Disclaimer
The community here at 355nation.net urges you to please use caution and seek professional assistance when performing modifications to your vehicle. Before attempting any modification it is advised that you refer to your Colorado or Canyon service manual or contact a certified mechanic as not all GMT355 trucks are the same. The staff and the associated members are in no way responsible for any damages, injuries or other harm inflicted to your vehicle or yourself which may result in attempting these modifications. The posts and content presented on this site reflect in no way the views of 355nation.net or it’s ownership.
![Image]()
A 355nation How To presented by
Canyon08Z71
Project Name
Exhaust Manifold Catalytic Converter Deletion
Project Description
This write up will walk you through removing a major restriction on the I4 and I5 exhaust system. This modification has been dyno proven to unleash 10+ horsepower on the I5 motor. Depending on your proficiency and working conditions, prepare to invest 2-6 hours on this project. There are two gaskets on the part of the exhaust system you will be dealing with and both are reusable. To be safe, I would recommend ordering at least the donut gasket before the project but that is up to you. I had both gaskets on hand but did not need them; they were less than $20 for both at GM.
Skill Level
Moderate
Project Vehicle
Make: GMC
Model: Canyon
Year: 2004
Engine: 3.5L
Power windows: Yes
Sun Roof: No
Tools Needed
Mask, protective glasses, and gloves (esp. during catalyst material removal)
3/8” Drive Ratchet
3/8" Drive Shallow and Deep Socket Sets
3/8” Drive 2” Extension
3/8" Drive Breaker bar
½” Drive Ratchet (used for collector nuts)
½” Drive Shallow and Deep Socket Sets
½” Drive Universal Joint Extension
½” Drive 8" extension
½” Drive 4" extension
½” Drive Breaker bar
8mm Socket
10mm Socket (deep and shallow)
13mm Socket (deep and shallow)
15mm Socket (deep and shallow)
Standard and Metric Wrench Sets
Wire wheel or Dremel with sanding disc
7/8” open end wrench or O2 socket
2’ Pry bar
2’ Flat head screwdriver
Air compressor w/ high-pressure output line/fitting attachment
Anti-seeze
Project Time
2-6 hours
Project Cost
Effort, Possbily Small Materials/Tools Cost
Dyno graphs courtesy of JLAUDIO29.
Before:
![Image]()
After:
![Image]()
Manifold Removal
![Image]()
![Image]()
1. Disconnect MAF and O2 sensors. (Unclip harness)
2. Remove intake and intake heat shield and all associated equipment. (8mm,10mm,13mm deep/shallow for K&N FIPK)
3. Remove transmission dipstick. Unlock and pull the dipstick 3 inches out of the tube before removing from transmission. (1- 10mm nut)
4. Remove manifold heat shield. (4 – 10mm nuts)
![Image]()
5. Loosen and detach manifold collector, remove donut gasket. (3 -15mm nuts)
![Image]()
![Image]()
a. A universal joint socket will be required to get at the top nut on the collector due to the front drive shaft interference. Other option is to remove the front drive shaft.
![Image]()
![Image]()
6. Loosen and remove manifold bolts. (9 - 13mm bolts)
a. Secure manifold with your hand during removal of last bolt to prevent it from falling.
7. Remove manifold from truck.
![Image]()
![Image]()
![Image]()
8. Remove O2 sensor from manifold. (7/8” open end wrench or O2 sensor socket)
9. Place manifold in a vice or work on a bench to remove the catalyst material inside the manifold. (2’ pry bar and 2’ flathead screwdriver will be the tools of choice)
a. Use the 2’ pry bar to get into the manifold through the collector to bust up the catalyst material. Use the 2’ flat head screwdriver to bust up the top end of the catalyst material.
![Image]()
10. Once complete with the catalyst material removal. Use compressed air to clean out the manifold of debris left behind.
11. Take a wire wheel to the manifold (where it mates to the cylinder head) and clean it up so the gasket can seat properly.
12. Use compressed air to clean up and debris left behind inside the manifold.
13. Install O2 sensor back onto manifold.
OPTIONAL:
When the manifold is off the truck you may decide to port the exhaust manifold.
A trip to the machine shop or some time with a dremel will work to widen the exhaust ports on the manifold.
