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Discussion Starter #1
Finally got my final exhaust mod completed: My 4x4 rear cats replaced with 2 1/2 inch straight flow T-304 SS resonators.

This is a two sided honest to goodness personal opinion/analysis on this mod.

First the positive. There is a slight deeper tone change, slight improvement of throttle response, and marked imrovement in the "looks" department (see links below my SIG to view my exhaust). After examining the OEM 2nd row cats, I was amazed why Nissan even installed these (1st thumbnail) converters. They are only about 2 inches thick (about same size as the widest portion of the cats) and seem to be very fragile. They appear very restrictive (see thumbnails).

And here's the negative: After spending $312 for quality labor and T-304 SS tubing (plus I supplied the resos too), I could have achieved the same performance goal by punching holes into the "honeycomb" cats to open it up, vacumm all the residuals and presto: OEM looking cats functioning as straight pipes (4x4 models only). Since the O2 sensors are upstream, it would have not affected the computer readings anyway. I could have saved myself 400 big ones just for this mod.

Well, everything is done. I have little regrets knowing that knowledge comes after experience and this is one expensive (though good looking) mod that is not worth the cost (only because of the free alternative--removal of the honeycomb catalyst) and using the casing to act as a straight pipe.

I will be adding the "installed" thumbnails in a few days and will also update my website for the entire installation.
 

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For us californians, we can't touch the cats... Or that's what I assume ....

looks good
 

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At least your new resos should be a little lighter than those boat anchor cats! Kind of surprised that just doing these small pipes cost about half as much as the rest of your system though.

Don't forget to update your audio clips!
 

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phillipyang said:
For us californians, we can't touch the cats... Or that's what I assume ....

looks good
You could do what he mentioned and punch the guts out. That way they would only be able to tell if they dismantled your exhaust and looked inside.
 

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Discussion Starter #5 (Edited)
HavockWK said:
At least your new resos should be a little lighter than those boat anchor cats! Kind of surprised that just doing these small pipes cost about half as much as the rest of your system though.

Don't forget to update your audio clips!
True. Those OE cats are heavy.

The difficult (or expensive) part of the install were the multiple "indirect" mandrel bending. There were as many "turns or bends" (though minimal in degree of angle) into this install as the cat-back system previous installed. They count the # of bends. I will update with some audio/video clips after this weekend. Got to attend daughter's graduation from college.
 

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HavockWK said:
You could do what he mentioned and punch the guts out. That way they would only be able to tell if they dismantled your exhaust and looked inside.

Until he goes to pass an emissions test, and FAILS.
 

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wow... good info. your exhaust is a great representation of what the premier exhaust system should look like.

right now as we speak, a local exhaust shop is doing my setup. He is only charging me $50 more to make the 2 straight pipes. not using ss304 piping tho...
 

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Those look more like resonators then CATS to me.
 

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BigBlackTruck said:
Until he goes to pass an emissions test, and FAILS.
I guess if they use a "sniffer" type test. If they just use the plug in type that they use here, it will pass.
 

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Discussion Starter #11 (Edited)
Yomama said:
Those look more like resonators then CATS to me.
The two rusty "missile looking" sections are the OE catalytic converters. What makes me absolutely positive of this, is the presence of the "honeycomb" shaped catalysts that occupies the widest internal part of tube. They are only about 2 inches thick, looks flimsy without real function that their removal (IMHO-and I could be dead wrong) has little or no significant effect to the total exhaust pollutants (4x2s have only the front cats).

There are tons of threads why 4x4s have 2 pairs while 4x2s have one pair of cats and had been discussed and killed a thousand times BUT no clear-cut reason seems to surface. Anyway, in NJ, new cars have 4 years of no emission testing and I hope and pray that when the time (3 more years) comes to have my Titan inspected, the NJ-DMV does not know the difference between the 4x4 & 4x2 exhausts.

I may just try to punch one section out and document with photos just to see how it works.
 

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gr8titan said:
The two rusty "missle looking" sections are the OE catalytic converters. What makes me absolutely positive of this, is the presence of the "honeycomb" shaped catalysts that occupies the widest internal part of tube. They are only about 2 inches thick, looks flimsy without real function that their removal (IMHO-and I could be dead wrong) has little or no significant effect to the total exhaust pollutants (4x2s have only the front cats).

There are tons of threads why 4x4s have 2 pairs while 4x2s have one pair of cats and had been discussed and killed a thousand times BUT no clear-cut reason seems to surface. Anyway, in NJ, new cars have 4 years of no emission testing and I hope and pray that when the time (3 more years) comes to have my Titan inspected, the NJ-DMV does not know the difference between the 4x4 & 4x2 exhausts.

I may just try to punch one section out and document with photos just to see how it works.
First, IF you choose to 'punch out' a catalytic converter, DON'T BREATH THE DUST. It contains heavy metals ( Platinum and Paladium in the oxidation
stage you are taling about). These metals can cause lung damage if inhaled.

Second, that flimsy section is a ceramic honeycomb and is quite strong unless abused. Most last the life of the vehicle without a problem.

