Stock downpipe catalyst removal

[Used2be]

I finally made the decision to get a flash tune and have decided to go catless. Not so much for more power, but just because it seems wrong to try to make horsepower through such a restriction. It's against my sensibilities for an internal combustion engine.

I know at least one member has gutted his stock DPs, years ago I think, and even though I was dreading it, there was nothing to lose if it didn't work. I'd just buy an aftermarket set, for $700+! I'm not leasing my M5, and Michigan doesn't have smog checks, so hopefully I'll never need the cats.

The removal is much easier than I thought it would be and I don't see any reason these won't be as effective in producing horsepower as an aftermarket pair. The honeycomb material is easily drilled and once you gut the center of both the primary and secondary layers, it's easy to tap a long screwdriver through the remaining material, breaking the circular structure. Then it's easy to pull the pieces out of the DP.

You see in the picture a piece of the broken honeycomb on the left. The primary layer is 3 3/8" thick and the secondary is 2 3/8". They're both wrapped with the white material which is between the smooth back of the catalyst and the DP. I'd thought the catalyst would be bonded to the DP, but it comes out leaving just a smooth metal surface which I try to show in the pictures.

We know these fit with no wiring or sensor problems, and that takes the worry out of it for me. Plus, they're double walled on the turn down the firewall for better heat control. I wonder if the larger open space immediately after the turbocharger helps with spooling? Another positive aspect of using the stock DPs? Hope this is informative and more of you take advantage of a free catless DP instead of paying the exorbitant aftermarket costs.

[apsuard]

Originally Posted by Used2be

I finally made the decision to get a flash tune and have decided to go catless. Not so much for more power, but just because it seems wrong to try to make horsepower through such a restriction. It's against my sensibilities for an internal combustion engine.

I know at least one member has gutted his stock DPs, years ago I think, and even though I was dreading it, there was nothing to lose if it didn't work. I'd just buy an aftermarket set, for $700+! I'm not leasing my M5, and Michigan doesn't have smog checks, so hopefully I'll never need the cats.

The removal is much easier than I thought it would be and I don't see any reason these won't be as effective in producing horsepower as an aftermarket pair. The honeycomb material is easily drilled and once you gut the center of both the primary and secondary layers, it's easy to tap a long screwdriver through the remaining material, breaking the circular structure. Then it's easy to pull the pieces out of the DP.

You see in the picture a piece of the broken honeycomb on the left. The primary layer is 3 3/8" thick and the secondary is 2 3/8". They're both wrapped with the white material which is between the smooth back of the catalyst and the DP. I'd thought the catalyst would be bonded to the DP, but it comes out leaving just a smooth metal surface which I try to show in the pictures.

We know these fit with no wiring or sensor problems, and that takes the worry out of it for me. Plus, they're double walled on the turn down the firewall for better heat control. I wonder if the larger open space immediately after the turbocharger helps with spooling? Another positive aspect of using the stock DPs? Hope this is informative and more of you take advantage of a free catless DP instead of paying the exorbitant aftermarket costs.

Exactly what I was looking to do. Thanks for the write up.

[apexlocator]

Great job! I should have gone this route in hind sight. Curious how it'll sound, as all catless setups I've heard have that crackling roar at WOT.

[Lerxst M4]

Originally Posted by Used2be

I finally made the decision to get a flash tune and have decided to go catless. Not so much for more power, but just because it seems wrong to try to make horsepower through such a restriction. It's against my sensibilities for an internal combustion engine.

I know at least one member has gutted his stock DPs, years ago I think, and even though I was dreading it, there was nothing to lose if it didn't work. I'd just buy an aftermarket set, for $700+! I'm not leasing my M5, and Michigan doesn't have smog checks, so hopefully I'll never need the cats.

The removal is much easier than I thought it would be and I don't see any reason these won't be as effective in producing horsepower as an aftermarket pair. The honeycomb material is easily drilled and once you gut the center of both the primary and secondary layers, it's easy to tap a long screwdriver through the remaining material, breaking the circular structure. Then it's easy to pull the pieces out of the DP.

You see in the picture a piece of the broken honeycomb on the left. The primary layer is 3 3/8" thick and the secondary is 2 3/8". They're both wrapped with the white material which is between the smooth back of the catalyst and the DP. I'd thought the catalyst would be bonded to the DP, but it comes out leaving just a smooth metal surface which I try to show in the pictures.

We know these fit with no wiring or sensor problems, and that takes the worry out of it for me. Plus, they're double walled on the turn down the firewall for better heat control. I wonder if the larger open space immediately after the turbocharger helps with spooling? Another positive aspect of using the stock DPs? Hope this is informative and more of you take advantage of a free catless DP instead of paying the exorbitant aftermarket costs.