See pic:
Picture Courtesy of Supermodulation
![Image]()
Manifold Installation
1. Set manifold down into place by the cylinder head.
2. Roll under truck and install donut gasket in the collector and assemble collector and start all three nuts onto the studs. (apply some anti seeze to threads)
3. Move back up to the engine bay and get manifold gasket in hand. Align the manifold and gasket to the head.
4. Install all manifold bolts by hand and hand tighten them all in. (GM recommends a drop of thread locker on the threads. I did NOT use it. I lightly coated them with anti seeze)
a. Verify gasket seated properly and ensure no bolts are going in cross-threaded.
5. Tighten all manifold bolts, using the GM recommended torque patter and torque specs. (See picture for sequence. 15 lb ft GM spec)
I5:
![Image]()
6. Roll back under the truck and tighten manifold collector nuts. (37 lb ft GM spec).
7. Install manifold heat shield (snake O2 sensor wiring back through hole in shield) and tighten down. (18 lb in GM spec) Reconnect O2 sensor wiring harness.
8. Install transmission dipstick tube grommet (if it came out with dipstick) into the transmission. (see pic) Release and pull the transmission dipstick back 3 inches and install the transmission dipstick back into the transmission. (this will require you place it in the general area from up top and finish the rest underneath) Tighten the transmission dipstick bracket down. (111 lb in GM spec)
![Image]()
9. Install air intake and associated components. Reconnect MAF sensor wiring harness.
---------- 2007 3.7L added coverage --------------
Primary Cat Deletion (Gutting) - '07 3.7L Motor
Courtesy SteveOZ71 (2007 3.7L Test)
Tools required: Same as 3.5L
O2 Sensor Non Fouler:
http://www.355nation.net/forum/how-...letins/391-how-exhaust-manifold-catalytic-converter-deletion-10.html#post604260
There really is no need to go into any great detail here, as the installation is pretty much identical to the 3.5L, with only a few differences...so, no point in doing a totally separate "how to" for the 3.7's. I'll just try to mention the points that are necessary.
The most important is the secondary O2 sensor issue. On the '07's, this sensor monitors the primary cat function/efficiency, so you'll have to either relocate it downstream of the secondary cat, so it will have a "job" to do and thus, not throw a cat inefficiency code. You could also disable it with HP Tuners, if you have access to it. Now, if you go the PcmForLess route, just make sure to let them know you're defeating the cat, and they'll make sure it's disabled as part of your tune so you won't get any codes. I had an O2 bung welded in after the secondary cat when I replaced the muffler so that I could relocate the sensor and then use the original bung for my LM1 wideband. For now, though, we just disabled the O2 sensor with HPT.
The 3.7L's have a couple more emissions components than the pre-07 trucks to meet the '07 standards. The air injection system (A.I.R.), to the best of my limited knowledge, pumps air from the airbox through a carbon(?) canister and then injects it into the exhaust manifold via a solenoid valve, which lowers NOX, hydrocarbons, etc. Someone else here may have a better explanation of this system. This valve will need to be removed after removing the dipstick tube, as the tube bracket mounts to the left-hand stud for the valve. Pre-'07 models simply have a blank-off plate where this valve mounts. The only other thing is that the cat is a bit larger than the 3.5's, according to XHR Customs, and after seeing comparison pics-- it definately is. So it may take a bit longer removing the material on the '07+ trucks. I'm really not sure if GM up'd the cat sizing for the 2.9L, or not....haven't seen a comparo. For me, removing the catylist material was the most time-consuming part of the project.
I recommend wearing a mask as long as you can stand it. It was in the upper 90's when me and my brother did mine, so the mask was used on and off. I also recommend long sleeves, mainly due to the fiberglass you'll be dealing with. I tried not to have any direct contact with the material, but still managed to break out with a nasty rash on my left arm after gutting the cat.
The results: On a scale of 1 - 10.....I have to give it a 10, simply because it's a free mod (other than a little time and sweat) and the performance increase is definitely there, as shown with JLAUDIO29 's dyno sheets. I ran the truck hard for a few runs directly after this job and then loaded the new tune, as I wanted to see the difference of just this mod w/o adding any tuning. The truck ran noticeably harder throughout the entire rpm range. After we loaded the tune, I took her for a few more hard runs. I am very pleased with the result.
The only real downside I can think of is the weird hollow, tinny sound emitted at idle and light throttle. I immediately thought I had an exhaust leak upon firing it up the first time. Everyone seems to have this sound, described one way or another. I can't say if it's more pronounced with the 3.7's or not, since the cat is larger, and I haven't heard anyone else's truck with the 3.5 for comparison. Other than that, I'd say it simply gives the overall exhaust note a slightly deeper tone, inside and outside the cab.
