[TurboRed]

Hey everyone!
I’d like to get your advice on modifying my 2021 X5M Competition.

The goal of the modifications is to increase power without introducing significant risks to the engine (or other components) and to slightly improve the sound.

I’m planning to unlock the ECUs through Femto (I’ll send both ECUs to Finland) and use Bootmod3 (I’ve been using Bootmod3 successfully on my M2 Comp F87 and I’m very happy with it). After that, I’m considering two possible paths and haven’t yet decided which would be optimal, especially since I plan to keep this car for a long time and want to avoid modifications that could significantly reduce its lifespan.

Options:
1) Flash Stage 1 and leave it as is.
2) Replace the stock downpipes with sport ones featuring 200-300 cell cats and run either Stage 1 or Stage 2 (depending on which I like more).


I have a few questions:

1) If I install downpipes with 200-300 cell cats and keep the rest of the exhaust system stock:

1.1) Will it be too loud?

The car is used as a daily family vehicle and for long trips, plus it’s driven in Europe, so an overly loud exhaust wouldn’t be appropriate. I’m mostly satisfied with the stock sound in Sport+ mode with the enhanced exhaust sound button activated. However, if the sound could be slightly angrier and livelier, and if I could add a bit of burbles (thankfully, these can be finely tuned with Bootmod3), that would be great.

I’m worried it might become too loud, and I’ll have to replace the downpipes back. I recently went through a similar situation with my M2, where I’m currently switching from catless downpipes to 200-cell downpipes because the catless setup became unbearably loud (both with the stock exhaust and later with Valvetronic). It also introduced drone, rattles, and annoying resonances at certain RPMs.

1.2) Will the additional OPF/GPF filters in the mid-pipes melt?

My tuning parts supplier warned that with higher boost and the absence of OPF/GPF in the downpipes (replaced by high-flow cats), the filters in the mid-pipes could melt. They suggested replacing the mid-pipes with performance ones that don’t have OPF/GPF. However, if that’s the case, I understand the sound would likely become excessively loud, which would rule out this option.

2) How noticeable is the power increase, and how much does the sound improve on Stage 1?

How safe would it be to enable light burbles with stock downpipes?

ProTuningFreaks (the company behind Bootmod3) claims the following power gains:
• Stage 1 91 octane: up to 11% HP / 18% TQ
• Stage 1 93 octane: up to 13% HP / 19% TQ
• Stage 1 E30 octane: up to 19% HP / 26% TQ
• Stage 2 91 octane: up to 15% HP / 22% TQ
• Stage 2 93 octane: up to 18% HP / 24% TQ
• Stage 2 E30 octane: up to 24% HP / 34% TQ

Any thoughts and opinions are welcome! 😊

[weinerbarn]

I just modded my 2020 X5MC. First of all, the OTS maps from Bootmod3 for the F90/F95 are garbage. The software itself is great as a "delivery system" for the tunes but you need to get a custom tune done so budget in another $800-1K for that. Forget about of the primary downpipes. They aren't necessary and they'll be too loud and stink. Get the secondary cat delete pipes and that will free up some flow and add just enough sound with stock competition exhaust. You can always add the mid/x-pipe if you want more sound but the secondary cat delete adds just enough bark to it on upshifts. You'll also want a trans tune with engine tune to maximize the performance.

Here's my current setup:

- Bootmod3 for tune loading (Was not happy with Stage 1 OTS. Lots of drivability and drivetrain errors)
- HC Performance Tune. Includes 2 maps (93 and E40). https://hc-performance.com/products/...umpgas-e40-map
- XHP Tune (Stage 3)
- Ethanol Sensor to run E40. (I just worked with them this week to make a custom kit for F95/F96 and did an install video) https://fuel-it.com/collections/f-chassis. Kit not released yet for the F95 but if you call, they should know what you need since they just made the right hose and fittings for me.
- Secondary Cat delete. https://www.evolutionracewerks.com/node/381

OR .... you can save yourself a ton of money and just get the secondary cat delete and add a JB4. You'll get 80% of the performance and none of the other hassle. My 2020 X5MC was doing Dragy verified 3.0s 0-60 with the JB4 on 93 pump gas. Those 2 mods will cost less than the Femto unlock alone.

