hollowing out the 3rd cat

[desert]

"As of a couple of years ago GM no longer makes the vehicles 49 state emissions certified, they are now 50 state certified (for California). The last cat in that picture is a cat, it is a unmonitored cat so it can be cut out of the system and wont affect the running of the truck at all since it is not monitored. When GM added them to the 2009 G8 cars the pup cat caused a 5hp change in the rating, so I would assume prob close to that on the truck as well."

 

 

 

Edited June 27, 2014 by desert

[Newm]

Good question....sub'd.

 

You would think it sure would help it breathe better.

[fondupot]

Hmmmm very interesting. Let us know your results!

[iCryWheniGoPoop]

I just removed mine, if there is any change when removing/hollowing out, it would be for the better.

[14'SilveradoLT]

I just removed mine, if there is any change when removing/hollowing out, it would be for the better.

 

Notice any changes in the tune, as far as AFR/knock/timing in your tune?

 

I would assume that the numbers might stay more linear.

[iCryWheniGoPoop]

It did show about 3-4% change in fuel trims but I did my exhaust at the same time so I can only speculate how much it actually helped. I noticed no difference in relieving any of the factory KR by adding the exhaust/removing CaliCat. FYI... Factory calibrations at part throttle are aggressive for 87 octane though.

[14'SilveradoLT]

^^^I was running solely 93 octane but the Shell decided get water in the tanks (so I'm avoiding it) and it went to .30 cents more than 89.

 

I swapped to 89 the knock counts on the stock tunes "okay" for the most part. So, I may run 89 over 93 for a while since I'm still un-tuned.

Edited July 4, 2014 by 14'SilveradoLT

[Cliff14Denali]

How is this done? Did you have to cut the factory pipe to hollow it out or just unbolt cat back? I haven't really looked at the factory system yet.

[desert]

How is this done? Did you have to cut the factory pipe to hollow it out or just unbolt cat back? I haven't really looked at the factory system yet.

Hoist the truck by the frame to allow the suspension to drop. Remove the clamp from your third cat. Pop the rubber exhaust hangers loose with spray lube and large screwdriver. Pull the entire cat-back factory exhaust forward and down while giving it a 1/4 twist. Use a long masonery bit and large screwdriver to gut the 3rd cat. You might want to use a respirator or at least a dust mask. Install the cat-back system of your choice. Enjoy !

 

 

 

 

 

 

Edited July 31, 2014 by desert

[nvrnuf4me]

It did show about 3-4% change in fuel trims but I did my exhaust at the same time so I can only speculate how much it actually helped. I noticed no difference in relieving any of the factory KR by adding the exhaust/removing CaliCat. FYI... Factory calibrations at part throttle are aggressive for 87 octane though.

 

Forgive the ignorance, but by gutting the 3rd cat and re-installing the stock cat back would still make the exhaust a little louder right? Or, would it still be about the same noise level just with better flow?

[jay15892]

I'm wondering if this will wake up my magnaflow dual exhaust? My girlfriends 2013 silverado sounds way better then mine with what is essentially the same kit..

[Luster]

 

Forgive the ignorance, but by gutting the 3rd cat and re-installing the stock cat back would still make the exhaust a little louder right? Or, would it still be about the same noise level just with better flow?

I'm thinkin' louder. I've done it on a couple Corvettes and it sounded WAY better!

[spiGini]

I hollowed mine out but only the center, didn't take it all out of the sides. Wonder if I should go back and take it all out if its creating a disruption in the air flow through the partial hollowed portion.

[Cliff14Denali]

I did mine today and it really don't sound too much louder. I have factory resonator with 3 1/2" diameter magnaflow muffler with no flapper valve. Looks like I will be doing a muffler back setup with a free flow resonator. I want to keep a resonator to eliminate drone.

[J-Jeezy]

gunna attempt this aswell as the airbox mod on monday.. already have the muffler deleted aswell as the flapper valve bolted open. hoping for good results!