Third, It was more than enough to deal with what HC and CO emissions the Titan puts out. Nissan makes a purty darn good engine management system and there really aren't a lot of heavy emissions to deal with on a STOCK Titan.

To be honest, there is every chance your new cat replacement pipes won't flow as much exhaust as the converters you replaced. The way resonators
work, they cause turbulance in the flow and can be quite restrictive.

On the other hand, your new pipes look really cool.

You might try this site for general background on Cats.
http://auto.howstuffworks.com/catalytic-converter.htm/printable
 

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Discussion Starter #14 (Edited)
carteach0 said:
First, IF you choose to 'punch out' a catalytic converter, DON'T BREATH THE DUST. That flimsy section is a ceramic honeycomb and is quite strong unless abused. Most last the life of the vehicle without a problem.
I "punched out" out one of these honeycomb catalyst late today. I secured it on a table vise and using the straight end of a crow bar, punched a hole thru. That sucker crumbled like a dry cookie!!! Total time of removal of catalyst: 5 seconds. It took longer for the dust to settle :clap: :clap:

I've read a few threads regarding noises coming from these downstream catalytic converters and upon examination by the dealership, the honeycomb catalyst have fractured and broken apart and had to wait weeks for a replacement. My personal opinion and suggestion? Knowing what I know now, and having spent hundred of dollars for this mod, I would punch out the catalyst (for a straight pipe benefit) but remove them from the vehicle first as they crumble like dried up cookie! It would be easier to clean up.

I may do a little experiment when I have some free time. Reinstall these punched out cats and see if there is any difference in performance between these and the straight flow resonators I just had installed.

Enclosed are before and after "punch out" photos of the cats
 

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gr8titan said:
I "punched out" out one of these honeycomb catalyst late today. I secured it on a table vise and using the straight end of a crow bar, punched a hole thru. That sucker crumbled like a dry cookie!!! Total time of removal of catalyst: 5 seconds. It took longer for the dust to settle :clap: :clap:

Yup, whack'en 'er with a crowbar counts as abuse... LOL.

Like I said, don't breath the dust. That's what GM warned us techs about AFTER they had us gutting and refilling cats for quite a while. Like they said: "Whoops... we forget to mention thats are bad for you".

The test I would like to see is simple.... using a dyno: HP and torque with factory cats VS straight pipe (not empty cat cans).
I know with many new vehicles the exhaust is so finely tuned that any real change will actually lower horsepower.

As for us, we are looking to exceed the life and utility of our last truck (still in service with my son, a 1991 Chev 1500, 250,000 miles). I don't think I'll be making any performance mods. Maybe when I get to 300K (g).

I AM welding up a rear window protector and hope to have it at the powder coaters next week. I'll also be picking up a tonneau next month.
After that.... some LED light work both inside and out.
 

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BigBlackTruck said:
Until he goes to pass an emissions test, and FAILS.

It will pass either a sniff test or obd II scan test no sweat.

The secondary cats make zero sense to me. If the were upstream of the primary cats it would make sense that they are there for cold start emmisions. Being that they are downstream of the primary cats makes them just about useless. All they will achieve is to retain more heat from the restriction it represents from the secondary cat to the engine, which will in turn increase underhood engine heat and shorten the life expectancy of the engine. Its amazing how much underhood heat is there from the cats alone, the cats produce more underhood heat then the engine itself. With the advent of obd II emissions this has been an increasing issue due to mounting the cat as close to the exhaust port as possible to clean up the exhaust with no regard for the engine itself. Years down the road when the engine harness becomes brittle and breaks apart in your hands as well as coolent hoses failing you can thank the good ole obd II emissions. But what can ya do hehe.
 

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Discussion Starter #18
steves said:
I'm sorry, I just can't get over the humor in using something rusty as a point of reference in photos (since I did the same thing....) :smokingco
What did you do? Make the "rusty" as a point of reference (LOL) or punch out the honeycomb catalysts? If it was the later, any change in your truck's performance?
 

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gr8titan said:
What did you do? Make the "rusty" as a point of reference (LOL) or punch out the honeycomb catalysts? If it was the later, any change in your truck's performance?
No, Sorry....in the pics I posted of how the hitch fits around the exhaust I had said "that rusty piece there..." and the OP used rusty to describe something in his photo.
 

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gr8titan.....could you measure the narrowest point on the cats for me? I thought about gutting my cats (meow!), but it looks like they neck down quite a bit....to 2" or possibly narrower?? I just want to eliminate as much restriction as possible.

I'm still having trouble getting someone to install my 2.5" Dynomax race bullet resos, but I'm hopin' to have it done in the next week or so. If not, I'll probably just gut 'em and call it done!

Thanks for all the info and pics....especially of the internals of the rear cats. I'm tired of hearing over and over how these are not cats, but resos on the 4X4's!

As far as the reason for the rear cats on the 4X4's vs the 4X2's....the only explanation that makes sense to me, is that the 4X4 weighs more so the engine will work a little harder causing more exhaust emissions. I don't think it's enough to fail an emissions test. The primary cats are the same on both models.
 
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