[X5MnM3comp]

Originally Posted by weinerbarn

I just modded my 2020 X5MC. First of all, the OTS maps from Bootmod3 for the F90/F95 are garbage. The software itself is great as a "delivery system" for the tunes but you need to get a custom tune done so budget in another $800-1K for that. Forget about of the primary downpipes. They aren't necessary and they'll be too loud and stink. Get the secondary cat delete pipes and that will free up some flow and add just enough sound with stock competition exhaust. You can always add the mid/x-pipe if you want more sound but the secondary cat delete adds just enough bark to it on upshifts. You'll also want a trans tune with engine tune to maximize the performance.

Here's my current setup:

- Bootmod3 for tune loading (Was not happy with Stage 1 OTS. Lots of drivability and drivetrain errors)
- HC Performance Tune. Includes 2 maps (93 and E40). https://hc-performance.com/products/f9x-s63t4-hcp-pumpgas-e40-map
- XHP Tune (Stage 3)
- Ethanol Sensor to run E40. (I just worked with them this week to make a custom kit for F95/F96 and did an install video) https://fuel-it.com/collections/f-chassis. Kit not released yet for the F95 but if you call, they should know what you need since they just made the right hose and fittings for me.
- Secondary Cat delete. https://www.evolutionracewerks.com/node/381

OR .... you can save yourself a ton of money and just get the secondary cat delete and add a JB4. You'll get 80% of the performance and none of the other hassle. My 2020 X5MC was doing Dragy verified 3.0s 0-60 with the JB4 on 93 pump gas. Those 2 [...]

Hey what’s your settings for xhp stage 3? Are you running on just the ots map as is or did you modify any settings? I just flashed xhp stage 3 ots as is, not familiar enough to play with the additional settings yet. Running the tune with racechip gts. Prior to the xhp flash I also had the rc xlr throttle booster ran in conjunction with the gts. I thought the xhp tune and xlr would fight against each other so I currently have the xlr turned off. Out of my expectation, I actually like the xlr better than the xhp tune. I wonder if the additional settings I haven’t touched would help dial in to optimize the performance. But as of now, I’m not blown away with the tune even on stage 3.

[Brandt51]

I got the downpipes, but it’s American so no OPF. I haven’t had any smell issues either, but it’s cold start is def loud! But it tames down and with the exhaust valve closed; no major pops and burbles and it’s alright. But because of the tune, it can sound real aggressive if you’d like it to.

Mine is stock except for downpipes and a custom tune.

Good luck, curious to hear how it goes!

[TurboRed]

Originally Posted by weinerbarn

I just modded my 2020 X5MC. First of all, the OTS maps from Bootmod3 for the F90/F95 are garbage. The software itself is great as a "delivery system" for the tunes but you need to get a custom tune done so budget in another $800-1K for that. Forget about of the primary downpipes. They aren't necessary and they'll be too loud and stink. Get the secondary cat delete pipes and that will free up some flow and add just enough sound with stock competition exhaust. You can always add the mid/x-pipe if you want more sound but the secondary cat delete adds just enough bark to it on upshifts. You'll also want a trans tune with engine tune to maximize the performance.

Here's my current setup:

- Bootmod3 for tune loading (Was not happy with Stage 1 OTS. Lots of drivability and drivetrain errors)
- HC Performance Tune. Includes 2 maps (93 and E40). https://hc-performance.com/products/...umpgas-e40-map
- XHP Tune (Stage 3)
- Ethanol Sensor to run E40. (I just worked with them this week to make a custom kit for F95/F96 and did an install video) https://fuel-it.com/collections/f-chassis. Kit not released yet for the F95 but if you call, they should know what you need since they just made the right hose and fittings for me.
- Secondary Cat delete. https://www.evolutionracewerks.com/node/381

OR .... you can save yourself a ton of money and just get the secondary cat delete and add a JB4. You'll get 80% of the performance and none of the other hassle. My 2020 X5MC was doing Dragy verified 3.0s 0-60 with the JB4 on 93 pump gas. Those 2 mods will cost less than the Femto unlock alone.

Weinerbarn, thank you so much for sharing your experience in such detail!
This has been incredibly helpful and clarified a lot for me!
I’ve already sent a request to HCP.

A few questions:
1. Am I correct in understanding that, despite HCP’s recommendation to install high-flow downpipes on the page describing this map (https://hc-performance.com/products/...umpgas-e40-map), I can instead install only secondary cat delete pipes?
2. Are you using high-flow drop-in air filters, as recommended by HCP?
3. Regarding xHP:
3.1) Did you purchase the xHP TCU Custom Map Service (https://www.xautomotive.com/products/custom-map-service) or the xHP TCU Flash Combo (https://www.xautomotive.com/products...740852654304)?
4. Did you also purchase xDelete (https://www.xautomotive.com/products/xdelete)?
5. I travel a lot in this X5M, and RON98 isn’t always available in every country I visit. Is there any way to retain the ability to switch to a map that allows RON95 (for example, the standard factory map)?

