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      03-17-2018, 01:03 PM   #1
hendrira
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330i no cats

Contemplating gutting front and rear cats! I don't mind a CEL and emissions test or inspection is not an issue where I am. I may get a tune later but for now just gutting the cats. My question is will the car run fine without getting a tune. I know the 02 sensors will cause the fuel to run rich but will that be a problem? Thanks guys
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      03-17-2018, 01:33 PM   #2
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Originally Posted by hendrira View Post
I don't mind a CEL and emissions test or inspection is not an issue where I am.
If the CEL is on, (which it will be if you gut the cats) your car is obviously not running right. You'll be sipping fuel like a mf. I would get a tune.
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      03-17-2018, 01:49 PM   #3
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Originally Posted by hendrira View Post
Contemplating gutting front and rear cats! I don't mind a CEL and emissions test or inspection is not an issue where I am. I may get a tune later but for now just gutting the cats. My question is will the car run fine without getting a tune. I know the 02 sensors will cause the fuel to run rich but will that be a problem? Thanks guys
no, your car is not going to run right. it's not even going to run somewhat right. basically, the car will detect that airflow has greatly increased, causing the car to run lean, which will cause the car to compensate by dumping tons of fuel into the combustion chamber. at least 50% of the gains will be achieved by actually tuning the ECU.

plus, gutting the cats is not recommended because the open space where the cats used to be will cause exessive turbulence. I would recommend just getting catless headers and an ECU tune. you can pick up some cheap russian ebay headers (which are actually pretty decent quality especially considering the price) which will perform fine, just be a massive pain in the ass to install correctly. if you are deleting your primary cats, I would advise you leave the secondaries in place to deal with smell. its either one or the other.

for now, I would recommend you go to a muffler shop and just start by removing your secondary cats to hold things down while you save up for your catless headers and ECU tune.
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      03-17-2018, 01:49 PM   #4
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Just keep them. Have you owned a cat less car before? You will smell toxic fumes on you’re clothes hours after driving.

As far as power - you’ll have greater gains going with catless performance catless headers and leaving the rear cats than no cats at all on stock equipment.

You’re going to have to remove the headers anyway. Best just to replace at that point. The stock headers are a terrible design.
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      03-17-2018, 02:43 PM   #5
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Thanks for the advice everyone you are a great help.
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      03-17-2018, 02:58 PM   #6
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Originally Posted by tlow98 View Post
Just keep them. Have you owned a cat less car before? You will smell toxic fumes on you’re clothes hours after driving.

As far as power - you’ll have greater gains going with catless performance catless headers and leaving the rear cats than no cats at all on stock equipment.

You’re going to have to remove the headers anyway. Best just to replace at that point. The stock headers are a terrible design.
agreed. the stock Manifold - not headers are a completely shit design.
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      03-17-2018, 09:39 PM   #7
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agreed. the stock Manifold - not headers are a completely shit design.
Are the exhaust manifold and headers different things? confused
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      03-17-2018, 09:55 PM   #8
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Our cats have 2 sets of o2 sensors, 4 total.
2 before the cat, 2 after the cat, the only ones that matter are the ones before the cat, they measure the mixture of fumes coming out of the motor, as long as they can read those correctly it should be fine, if not then it’d be compensating by making the car run rich or lean. The precat o2’s are what tell the ecu how to run, the rear O2’s are just for emissions
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      03-18-2018, 11:52 AM   #9
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Originally Posted by N52 Moistenor View Post
agreed. the stock Manifold - not headers are a completely shit design.
He's back!

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      03-18-2018, 05:49 PM   #10
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Quote:
Originally Posted by tlow98 View Post
Just keep them. Have you owned a cat less car before? You will smell toxic fumes on you’re clothes hours after driving.

As far as power - you’ll have greater gains going with catless performance catless headers and leaving the rear cats than no cats at all on stock equipment.

You’re going to have to remove the headers anyway. Best just to replace at that point. The stock headers are a terrible design.
Yeah, I think OP did not consider how much work is involved to get to the primary cats. If you're in there and you're not replacing the stock exhaust manifold, you're probably wasting your time.

What's the motivation here anyway? I assume it's either performance or sound improvement. In the case of the first, see above. In the case of the latter, look elsewhere-- deleting catalytic converters won't change the whole character of the exhaust system.
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      03-21-2018, 01:17 AM   #11
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He's back!

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Oh man, was that STR-6IX?!

He fooled me!
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      03-21-2018, 11:53 AM   #12
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He fooled me!
Got me too!
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      03-21-2018, 01:18 PM   #13
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OP, if you want a little extra power and sound (but beware that you might actually be trading some low RPM TQ for high RPM HP), then your best bet for a cheap solution is to have an exhaust shop weld a pipe in place of where your second pair of cats is located on the exhaust front section.

A better solution would be to buy aftermarket headers and replace the exhaust manifolds, which would result in no longer having the first pair of cats.

Neither option REQUIRES a tune, IMO, but a tune would definitely help either option, especially with the header option.

You can delete all the cats, if you'd like, but the car will be loud, probably won't sound all that great, and it may be a little smelly too.
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      03-21-2018, 06:07 PM   #14
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Quote:
Originally Posted by atmosphericM View Post
OP, if you want a little extra power and sound (but beware that you might actually be trading some low RPM TQ for high RPM HP), then your best bet for a cheap solution is to have an exhaust shop weld a pipe in place of where your second pair of cats is located on the exhaust front section.

A better solution would be to buy aftermarket headers and replace the exhaust manifolds, which would result in no longer having the first pair of cats.

Neither option REQUIRES a tune, IMO, but a tune would definitely help either option, especially with the header option.

You can delete all the cats, if you'd like, but the car will be loud, probably won't sound all that great, and it may be a little smelly too.
If he replaces the secondary cats with pipe the same diameter as the stock piping I don’t see why he would lose torque. Seems to me like the scavenging would be better actually than with secondary cats in place.

Edit: according to this deleting secondary cats is good for +9hp and +3tq

http://www.e90post.com/forums/showthread.php?t=703329

I intend to find out for myself how it sounds... I have supersprint secondary cat delete pipes inbound now.

Last edited by Biginboca; 03-21-2018 at 06:48 PM.
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      03-21-2018, 08:08 PM   #15
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Got me too!
i really dont understand what that was all about. bad advice?
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      03-22-2018, 11:27 AM   #16
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Quote:
Originally Posted by Biginboca View Post
If he replaces the secondary cats with pipe the same diameter as the stock piping I don’t see why he would lose torque. Seems to me like the scavenging would be better actually than with secondary cats in place.

Edit: according to this deleting secondary cats is good for +9hp and +3tq

http://www.e90post.com/forums/showthread.php?t=703329

I intend to find out for myself how it sounds... I have supersprint secondary cat delete pipes inbound now.
I agree that you'd think they wouldn't lose TQ. But the only graph I've seen, which granted was with the aFe pipes (that are larger than stock), lost a lot of low end TQ. I wish I could see the dyno graph on that link you posted.. but alas.. noobs and their photobucket.

I too am about to install my Supersprint pipes. If there was a competent dyno shop within 100 miles of me, I'd gladly test them. But alas, Alabama...
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