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M2 Technical Topics > N55 Engine / Drivetrain / Exhaust / Bolt-ons / Tuning > Catted Downpipe on Stock Tune

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      10-05-2016, 02:21 AM   #1
SeanWRT
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I am looking to fit a catted downpipe to my m2 and stay with stock tune. At least that's what I figure works best for me.

I take it many recommend against that approach, the primary 3 reasons being:

1) DME will adjust to the freer flow so the power gain is minimized.

2) Stock tune won't take full advantage of it.

3) CEL will be thrown eventually.

On #1, I also heard that BMW turbo engine DME is load based and will not discount the power gain out of a freer flow exhaust. Not sure.

On #2, what does that mean exactly? More specific on the untaken advantages?
I am not pursuing a new high at down low or something, but instead wanting to address the significant TQ tapering down all the way to fuel cutoff, which is seen on many m2 dyno charts due to stock turbo flow limitation.
Specifically, is catted DP's PRESSURE HOLDING capability at upper range compromised with stock tune? To make no mistake, to hold the pressure, I am not asking turbo to work harder.

On #3, to be reasonable, I will accept the cat failure if it's endured heavy usage for years - stock cat can fail under excessive usage too. I'll just buy a new one.

Appreciate someone in the know shed some lights, especially on #1 and #2.
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Last edited by SeanWRT; 10-05-2016 at 03:07 AM..
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      10-05-2016, 12:06 PM   #2
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1. DME probably does adjust for it a little at max load. I ran the Fabspeed catted pipe for a month with no other mods. The midrange increase is more noticeable than the top end.

2. The stock boost taper is to protect the turbo for longevity and to avoid warranty claims. The freer flowing downpipe will allow the turbo to work less hard throughout the rev range. An untuned car misses the benefits of the the more efficient turbo.

3. I've never seen a CEL on mine after several thousand miles. I can't recall anyone else with a quality 200 cell or greater catted pipe getting one either.

Bonus #4. After a very mild tune in conjunction w catted pipe, the car is alive and a rabid beast on the street. The sound improvement alone with the pipe is worth every penny. Please just get a nice catted pipe and never look back. I'll PayPal you 10$ if you're not thrilled after driving!
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      10-05-2016, 02:03 PM   #3
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The stock boost taper is to protect the turbo for longevity and to avoid warranty claims. The freer flowing downpipe will allow the turbo to work less hard throughout the rev range. An untuned car misses the benefits of the the more efficient turbo.
Thanks for sharing your experience.

Turbo is more efficient only when revving lower. Aftermarket tune, if anything, should take advantage of the lower back pressure and raise the boost target, resulting in a harder working turbo.

Instead, stock tune probably will have turbo run at a lower rpm when stock boost target is met earlier with freer flow exhaust. In that case, resulting in a more efficient turbo.

Any tuners chime in?
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      10-05-2016, 03:18 PM   #4
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2/boost will not change without a tune, you will get more power because of high flow cats but it when you tune your car boost will be raised to make even more power

3/ We offer the VRSF CEL delete, it will hide the code without the need of a tune
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      05-12-2017, 04:27 PM   #5
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Quote:
Originally Posted by SeanWRT View Post
I am looking to fit a catted downpipe to my m2 and stay with stock tune. At least that's what I figure works best for me.

I take it many recommend against that approach, the primary 3 reasons being:

1) DME will adjust to the freer flow so the power gain is minimized.

2) Stock tune won't take full advantage of it.

3) CEL will be thrown eventually.

On #1, I also heard that BMW turbo engine DME is load based and will not discount the power gain out of a freer flow exhaust. Not sure.

On #2, what does that mean exactly? More specific on the untaken advantages?
I am not pursuing a new high at down low or something, but instead wanting to address the significant TQ tapering down all the way to fuel cutoff, which is seen on many m2 dyno charts due to stock turbo flow limitation.
Specifically, is catted DP's PRESSURE HOLDING capability at upper range compromised with stock tune? To make no mistake, to hold the pressure, I am not asking turbo to work harder.

On #3, to be reasonable, I will accept the cat failure if it's endured heavy usage for years - stock cat can fail under excessive usage too. I'll just buy a new one.

