Secondary Cat Delete

[jclaib7]

Is there any point in doing this? Are there any performance gains or pleasing sounds?

I'm assuming the secondary cats are there due to the SULEV vehicle spec and are not really necessary, much like the carbon filter.

I have the BMW PE and PI and will soon be adding the AA N51 tune or possibly Evolve's new tune. I'm not sure if they can tune for this.

[631twentyeighteye]

According to my mechanic and a few dyno runs(such as Andrey's) there's a 3-5hp to be gained from removing them. My mechanic says BMW mostly uses them to reduce sound volume and suggests removing them for peak performance. I don't think tuning is necessary to capitalize on they're removal, the computer will self adjust as it's ran.

[jclaib7]

Originally Posted by 631twentyeighteye

According to my mechanic and a few dyno runs(such as Andrey's) there's a 3-5hp to be gained from removing them. My mechanic says BMW mostly uses them to reduce sound volume and suggests removing them for peak performance. I don't think tuning is necessary to capitalize on they're removal, the computer will self adjust as it's ran.

That sounds promising. I could probably have my local exhaust guy hack it off and replace it with a straight pipe for $50 bucks.

Is it easily accessibly once on the lift?

[andrey_gta]

Originally Posted by jclaib7

That sounds promising. I could probably have my local exhaust guy hack it off and replace it with a straight pipe for $50 bucks.

Is it easily accessibly once on the lift?

The angle of the replacement pipe needs to be correct, its in a 60 degree angled area.

I suggest you spend time on the forums to understand the 3 stage manifold conversion and the tunes available for headers. Both options will show more gains then just a secondary-cat delete.

The secondary cat delete prevents one from getting headers from SuperSprint or Scheimann or Maplesridge's decat pipes & having the smells contained. Therefore the only choice is the offering from AFE, their 300 cell catted header for n52.

If you want to do the secondary decat, than SuperSprisnt race pipes may be the best option which have a clamp-on ends. A solution, inspired by german 125i's would be to custom fit a 135i midpipe from the n55, or any decat midpipe like maddad, into a muffler.

My exhaust is a full custom 3" exhaust from the exhaust manifold into a 135i muffler. It sounds awesome, aggresive and at the same time civil due to baffled 135i muffler. It complicates my situation with heads, unless custom I fit a race cat in 200 or 300 cells.

[631twentyeighteye]

Originally Posted by andrey_gta

The angle of the replacement pipe needs to be correct, its in a 60 degree angled area.

I suggest you spend time on the forums to understand the 3 stage manifold conversion and the tunes available for headers. Both options will show more gains then just a secondary-cat delete.

The secondary cat delete prevents one from getting headers from SuperSprint or Scheimann or Maplesridge's decat pipes & having the smells contained. Therefore the only choice is the offering from AFE, their 300 cell catted header for n52.

If you want to do the secondary decat, than SuperSprisnt race pipes may be the best option which have a clamp-on ends. A solution, inspired by german 125i's would be to custom fit a 135i midpipe from the n55, or any decat midpipe like maddad, into a muffler.

My exhaust is a full custom 3" exhaust from the exhaust manifold into a 135i muffler. It sounds awesome, aggresive and at the same time civil due to baffled 135i muffler. It complicates my situation with heads, unless custom I fit a race cat in 200 or 300 cells.

For what it's worth, my exhaust still is extremely smelly even with the secondary's in place. Not so much when you're inside the car or driving around, but when i start the car inside my garage and im walking around i can certainly smell the catless headers exhaust.

[andrey_gta]

I get some smells with my Sec-delete in the cold start situation. It is not bad, I imagine a header would be more intense.

[Wakka]

I dont smell anything with my secondaries off. I remember when i took them off they were really clogged up though. I would assume the primaries have the same problem.

[TheSt|G]

Originally Posted by 631twentyeighteye

For what it's worth, my exhaust still is extremely smelly even with the secondary's in place. Not so much when you're inside the car or driving around, but when i start the car inside my garage and im walking around i can certainly smell the catless headers exhaust.

Odd, mine is pretty smell free. I get a little on cold start outside, but it never permeates the car or is noticeable when driving around with windows down, even in traffic.

When my E36 M3 had straight pipes though that was awful.

[631twentyeighteye]

Originally Posted by TheSt|G

Odd, mine is pretty smell free. I get a little on cold start outside, but it never permeates the car or is noticeable when driving around with windows down, even in traffic.

When my E36 M3 had straight pipes though that was awful.

