[Jmore92]

How's it going guys I'm debating if I should gut my cats on my 335i or not. Car is full bolt on minus down pipes and exhaust ATM running on e50. I'll will be replacing the turbos with RB 1s and stock location inlets for a mild performance increase and to simply replace the work turbos.

I would love to do 3" downpipes but living in CA I just don't want to have to deal with smog, to my knowledge with a downpipe fix I can get the ecu in readyiness state correct? And by them having to physically check for catalyst converters I will be in the clear. Having to revert the intake and chargepipe is an easy trade off. But in not looking to change the downpipes every time. The intercooler is basically invisible.

So has anyone gutted their oem cats? It's really just to fly under the radar, and plus I'm sure my cats are pretty bad with the amount of miles they currently have I want to avoid any possible issues.

[mweisdorfer]

Originally Posted by Jmore92

How's it going guys I'm debating if I should gut my cats on my 335i or not. Car is full bolt on minus down pipes and exhaust ATM running on e50. I'll will be replacing the turbos with RB 1s and stock location inlets for a mild performance increase and to simply replace the work turbos.

I would love to do 3" downpipes but living in CA I just don't want to have to deal with smog, to my knowledge with a downpipe fix I can get the ecu in readyiness state correct? And by them having to physically check for catalyst converters I will be in the clear. Having to revert the intake and chargepipe is an easy trade off. But in not looking to change the downpipes every time. The intercooler is basically invisible.

So has anyone gutted their oem cats? It's really just to fly under the radar, and plus I'm sure my cats are pretty bad with the amount of miles they currently have I want to avoid any possible issues.

I don't know if anyone that has gutted cats. If you do get Catless downpipes, look into MMP, they have a deal for $250.00. ARM also have good quality items with a high ROI. However, I wouldn't do relocation inlets. You are better off putting your $$ into inlets and outlets coupled with at least a 5" stepped FMIC.

Yes, the DP fix can be used once a year to beat the smog machines. You will blow codes if you don't use a tune like MHD or Cobb, which clear the CEL codes upon startup.

With an FMIC, RB 1's, inlets, outlets, and Catless down pipes coupled with a tune, you'd be well over 425HP. Maybe even over 450 approaching 475.

If they really do look under the car and look at your cats, to make sure you haven't removed them, then look into Cobb high flow cats. They also make a great charge pipe.

[Emilime75]

From my own research, it appears that gutted cats were popular when the N54 was newly released and after market downpipes were either unavailable, or expensive. The consensus is, they do work, but not as well as a down pipe that stays the same diameter the entire length of the pipe. These days, with cheap downpipes that have been proven to work and fit, it doesn't make much sense to go through the trouble of gutting the stock cats. Plus, if you ever run into issues, emissions, want to sell/trade the car, you can swap them back on.

[Jklad]

A lot of The guys in California gut their cats to pass emissions and not have to deal with the hassle of replacing downpipes all the time.

Don't bother...if you search around you'll find that there is no benefit whatsoever to gutting stock DP.

[Aode06]

I gutted my cats, car runs smooth on MHD and performs excellent.

[_N54]

You can get China made down pipes for less than $150 on eBay.

[bimmerguy1210]

Makes no sense to gut cats considering their value and catless dp’s being nearly 1/4 the price of oem dp’s

[mike@x-ph.com]

Originally Posted by bimmerguy1210

Makes no sense to gut cats considering their value and catless dp’s being nearly 1/4 the price of oem dp’s

+1

keep your stock downpipes and buy a set of downpipes from a trusted vendor

[Jaronbwall]

Stock downpipes are valuable, way too much work, quality cat-less DP flow better. Don't waste your time.

[lookalikehuuh]

So I could be crazy here but I have seen tons of report of people with DP Fix having all kinds of weird issues that are nearly impossible to get rid of until dealership reflashes the ECU with updated software.

If I recall one of the leading theories was that because the post cat 02s are used for calibration of the pre cat 02s the ECU would experience all kinds of strange issues because the DP fix could cause those calibration values to go haywire with no real way to reset them quickly.

[R3dLeader]

Originally Posted by lookalikehuuh

So I could be crazy here but I have seen tons of report of people with DP Fix having all kinds of weird issues that are nearly impossible to get rid of until dealership reflashes the ECU with updated software.

If I recall one of the leading theories was that because the post cat 02s are used for calibration of the pre cat 02s the ECU would experience all kinds of strange issues because the DP fix could cause those calibration values to go haywire with no real way to reset them quickly.

Reflashing the DME will wipe out any of those adaptives you speak of.