The community here at 355nation.net urges you to please use caution and seek professional assistance when performing modifications to your vehicle. Before attempting any modification it is advised that you refer to your Colorado or Canyon service manual or contact a certified mechanic as not all GMT355 trucks are the same. The staff and the associated members are in no way responsible for any damages, injuries or other harm inflicted to your vehicle or yourself which may result in attempting these modifications. The posts and content presented on this site reflect in no way the views of 355nation.net or it’s ownership.
A 355nation How To presented by
Canyon08Z71
Project Name
Exhaust Manifold Catalytic Converter Deletion
Project Description
This write up will walk you through removing a major restriction on the I4 and I5 exhaust system. This modification has been dyno proven to unleash 10+ horsepower on the I5 motor. Depending on your proficiency and working conditions, prepare to invest 2-6 hours on this project. There are two gaskets on the part of the exhaust system you will be dealing with and both are reusable. To be safe, I would recommend ordering at least the donut gasket before the project but that is up to you. I had both gaskets on hand but did not need them; they were less than $20 for both at GM.
Skill Level
Moderate
Project Vehicle
Make: GMC
Model: Canyon
Year: 2004
Engine: 3.5L
Power windows: Yes
Sun Roof: No
Tools Needed
Mask, protective glasses, and gloves (esp. during catalyst material removal)
3/8” Drive Ratchet
3/8" Drive Shallow and Deep Socket Sets
3/8” Drive 2” Extension
3/8" Drive Breaker bar
½” Drive Ratchet (used for collector nuts)
½” Drive Shallow and Deep Socket Sets
½” Drive Universal Joint Extension
½” Drive 8" extension
½” Drive 4" extension
½” Drive Breaker bar
8mm Socket
10mm Socket (deep and shallow)
13mm Socket (deep and shallow)
15mm Socket (deep and shallow)
Standard and Metric Wrench Sets
Wire wheel or Dremel with sanding disc
7/8” open end wrench or O2 socket
2’ Pry bar
2’ Flat head screwdriver
Air compressor w/ high-pressure output line/fitting attachment
Anti-seeze
Project Time
2-6 hours
Project Cost
Effort, Possbily Small Materials/Tools Cost
Dyno graphs courtesy of JLAUDIO29.
Before:
After:
Exhaust Manifold Catalytic Converter Deletion
Manifold Removal
1. Disconnect MAF and O2 sensors. (Unclip harness)
2. Remove intake and intake heat shield and all associated equipment. (8mm,10mm,13mm deep/shallow for K&N FIPK)
3. Remove transmission dipstick. Unlock and pull the dipstick 3 inches out of the tube before removing from transmission. (1- 10mm nut)
4. Remove manifold heat shield. (4 – 10mm nuts)
5. Loosen and detach manifold collector, remove donut gasket. (3 -15mm nuts)
a. A universal joint socket will be required to get at the top nut on the collector due to the front drive shaft interference. Other option is to remove the front drive shaft.
6. Loosen and remove manifold bolts. (9 - 13mm bolts)
a. Secure manifold with your hand during removal of last bolt to prevent it from falling.
7. Remove manifold from truck.
8. Remove O2 sensor from manifold. (7/8” open end wrench or O2 sensor socket)
9. Place manifold in a vice or work on a bench to remove the catalyst material inside the manifold. (2’ pry bar and 2’ flathead screwdriver will be the tools of choice)
a. Use the 2’ pry bar to get into the manifold through the collector to bust up the catalyst material. Use the 2’ flat head screwdriver to bust up the top end of the catalyst material.
10. Once complete with the catalyst material removal. Use compressed air to clean out the manifold of debris left behind.
11. Take a wire wheel to the manifold (where it mates to the cylinder head) and clean it up so the gasket can seat properly.
12. Use compressed air to clean up and debris left behind inside the manifold.
13. Install O2 sensor back onto manifold.
OPTIONAL:
When the manifold is off the truck you may decide to port the exhaust manifold.
A trip to the machine shop or some time with a dremel will work to widen the exhaust ports on the manifold.