[TurboRed]

Originally Posted by Brandt51

I got the downpipes, but it’s American so no OPF. I haven’t had any smell issues either, but it’s cold start is def loud! But it tames down and with the exhaust valve closed; no major pops and burbles and it’s alright. But because of the tune, it can sound real aggressive if you’d like it to.

Mine is stock except for downpipes and a custom tune.

Good luck, curious to hear how it goes!

Hmm… interesting, why don’t you have any issues with the smell... My M2 Competition F87 started smelling awful after installing catless downpipes, which (in addition to the excessive noise) led me to replace the catless downpipes with 200-cell catted ones (I’m actually taking it to the shop for this in the next few days).

Which tune are you using exactly? BM3, XHP, or something else? And what are your impressions of this tune?

[weinerbarn]

Originally Posted by TurboRed

Weinerbarn, thank you so much for sharing your experience in such detail!
This has been incredibly helpful and clarified a lot for me!
I’ve already sent a request to HCP.

A few questions:
1. Am I correct in understanding that, despite HCP’s recommendation to install high-flow downpipes on the page describing this map (https://hc-performance.com/products/...umpgas-e40-map), I can instead install only secondary cat delete pipes?
2. Are you using high-flow drop-in air filters, as recommended by HCP?
3. Regarding xHP:
3.1) Did you purchase the xHP TCU Custom Map Service (https://www.xautomotive.com/products/custom-map-service) or the xHP TCU Flash Combo (https://www.xautomotive.com/products...740852654304)?
4. Did you also purchase xDelete (https://www.xautomotive.com/products/xdelete)?
5. I travel a lot in this X5M, and RON98 isn’t always available in every country I visit. Is there any way to retain the ability to switch to a map that allows RON95 (for example, the standard factory map)?

1. Yes. It may just have slightly less top end power. I confirmed this with HCP.
2. No. I may when they need changing. I'm only at 6K miles currently. The factory system is not a known restriction anyway.
3. Just the flash combo w/ WiFi adapter. You have to use a supported adapter so easiest just to get the kit. https://www.xautomotive.com/products...50423124033865
4. No xDelete. This thing needs all the traction it can get.
5. Yeah. Bootmod comes with 1 OTS tune (you pick a stage and octane level) and also backs up your factory tune. So if you buy Bootmod3 and HCP, you could have something like this as an example ...

- HCP Stage 2 93
- HCP Stage 2 E40
- BM3 Stage 1 91 or ACN 91 (more than stock but for less quality fuels)
- Factory Map level or F95 Competition (Stage 0+)

You can switch the maps very easily, even at a gas station. It takes 30 seconds to switch "within a vendor map" such as between HCP maps as it's a small config change. If you switch to/from factory or BM3 OTS, the flash time is maybe a couple mins as it has to completely flash both DME's.

[Brandt51]

Originally Posted by TurboRed

Hmm… interesting, why don’t you have any issues with the smell... My M2 Competition F87 started smelling awful after installing catless downpipes, which (in addition to the excessive noise) led me to replace the catless downpipes with 200-cell catted ones (I’m actually taking it to the shop for this in the next few days).

Which tune are you using exactly? BM3, XHP, or something else? And what are your impressions of this tune?

I have down pipes in the M2 as well and that doesn’t smell either. I mean, I can smell the lack of MPGs haha.

Tunes are custom. A race shop did the work, I just wrote the checks and drive em. It’s cool there are several ways to get the same results with Bimmers though. Lots of options out there.

[weinerbarn]

Originally Posted by X5MnM3comp

Hey what’s your settings for xhp stage 3? Are you running on just the ots map as is or did you modify any settings? I just flashed xhp stage 3 ots as is, not familiar enough to play with the additional settings yet. Running the tune with racechip gts. Prior to the xhp flash I also had the rc xlr throttle booster ran in conjunction with the gts. I thought the xhp tune and xlr would fight against each other so I currently have the xlr turned off. Out of my expectation, I actually like the xlr better than the xhp tune. I wonder if the additional settings I haven’t touched would help dial in to optimize the performance. But as of now, I’m not blown away with the tune even on stage 3.