Appreciate someone in the know shed some lights, especially on #1 and #2.
SeanWRT, what was the outcome with respect to the downpipe. Did you end up with one on stock tune? Which brand did you get and what are your impressions? I'm about to pull the trigger myself.

Thanks in advance.
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      05-12-2017, 10:25 PM   #6
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Quote:
Originally Posted by Deutsches Blut View Post
Quote:
Originally Posted by SeanWRT View Post
I am looking to fit a catted downpipe to my m2 and stay with stock tune. At least that's what I figure works best for me.

I take it many recommend against that approach, the primary 3 reasons being:

1) DME will adjust to the freer flow so the power gain is minimized.

2) Stock tune won't take full advantage of it.

3) CEL will be thrown eventually.

On #1, I also heard that BMW turbo engine DME is load based and will not discount the power gain out of a freer flow exhaust. Not sure.

On #2, what does that mean exactly? More specific on the untaken advantages?
I am not pursuing a new high at down low or something, but instead wanting to address the significant TQ tapering down all the way to fuel cutoff, which is seen on many m2 dyno charts due to stock turbo flow limitation.
Specifically, is catted DP's PRESSURE HOLDING capability at upper range compromised with stock tune? To make no mistake, to hold the pressure, I am not asking turbo to work harder.

On #3, to be reasonable, I will accept the cat failure if it's endured heavy usage for years - stock cat can fail under excessive usage too. I'll just buy a new one.

Appreciate someone in the know shed some lights, especially on #1 and #2.
SeanWRT, what was the outcome with respect to the downpipe. Did you end up with one on stock tune? Which brand did you get and what are your impressions? I'm about to pull the trigger myself.

Thanks in advance.
I used HJS 300 cell downpipe and it worked very well on stock tune. Noticeable improvement on sound and turbo spool up and really no downsides at all.

As I hungered for more power, I went FBO eventually, and on aftermarket tune.
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      05-13-2017, 05:13 AM   #7
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Quote:
Originally Posted by SeanWRT View Post
Quote:
Originally Posted by Deutsches Blut View Post
Quote:
Originally Posted by SeanWRT View Post
I am looking to fit a catted downpipe to my m2 and stay with stock tune. At least that's what I figure works best for me.

I take it many recommend against that approach, the primary 3 reasons being:

1) DME will adjust to the freer flow so the power gain is minimized.

2) Stock tune won't take full advantage of it.

3) CEL will be thrown eventually.

On #1, I also heard that BMW turbo engine DME is load based and will not discount the power gain out of a freer flow exhaust. Not sure.

On #2, what does that mean exactly? More specific on the untaken advantages?
I am not pursuing a new high at down low or something, but instead wanting to address the significant TQ tapering down all the way to fuel cutoff, which is seen on many m2 dyno charts due to stock turbo flow limitation.
Specifically, is catted DP's PRESSURE HOLDING capability at upper range compromised with stock tune? To make no mistake, to hold the pressure, I am not asking turbo to work harder.

On #3, to be reasonable, I will accept the cat failure if it's endured heavy usage for years - stock cat can fail under excessive usage too. I'll just buy a new one.

Appreciate someone in the know shed some lights, especially on #1 and #2.
SeanWRT, what was the outcome with respect to the downpipe. Did you end up with one on stock tune? Which brand did you get and what are your impressions? I'm about to pull the trigger myself.

Thanks in advance.
I used HJS 300 cell downpipe and it worked very well on stock tune. Noticeable improvement on sound and turbo spool up and really no downsides at all.

As I hungered for more power, I went FBO eventually, and on aftermarket tune.
Thanks Sean. I just noticed, based on your profile you reside in Shanghai. I am going to Shanghai next week on business. I travel to Beijing and various other cities 2/3 times annually, but first time in Shanghai; excited to see that city.

Sorry back to business, I'm pretty sure at this point I will go with the fabspeed sport dp. I have to decide regarding tune as I'm considering a Dinan stage 4 down the road and don't want to buy a temporary tune in the meantime. Too many fun decisions.
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