See pic:
Picture Courtesy of Supermodulation
Manifold Installation
1. Set manifold down into place by the cylinder head.
2. Roll under truck and install donut gasket in the collector and assemble collector and start all three nuts onto the studs. (apply some anti seeze to threads)
3. Move back up to the engine bay and get manifold gasket in hand. Align the manifold and gasket to the head.
4. Install all manifold bolts by hand and hand tighten them all in. (GM recommends a drop of thread locker on the threads. I did NOT use it. I lightly coated them with anti seeze)
a. Verify gasket seated properly and ensure no bolts are going in cross-threaded.
5. Tighten all manifold bolts, using the GM recommended torque patter and torque specs. (See picture for sequence. 15 lb ft GM spec)
I5:
6. Roll back under the truck and tighten manifold collector nuts. (37 lb ft GM spec).
7. Install manifold heat shield (snake O2 sensor wiring back through hole in shield) and tighten down. (18 lb in GM spec) Reconnect O2 sensor wiring harness.
8. Install transmission dipstick tube grommet (if it came out with dipstick) into the transmission. (see pic) Release and pull the transmission dipstick back 3 inches and install the transmission dipstick back into the transmission. (this will require you place it in the general area from up top and finish the rest underneath) Tighten the transmission dipstick bracket down. (111 lb in GM spec)
9. Install air intake and associated components. Reconnect MAF sensor wiring harness.
---------- 2007 3.7L added coverage --------------
Primary Cat Deletion (Gutting) - '07 3.7L Motor
Courtesy SteveOZ71 (2007 3.7L Test)
Tools required: Same as 3.5L
O2 Sensor Non Fouler:
http://www.355nation.net/forum/how-...letins/391-how-exhaust-manifold-catalytic-converter-deletion-10.html#post604260
There really is no need to go into any great detail here, as the installation is pretty much identical to the 3.5L, with only a few differences...so, no point in doing a totally separate "how to" for the 3.7's. I'll just try to mention the points that are necessary.
The most important is the secondary O2 sensor issue. On the '07's, this sensor monitors the primary cat function/efficiency, so you'll have to either relocate it downstream of the secondary cat, so it will have a "job" to do and thus, not throw a cat inefficiency code. You could also disable it with HP Tuners, if you have access to it. Now, if you go the PcmForLess route, just make sure to let them know you're defeating the cat, and they'll make sure it's disabled as part of your tune so you won't get any codes. I had an O2 bung welded in after the secondary cat when I replaced the muffler so that I could relocate the sensor and then use the original bung for my LM1 wideband. For now, though, we just disabled the O2 sensor with HPT.
The 3.7L's have a couple more emissions components than the pre-07 trucks to meet the '07 standards. The air injection system (A.I.R.), to the best of my limited knowledge, pumps air from the airbox through a carbon(?) canister and then injects it into the exhaust manifold via a solenoid valve, which lowers NOX, hydrocarbons, etc. Someone else here may have a better explanation of this system. This valve will need to be removed after removing the dipstick tube, as the tube bracket mounts to the left-hand stud for the valve. Pre-'07 models simply have a blank-off plate where this valve mounts. The only other thing is that the cat is a bit larger than the 3.5's, according to XHR Customs, and after seeing comparison pics-- it definately is. So it may take a bit longer removing the material on the '07+ trucks. I'm really not sure if GM up'd the cat sizing for the 2.9L, or not....haven't seen a comparo. For me, removing the catylist material was the most time-consuming part of the project.
I recommend wearing a mask as long as you can stand it. It was in the upper 90's when me and my brother did mine, so the mask was used on and off. I also recommend long sleeves, mainly due to the fiberglass you'll be dealing with. I tried not to have any direct contact with the material, but still managed to break out with a nasty rash on my left arm after gutting the cat.
The results: On a scale of 1 - 10.....I have to give it a 10, simply because it's a free mod (other than a little time and sweat) and the performance increase is definitely there, as shown with JLAUDIO29 's dyno sheets. I ran the truck hard for a few runs directly after this job and then loaded the new tune, as I wanted to see the difference of just this mod w/o adding any tuning. The truck ran noticeably harder throughout the entire rpm range. After we loaded the tune, I took her for a few more hard runs. I am very pleased with the result.
The only real downside I can think of is the weird hollow, tinny sound emitted at idle and light throttle. I immediately thought I had an exhaust leak upon firing it up the first time. Everyone seems to have this sound, described one way or another. I can't say if it's more pronounced with the 3.7's or not, since the cat is larger, and I haven't heard anyone else's truck with the 3.5 for comparison. Other than that, I'd say it simply gives the overall exhaust note a slightly deeper tone, inside and outside the cab.