I'm running unmodified Stage 3 OTS for XHP. The primary reason I am running this is to allow full power of the tune. I ran into issues with Bootmod3. The transmission will tell the engine controller (DME) to pull power if it exceeds certain thresholds of torque requested. BM3 has a setting for "TCU Torque Limit Patch" to override this in the OTS tune settings but it was throwing crazy drivetrain errors if I tried to launch the car below 20 MPH so I disabled it and went with HCP and XHP. BM3 support was unhelpful when I reached out to them about the errors and were seemingly clueless that setting even existed which is why I made my previous comments about the OTS tunes. I wish they'd sell the software w/o OTS tunes so we can apply the potential $300 savings toward a custom tune. It's a huge waste to buy BM3 and you know you're not going to use the included tune which is built into their pricing.

Unfortunately it's been really cold here lately so I haven't been able to fully test and log the new setup. It was still a bit wet with melting snow and barely 50 degrees when I did the ethanol sensor. Now it's back into the teens on temps so I'm not going to abuse it or take a chance on damaging my summer tires. I may do a dedicated thread on my experience when the weather gets better and I can thoroughly test. For now, I'm just hooning my F350 diesel around

[X5MnM3comp]

Originally Posted by weinerbarn

I'm running unmodified Stage 3 OTS for XHP. The primary reason I am running this is to allow full power of the tune. I ran into issues with Bootmod3. The transmission will tell the engine controller (DME) to pull power if it exceeds certain thresholds of torque requested. BM3 has a setting for "TCU Torque Limit Patch" to override this in the OTS tune settings but it was throwing crazy drivetrain errors if I tried to launch the car below 20 MPH so I disabled it and went with HCP and XHP. BM3 support was unhelpful when I reached out to them about the errors and were seemingly clueless that setting even existed which is why I made my previous comments about the OTS tunes. I wish they'd sell the software w/o OTS tunes so we can apply the potential $300 savings toward a custom tune. It's a huge waste to buy BM3 and you know you're not going to use the included tune which is built into their pricing.

Unfortunately it's been really cold here lately so I haven't been able to fully test and log the new setup. It was still a bit wet with melting snow and barely 50 degrees when I did the ethanol sensor. Now it's back into the teens on temps so I'm not going to abuse it or take a chance on damaging my summer tires. I may do a dedicated thread on my experience when the weather gets better and I can thoroughly test. For now, I'm just hooning my F350 diesel around

I see. I didn’t know you also had a bm3 tune on it. Also surprised to hear this counterintuitive feature built into their ots map for the f95. What stage of ots map of bm3 are you on? I have a new g80 as well, only did the piggies and Bolt ons similar to what I have on the f95 except the xhp flash because there’s a csl flash for the transmission i got on the g80. on that forum, people who have their dme unlocked and got the bm3 say that xhp really brings the overall performance to another level because they say the bm3 engine tune doesn’t alter the transmission logics. I would get bm3 out of all tunes only if dmes are not locked. But I can stand the fact to go through the complicated process even though I have 2 cars to spare the downtimes.

Prior to flashing the xhp, i didn’t like the excessive power/ torque drag till redline on low gears when I put the car on d3. it’s way too aggressive for local drivers given my exhaust setup too. Also feels like damaging the tranny. For that reason I set my m1 and m2 both on d2. After the xhp flash, the issue still exists plus I lost some torque on the low gears which helped me eliminate turbo lag from a stop. Perhaps it’s just the throttle booster I used to turned on that I disabled now. Anyhow I’m hoping to get more familiarize with the xhp so I can start utilizing the features to try and dial in what I like. Thanks for your insight. It’s good to see another f95 owner here with the xhp flash to share experience.

[Brandt51]

Originally Posted by TurboRed

Which tune are you using exactly? BM3, XHP, or something else? And what are your impressions of this tune?

Sorry, forgot to address this. A race shop named AR Motorsports in Beaverton OR did the tuning with whoever it is they use. They’re legit and are into racing. The S63 was locked and they (fucking 2?!?) had to go to Finland as well. I once knew, but forgot the outfits. Same one everybody uses. Both tunes for the S55 and S63 tho are of the type where they won’t break stuff like hard parts. The M2 dynos 505. Never dyno’d the X5 as of yet. But like mentioned earlier, it easily blasts thru safeties and throws chassis faults unless all the TC stuff is turned all the way off. Not the M2 though. But it’s also manual and im usually concerned about going around, so I’m pretty pussy behind the wheel.

