High boost flutter/surge

[Dennisaliy]

Could I hollow out the stock dp? The cats are toast so I cant resell them. Would it be similar to a aftermarket catless downpipe?

[Dennisaliy]

.

[Camwilson]

Time to go catless.

[Jeff23spl]

the oem pipe size is smaller so it won't flow as well as an aftermarket dp but it will decrease restriction.
To run the car after doing this, one must install an upgraded hpfp and a tune that will lower the wg duty to avoid overboost or you will go fuel cut untill a rod make it's way thru the engine bloc

[Dennisaliy]

Okay, I think I'll gut them because that seems like the most cost effective option. Also its already half done lol

[MSMS3]

As stated above, there are precautions you must take when running catless.

1. You absolutely must have a hpfp upgrade. While not as high flowing as the 3" catless dp/rp as I run, it is substantially higher flowing than you were before). You will exceed the fuel capabilities of the stock hpfp to keep up under load if you don't upgrade. When that happens, you can lean out your AFR and destroy your engine.

2. You will need a tune to run catless. You will encounter nasty spikes up to about 21-22 psi (maybe higher, because the stock map sensor runs out of voltage at 22 psi and will not read higher, even though you may be above that number. A tune consistent with higher exhaust flow will eliminate those spikes. Even the canned Hypertech tune I run safely took care of that and runs like a raped ape with catless exhaust with target and actual boost hitting about 18 psi under maximum load.

3. You will probably get a check engine light for improper temperature in the primary cat. Aftermarket downpipes have a raised 02 sensor bung that changes the sensor location in the exhaust flow. My downpipe has this feature. There are aftermarket screw in 02 sensor extensions you can buy to eliminate the problem. Or, you can get a commonly available spark plug anti-fouler extension and drill a hole in the middle large enough for the sensor probe to stick through. There should be threads here on this subject.

It's not as easy as just knocking the honeycomb out of the cats and rolling. You must increase pump capacity and must address the nasty boost spikes.

Whether you want a permanent check engine light or want to raise the sensor is up to you. I would recommend you address the check engine light, or otherwise, you will be unable to know when you have some other problem that triggers a CEL that needs to be investigated and fixed.

[Dennisaliy]

Originally Posted by MSMS3 As stated above, there are precautions you must take when running catless. 1. You absolutely must have a hpfp upgrade. While not as high flowing as the 3" catless dp/rp as I run, it is substantially higher flowing than you were before). You will exceed the fuel capabilities of the stock hpfp to keep up under load if you don't upgrade. When that happens, you can lean out your AFR and destroy your engine. 2. You will need a tune to run catless. You will encounter nasty spikes up to about 21-22 psi (maybe higher, because the stock map sensor runs out of voltage at 22 psi and will not read higher, even though you may be above that number. 3. You will probably get a check engine light for low temperature in the primary cat. Aftermarket downpipes have a raised 02 sensor bung that changes the sensor location in the exhaust flow. My downpipe has this feature. There are aftermarket screw in 02 sensor extensions you can buy to eliminate the problem. Or, you can get a commonly available spark plug anti-fouler extension and drill a hole in the middle large enough for the sensor probe to stick through. There should be threads here on this subject. It's not as easy as just knocking the honeycomb out of the cats and rolling. You must increase pump capacity and must address the nasty boost spikes. Whether you want a permanent check engine light or want to raise the sensor is up to you. I would recommend you address the check engine light, or otherwise, you will be unable to know when you have some other problem that triggers a CEL that needs to be investigated and fixed.

This is very helpful. Thank you and everyone who has helped me in this thread.

[Fstrnyou]

If you are in a 6 or Gen1 3, just turn off the codes for the secondary O2 when you get tuned...unless you have emissions inspections to pass.