cats in downpipes or have secondary high flow cats

[BMW135iCA]

When I think about the exhaust, I think a few things. First I think how restrictive the downpipes are and was thinking of getting high flow catted downpipes, but also you want the cats further from the turbos for more performance. Now I am thinking of getting catless downpipes and having high flow secondary cats. Where would you guys keep the cats, in the downpipes or the secondary cats?

Chris

[BMW135iCA]

No one has an opinion on this?

Chris

[crzy4135i]

Originally Posted by BMW135iCA

No one has an opinion on this?

Chris

You have to make a choice between what's available to buy unless you plan on having something fabricated. I've only been under my car one time and don't recall the exact exhaust layout. If I wanted to void my warranty I'd get the riss racing catted downpipes for $900.

http://rissracing.com/product_info.php?products_id=1

I would not want the hassle of going with catless downpipes. Getting rid of the pre-cats is the majority of the performance gain. Besides the environmental argument, any shop or the dealership could easily report you for not having catalytic converters. Not to mention the warranty issues.

My 135i will remain stock besides Dinan software. The main reason I bought the car was to have a warranty for a change..

[BMW135iCA]

I don't think they would void your warantee for downpipes unless it was the direct cause of the car's problems. I work at a BMW dealership in sales and I am not as worried about that as some people would be with warantee. I don't want to my car to stink of exhaust though, so that's why i want to keep some catalytic conveter in the car.

Chris

[E82tt6]

If you want to keep smell down, catless DPs with secondary cats in place is the way to go.

You'll get a lot more performance this way than keeping stock DPs and deleting secondaries.

[ktdw]

I don't have any smell with catless DPs, but am worried that I will have it if I remove my secondary cats. I'm looking forward to upgrading to a HFC and a better flowing exhaust. Maybe Borla, since the CPE design removes the secondary cats.

[crzy4135i]

Originally Posted by BMW135iCA

I don't think they would void your warantee for downpipes unless it was the direct cause of the car's problems. I work at a BMW dealership in sales and I am not as worried about that as some people would be with warantee. I don't want to my car to stink of exhaust though, so that's why i want to keep some catalytic conveter in the car.

Chris

Aftermarket downpipes could be blamed for turbos going bad, even if they blew for some other reason. I guess it depends on your particular service manager, etc. My luck isn't that good. Must be nice to work at the dealership.

[crzy4135i]

Originally Posted by ktdw

I don't have any smell with catless DPs, but am worried that I will have it if I remove my secondary cats. I'm looking forward to upgrading to a HFC and a better flowing exhaust. Maybe Borla, since the CPE design removes the secondary cats.

Yea, I ran my S4 with no cats and the exhaust smelled like raw fuel at idle. It wasn't black smoke or anything but you could definitely smell the difference.

[gargoyal]

Originally Posted by BMW135iCA

I don't think they would void your warantee for downpipes unless it was the direct cause of the car's problems. I work at a BMW dealership in sales and I am not as worried about that as some people would be with warantee. I don't want to my car to stink of exhaust though, so that's why i want to keep some catalytic conveter in the car.

Chris

The 135, like most cars today have 2 cats. A near engine and one under the car. In most cases removing the near engine cat (which I believe is the one in the downpipe) will not cause problems or "stink" . It will fail visual smog inspection (if they can see it), but most of the time you can pass the emissions test (don't know if this is true for the 1er yet).

I would be more concern about the faking out of the o2 sensor when removing the near engine cat. I am not sure yet how the ECU uses this data with the turbos. Catless downpipe + a piggyback unit add too many unknowns for me right now. Riss DP (with the high flow cat) is your best if you are going to chip it also. If you are not going to chip it you may not need the second cat.

[BMW135iCA]

I would chip the car before anything, maybe v3. The tune would taker care of the o2 sensor, so no concerns there. I mean I do know that having no cats in the downpipes would probably be better for performance, how much I'm not sure but it should.

Chris

[Riss Racing]

Originally Posted by BMW135iCA

Where would you guys keep the cats, in the downpipes or the secondary cats?

Chris

Keep the secondarys. If your gonna remove a cat always remove the primarys. This will yield the highest gains.