run without the gutted cats either. I'm going to remain optimistic and assume he's fairly accurate in his assessment.
It's not our fault it took us thirty years to grow facial hair. Don't judge!
I'm going to remain optimistic and assume he's fairly accurate in his assessment. It's not our fault it took us thirty years to grow facial hair. Don't judge!I just wish i had dyno'd the car before i did the pre cats so i could have seen exactly how much it made.All i know is theres a couple guys with more mods...headers being one of them and im still putting down the same or more power..im not bragging im just being the test dummy i usually am as an example thats all.
07-28-2011, 06:11 PM
#101
Of course, I'm pulling this reasoning out of my dookie. I'll admit that freely. People with better mechanical knowledge will surely chime in, as well as people who think they have engineering know-how, but have only recently learned to shave.[/quote]
Oh, man. If that aint classic Rochester!
I'll admit that freely. People with better mechanical knowledge will surely chime in, as well as people who think they have engineering know-how, but have only recently learned to shave.[/quote]Oh, man. If that aint classic Rochester!
07-28-2011, 06:12 PM
#102
I just wish i had dyno'd the car before i did the pre cats so i could have seen exactly how much it made.All i know is theres a couple guys with more mods...headers being one of them and im still putting down the same or more power..im not bragging im just being the test dummy i usually am as an example thats all.
07-28-2011, 06:22 PM
#103
If I'm understanding the explanation from my mechanic accurately (or accurately enough)... feel free to correct me if this doesn't make sense. But he was curious about what the O2 Sim was doing, so he started measuring things. The front O2 sensors create a signal with two distinctly separate extents... like a pulse. And the rear O2 sensors create a signal with a more steady, uniform variance. As long as the signal from the rear sensors are within the range defined by the front O2 sensors, then the ECU is happily assuming the exhaust has passed through the catalyst.
This explains why we need the O2 sensors, even with headers or gutted pre-cats.
That, and there's also an exhaust temperature sensor piggybacked into the O2's, and that still needs to be satisfied. (Yes? No?)
This explains why we need the O2 sensors, even with headers or gutted pre-cats.
That, and there's also an exhaust temperature sensor piggybacked into the O2's, and that still needs to be satisfied. (Yes? No?)
The 2 upstream 02's are the most important as they control fuel. The downstream are not as important but they do have a function.
When exhaust goes through the manifolds and pass the upstream o2's they take a "reading" and convert that reading onto a voltage. That voltage is compared to the voltage after the precats which also take a reading of the same exhaust gas but which has passed through the precat. If the precat is functioning correctly the voltages should be different. If the upstream and downstream voltages are in specification you will not throw codes. But if either the upstream voltages are out of spec or too close tothe downstream voltages, then you will throw a code or two.
07-28-2011, 06:42 PM
#104
[quote=Eirik;8139573]036MT: Dude, try the spacers first! $20 solution > $100 solution.
036MT: Dude, try the spacers first! $20 solution > $100 solution.
are you talking about you lost me there Try spacers for what i just put spacers in on sunday and what solution are you talking about...im not having a problem with my car right now
036MT: Dude, try the spacers first! $20 solution > $100 solution.
are you talking about you lost me there Try spacers for what i just put spacers in on sunday and what solution are you talking about...im not having a problem with my car right now
07-28-2011, 06:44 PM
#105
07-28-2011, 07:33 PM
#106
I was in the right thread at the right time, is all.
It's got a little green LED embedded inside the plastic to let you know it's functioning.
And now I've got this thing tucked under my engine cover, LOL.
Last edited by Rochester; 07-28-2011 at 07:36 PM.
07-28-2011, 07:36 PM
#107
I wonder if he would be nice enough to sell me his track v1's
doubt it though
07-28-2011, 07:40 PM
#108
07-28-2011, 07:57 PM
#109
Can't wait to hear how you make out John. Unfortunately I don't think we'll ever know for sure what the presise cause was, but I am sticking to my suspicions about y-pipe restriction causing the whistle, I'm 80% sure the noise will be gone.
07-28-2011, 08:04 PM
#110
http://forums.maxima.org/5th-generat...ml#post8139730
07-28-2011, 08:29 PM
#111
Interesting I somehow missed the last page of this thread completely when I posted that. I'll tag along in your thread. Pity, I was quite sure I had it pegged in the exhaust due it the inability to locate a specific point (noise bouncing/echoing)
But this same effect could be apparent in the intake or other areas. Could be the main cat even. Over to the new thread I go....
But this same effect could be apparent in the intake or other areas. Could be the main cat even. Over to the new thread I go....
07-28-2011, 10:55 PM
#112
07-29-2011, 10:46 AM
#113
Driving around today over familiar routes, playing with the car and getting a feel for the new normal. I'm thinking to myself that the new, deeper rumble is really quite nice. And the extra grunt after the tach climbs over 4K... that's pretty nice, too.
No regrets.
No regrets.
07-29-2011, 12:31 PM
#114
Senior Member
Join Date: Apr 2011
Location: Ontario, Canada
Posts: 539
Good to hear Rochester. I'm just waiting for my Cattman y-pipe to come and I'm gonna gut the pre cats when I have it apart. Pretty pumped for as I have recently done nap spacers and bop and was very happy with the result of those. I will post the results
07-29-2011, 01:26 PM
#115
If it had fixed the rattle, which was the reason I went down this road in the first place, then it would have been totally worth it. As it is... eh, not so much. I mean, I've got a pleasant tone to the exhaust and some upper-end gains, so at least something good came out of it.
Again, no regrets. Well, not serious ones, at least.
08-01-2011, 09:08 AM
#116
BTW do you ever keep track of your gas mileage? I'd like to see if the gutting of the useless-after-20-minutes precats will show any improvement in mileage.
08-01-2011, 09:25 AM
#117
If I had to make a guess, I'd say between 0.5 and 1.0 MPG increase. But just like Republican economic theory, I base that on nothing what-so-ever.
Last edited by Rochester; 08-01-2011 at 09:32 AM.
08-01-2011, 12:16 PM
#118
08-01-2011, 12:24 PM
#119
Didn't drive the car for the last 3 days, however today I took it out for some errands... and I'm liking the new tone and the new grunt more and more.
At first blush, unrealistic expectations were there in the corners of my mind, even though I knew better... and so, the reality was kind of ho-hum. But a few days later, there is a gradual and growing appreciation for the subtle changes attributed to gutting the pre-cats in my config, and I like it.
I like it a lot.
At first blush, unrealistic expectations were there in the corners of my mind, even though I knew better... and so, the reality was kind of ho-hum. But a few days later, there is a gradual and growing appreciation for the subtle changes attributed to gutting the pre-cats in my config, and I like it.
I like it a lot.
Last edited by Rochester; 08-01-2011 at 01:21 PM.