I mean seriously, why wouldn't we just gut an OEM set we can pick up on eBay on the cheap (or our stock set)?

Are we really getting that much more power out of a catless set of aftermarket DP's?

This post makes perfect sense to me.

[apsuard]

How long did it take to gut the downpipes?

[135Hoser]

Just fyi, should you ever want to go back to stock, the stock cats retail for about $1600/side.

[jairomvp182]

Originally Posted by 135Hoser

Just fyi, should you ever want to go back to stock, the stock cats retail for about $1600/side.

i see many sets on ebay for under $350

[josec70]

OP, no sensor issues as in no CEL? How's the gas smell? Thanks.

[Lerxst M4]

Originally Posted by jairomvp182

i see many sets on ebay for under $350

That's what I'm saying - pick up one of those cheap sets from eBay and gut those. We know there aren't any fitment issues.

[jairomvp182]

i agree, now i will like to know if there is any gain, or even if the check engine will come on?

[Used2be]

I was very tentative with this first attempt and it was about a two hour process. I will be doing the second one today and I imagine one hour of work to get it done.

I am very aware of the costs of replacement. I used to live in California and I wouldn't have done this without having a spare stock set to fall back on. Michigan is totally different and I feel confident I'll have no regrets. If I had a stock set of DPs to sell right now, the price just went up.

I haven't even ordered the flash tune yet, but I can't imagine the sound or smell change from this type of catless DP would be any different than from the aftermarket types. Without a flash tune I'm sure there would still be a CEL. I'm sorry I'm not a dyno type and don't have a base dyno run to compare, and probably won't even do a post tune dyno after the flash.

[jairomvp182]

it will be very nice if you could to show any improvement over fully stock vs no cats, if you could just do 2 dyno pulls before the tune, will be awesome

[Used2be]

Originally Posted by jairomvp182

it will be very nice if you could to show any improvement over fully stock vs no cats, if you could just do 2 dyno pulls before the tune, will be awesome

That would be awesome, so if you could bring me some DPs with the cats in them, install them for me along with the unflashed DMEs which are waiting to be shipped, I could give you a comparison. And then take it all apart for me, that would be great!

I just did the second DP and it was about half an hour now that I know what I'm working with.

Many others have done before and after pulls, I'm sure you can find results with a search. I don't see any reason the stock DPs with the cats removed would be any different. The shapes and dimensions are so close to a non-stock DP, it has to be a wash.

I like that I have the confidence that the upper O2 sensor is in the air stream in the proper location for an accurate reading. I've read that is important even with a tune, maybe especially with a tune.

[RPiM5]

Indeed, the only reason I went aftermarket Downpipes way back when is that I wanted to keep my stock Downpipes just in case.

Gutting the stock ones will probably net you the same benefits as going aftermarket, but with the added guaranteed protection of the double walled design. However, aftermarket Downpipes that are not double walled but with ceramic coating and/or heat wrap is effective as well for those who intend on keeping their stock Downpipes intact.

Good to have some reports on just simply gutting the stock pipes though.

[jairomvp182]

Originally Posted by Used2be

That would be awesome, so if you could bring me some DPs with the cats in them, install them for me along with the unflashed DMEs which are waiting to be shipped, I could give you a comparison. And then take it all apart for me, that would be great!

I just did the second DP and it was about half an hour now that I know what I'm working with.

Many others have done before and after pulls, I'm sure you can find results with a search. I don't see any reason the stock DPs with the cats removed would be any different. The shapes and dimensions are so close to a non-stock DP, it has to be a wash.

I like that I have the confidence that the upper O2 sensor is in the air stream in the proper location for an accurate reading. I've read that is important even with a tune, maybe especially with a tune.

i get that you already did the second one, what i wanted to say with the 2 pulls was to dyno it just with the modified dp before the tune to actually see how they add up, i know there is plenty of before and after but not the way you are doing it.

[ARC550]

Very nice!!!

[Lerxst M4]

Just picked up one of three sets from eBay for $300. I'll gut those and keep my stockers stock.

[TheHouseWon]

Eddybro and allmotor_2000 had theirs gutted, too

[TheHouseWon]

Originally Posted by Lerxst M6

Just picked up one of three sets from eBay for $300. I'll gut those and keep my stockers stock.

Going to sound NICE with AWE exhaust

[Lerxst M4]

Originally Posted by TheHouseWon

Going to sound NICE with AWE exhaust

I can't wait!

Definitely will have BPMSport turn off cold start when I go to stage 2.

[BPMSport]

Good idea and much more cost effective

The double walled design is much better to use as it keeps heat in check at the rear two cylinders.

[TheHouseWon]

^^And fitment is perfect, not like some aftermarket ones (including mine)