MPGs are not good. At all. If I had to do it all over again, I prob would now, but I have more than one car. If not, the X5M is prenty dang fast stock. But sounds like it’s held back. Haha.

Good luck all. Good MPGs never got anybody laid. Let’s rock!

[weinerbarn]

X5MnM3comp I’m just using Bootmod3 (BM3) to load the tune now. It’s more like an app. I had been using their Stage 1 93 OTS map but when it ran like crap, I bought HCP and XHP which is considered a prerequisite for HCP tune. HCP publishes the tune in my BM3 map list. You still have to use the BM3 app to load it and can also apply some mild mods as well like burble settings.

[weinerbarn]

FYI … Fuel-IT released the ethanol sensor kit for the F95. It’s listed under the dropdown on this page https://fuel-it.com/products/fuel-it...s63tu-m5-m6-m8

Highly recommend this kit if your considering an E40 or similar tune. The quality of the entire kit is top notch.

[Brandt51]

Originally Posted by weinerbarn

FYI … Fuel-IT released the ethanol sensor kit for the F95. It’s listed under the dropdown on this page https://fuel-it.com/products/fuel-it-bluetooth-flex-fuel-kit-s63tu-m5-m6-m8

Highly recommend this kit if your considering an E40 or similar tune. The quality of the entire kit is top notch.

E40 def has his own distinct West Coast style…oh wait.

Jk, but a sensor is needed to run the corn ethanol based tunes to use with E85?

[DoubleG]

I don't think the ethanol content sensor is actually needed to run most ethanol based tunes as many do not read the sensor data to adjust the tune. I believe the sensor and app are typically just information for the driver to view and confirm the ethanol content percentage currently in the fuel tank. Kind of a piece of mind thing.

However there may be some E tunes that can read the sensors output and adjust boost and timing for different ethanol content mixtures.

For example, I have a flex fuel tune in my modified TrackHawk that self adjusts ignition timing based on different ethanol content percentages. No ethanol sensor required.

But for piece of mind, I also added a Zeitronix ECA ethanol content sensor and a gauge just to know exactly what the ethanol content is in my fuel tank. My flex fuel tune does not use the data from the ethanol sensor in anyway to adjust the tune from 93 octane to an E90 blend or anything in-between.

[weinerbarn]

Originally Posted by Brandt51

E40 def has his own distinct West Coast style…oh wait.

Jk, but a sensor is needed to run the corn ethanol based tunes to use with E85?

Not required but definitely easier and recommended. The ethanol sensor just tells you what the current actual percentage is. You can certainly do the mad scientist thing and buy a manual ethanol sensor to test the E85 you source and then blend from there. The most important part is that you know what you end up with so you have enough octane for the tune versus hope and prayer. You cannot assume "E85" is actually 85% ethanol. My latest batch I got locally was 71% which meant I had to add considerably more to hit the E40 number I needed based on my tune. I just look in my app now since the ethanol sensor comes with a bluetooth adapter. After I added the 11 gallons of E71 to a half tank of 93 E10, the app showed E38. I will add another gallon after driving and burning off some fuel.

If you run a JB4 piggyback, the Fuel-IT sensor I bought comes with a wire to connect to the JB4. This allows the JB4 to auto adjust the map to the actual fuel which is pretty cool.

[Brandt51]

Originally Posted by weinerbarn

Not required but definitely easier and recommended. The ethanol sensor just tells you what the current actual percentage is. You can certainly do the mad scientist thing and buy a manual ethanol sensor to test the E85 you source and then blend from there. The most important part is that you know what you end up with so you have enough octane for the tune versus hope and prayer. You cannot assume "E85" is actually 85% ethanol. My latest batch I got locally was 71% which meant I had to add considerably more to hit the E40 number I needed based on my tune. I just look in my app now since the ethanol sensor comes with a bluetooth adapter. After I added the 11 gallons of E71 to a half tank of 93 E10, the app showed E38. I will add another gallon after driving and burning off some fuel.

If you run a JB4 piggyback, the Fuel-IT sensor I bought comes with a wire to connect to the JB4. This allows the JB4 to auto adjust the map to the actual fuel which is pretty cool.

WOW. Yeah, manual mixing sounds like it’s for professionals or track tuning. Sensor sounds a lot easier! I don’t even like mixing oil for two stroke machines!