I only can smell it with both windows down when i'm sitting at a light for a few minutes and there's no wind, or in my garage when i'm outside of the car or i have the window open. Other than that it's completely smell free. Though to be honest, i really like the catless smell, I'm used to it from my race quad/dirtbike days. Nothing smells better than a 2 stroke running race gas

[Solo_M_Tech]

Lol I'm curious why our cars are so " smelly" with the cats removed? I deleted the cats on my 02 Camaro SS with long tube headers and custom x pipe and didn't notice any smells.

[jclaib7]

I spoke to my local exhaust shop about deleting the secondary cat and they were concerned about the "legality" of messing around with this component.

Any concerns there?

[Wakka]

It varies from state to state.

[cmcdonald]

Originally Posted by Wakka;*****768

It varies from state to state.

Actually it doesn't. Removing any emissions equipment including either the primary cat or the secondary cat is illegal for the shop to do by federal law if the vehicle will be used on the street. Now states where there are no vehicle inspections, this is not big deal because no one will most likely find out. But it is illegal for the shop to do this in any state. I have encountered plenty of shops who will not do this type of work because if it somehow was to be traced back to them they could potentially be fined or shut down. I think you will have an easier time with getting a shop to say put on cat-less headers than remove the secondaries because the primaries are hard to see in a visual inspection.

[Chandon]

Running catless in Australia is a $10k fine I hear.

[Wakka]

Originally Posted by cmcdonald;*****806

Actually it doesn't. Removing any emissions equipment including either the primary cat or the secondary cat is illegal for the shop to do by federal law if the vehicle will be used on the street. Now states where there are no vehicle inspections, this is not big deal because no one will most likely find out. But it is illegal for the shop to do this in any state. I have encountered plenty of shops who will not do this type of work because if it somehow was to be traced back to them they could potentially be fined or shut down. I think you will have an easier time with getting a shop to say put on cat-less headers than remove the secondaries because the primaries are hard to see in a visual inspection.

I dunno, every shop i went to in tampa said they would happily do the 2ndary, but not the primary.

[TheSt|G]

Originally Posted by Wakka

I dunno, every shop i went to in tampa said they would happily do the 2ndary, but not the primary.

Florida also does not have inspection.

"Custom" work at an exhaust shop will result in rust down the road.

[chris82]

Thread is old but no piont in starting a new one. So what is the verdict here on deleting the secondary cats?

I plan on doing the SS headers at some point (after my next inspection). Should I just leave the secondary cats there and not go through the trouble? Will removing them allow me to get any noticable gains from the SS headers?

[kobeballer96]

Originally Posted by Chrisar82

Thread is old but no piont in starting a new one. So what is the verdict here on deleting the secondary cats?

I plan on doing the SS headers at some point (after my next inspection). Should I just leave the secondary cats there and not go through the trouble? Will removing them allow me to get any noticable gains from the SS headers?

i say do it, going catless might aswell go the whole 9 yards, thats just my opinion doesnt hurt, i can bet the STIG will chime in and say leave the stock 2 secondary cats on because they are factory "highflow cats". People that mod their cars for track setup or all the best stuff and don't even drive them lol.

[TheSt|G]

Originally Posted by Chrisar82

Thread is old but no piont in starting a new one. So what is the verdict here on deleting the secondary cats?

I plan on doing the SS headers at some point (after my next inspection). Should I just leave the secondary cats there and not go through the trouble? Will removing them allow me to get any noticable gains from the SS headers?

Leave them, the difference between having them and not is not something you(people in general) are capable of feeling. With SS headers and straight pipes, your car will noticeably smell.

You drove mine with SS headers and the secondaries still in place, what were your thoughts on odors/power?

[MarkkyyMan]

Originally Posted by TheSt|G

Leave them, the difference between having them and not is not something you(people in general) are capable of feeling. With SS headers and straight pipes, your car will noticeably smell.

You drove mine with SS headers and the secondaries still in place, what were your thoughts on odors/power?

+1, little to nothing will be gained from deleting secondary kitties.

[chris82]

Originally Posted by TheSt|G

Leave them, the difference between having them and not is not something you(people in general) are capable of feeling. With SS headers and straight pipes, your car will noticeably smell.

You drove mine with SS headers and the secondaries still in place, what were your thoughts on odors/power?

Yea I honestly didn't smell anything from your car St|g. As far as power I couldn't tell since I have nothing to compare it against. Definitely faster than mine haha. I think I'll end up keeping them until I get bored again

[2tonik]

So do I understand correctly that having a shop install the SuperSprint headers on a street car would be a Federal violation due to the fact that the primary cats are located in the factory exhaust manifold, thus resulting in the removal of emissions equipment in the eyes of the Feds?

For some reason I was hoping that as long as the car passed emissions, which according to St|g, it should, having the SuperSprint headers installed wouldn't be illegal.

I don't/can't wrench so I suppose I'd have to find a mechanic to do the work "out of the shop" or otherwise off the clock...