[JMcLellan]

FWIW, I have had really good luck with running stage 1 and stage 2 tunes with the 91 or 93 octane maps via MHD. My go-to was to always add 2 to 3 gallons of E85 when I filled up to avoid timing corrections, and throttle closures. My thought was to always provide more octane than the OTS map was calling for. I found plenty of power out of this for daily driving and didn't have the need to go full E30 or more where I would want to have a flex fuel sensor.

This was with a previous M240i with the B58 motor so not sure how it compares to this application.

[TurboRed]

Originally Posted by weinerbarn

1. Yes. It may just have slightly less top end power. I confirmed this with HCP.
2. No. I may when they need changing. I'm only at 6K miles currently. The factory system is not a known restriction anyway.
3. Just the flash combo w/ WiFi adapter. You have to use a supported adapter so easiest just to get the kit. https://www.xautomotive.com/products...50423124033865
4. No xDelete. This thing needs all the traction it can get.
5. Yeah. Bootmod comes with 1 OTS tune (you pick a stage and octane level) and also backs up your factory tune. So if you buy Bootmod3 and HCP, you could have something like this as an example ...

- HCP Stage 2 93
- HCP Stage 2 E40
- BM3 Stage 1 91 or ACN 91 (more than stock but for less quality fuels)
- Factory Map level or F95 Competition (Stage 0+)

You can switch the maps very easily, even at a gas station. It takes 30 seconds to switch "within a vendor map" such as between HCP maps as it's a small config change. If you switch to/from factory or BM3 OTS, the flash time is maybe a couple mins as it has to completely flash both DME's.

Thank you so much for the detailed response! It’s truly heartwarming to see people like you who share their time and expertise — it’s incredibly valuable.

You mentioned: “Forget about the primary downpipes. They aren’t necessary and they’ll be too loud and stink.”
Do you think this will still be the case if they are high-flow downpipes with sport cats (e.g., 300 CPSI instead of the 800 CPSI stock ones)?

I feel like this could be the golden middle ground — it would provide better flow and improved sound but might not cause the excessive smell. What’s your take on this?

Do you have any video recordings that would allow me to hear the sound after you installed the secondary cat delete pipes?

P.S. By the way, in one experienced tuning shop that specializes in S63M engines (S63B44T4), they mentioned that keeping downpipes with cats while running Stage 2 or 3 can lead to an issue where the backpressure pulls carbon deposits from the cats into the cylinders during moments of reverse pressure. As a result, scoring can occur on the cylinder walls (since they have Alusil or a similarly delicate coating). What’s your opinion on this?

[weinerbarn]

Originally Posted by TurboRed

Thank you so much for the detailed response! It’s truly heartwarming to see people like you who share their time and expertise — it’s incredibly valuable.

You mentioned: “Forget about the primary downpipes. They aren’t necessary and they’ll be too loud and stink.”
Do you think this will still be the case if they are high-flow downpipes with sport cats (e.g., 300 CPSI instead of the 800 CPSI stock ones)?

I feel like this could be the golden middle ground—it would provide better flow and improved sound but might not cause the excessive smell. What’s your take on this?

P.S. By the way, in one experienced tuning shop that specializes in S63M engines (S63B44T4), they mentioned that keeping downpipes with cats while running Stage 2 or 3 can lead to an issue where the backpressure pulls carbon deposits from the cats into the cylinders during moments of reverse pressure. As a result, scoring can occur on the cylinder walls (since they have Alusil or a similarly delicate coating). What’s your opinion on this?

There are sport cat downpipes that flow pretty much like catless but have no smell and no engine light ... but they are also like $3K since they have GESI or similar cats. Active Autowerke is an example. I've never heard of the carbon issue or the reverse flow. That seems a bit far fetched since it would have to get past the turbos first which are always spinning and have a specific directional spin and blade direction. It would end up engine braking like my diesel does. I'm not an engine builder but like I said ... I asked the tuner who is literally one of the top names in S63 tuning and he told me it would be fine.

In the end it all comes down to how you are going to use it. I'm not building a race car. I just wanted something that was tuned by a trusted and respected tuner and all the power I would likely ever use on the street. I wasn't concerned with losing say 30 HP by leaving the primaries in place. It's also plenty loud with the secondary cat delete and stock competition exhaust for my tastes ... but I'm also an older adult with teenage kids. I'm not interested in taking the wife out for a nice dinner and we show up smelling like I just mowed the lawn.