[3LiterBeater]

Originally Posted by ///M TOWN

Running a straight pipe is not something I'd personally do on a stock tune, because the car can run super lean without a Cat

There are some people who are running a straight pipe on a stock ECU… I think that's a bit risky IMO

It's amazing how well my M2 runs currently
I cannot wait to install my new Euro 6 Cat

I was originally worried about this too but was told time and time again that the primary o2 is what's controlling AFR, not the secondary.

That said, some say long term fuel trims can be impacted but there is very little to no data that supports that, from what I've found.

[AmuroRay]

Originally Posted by 3LiterBeater

I was originally worried about this too but was told time and time again that the primary o2 is what's controlling AFR, not the secondary.

That said, some say long term fuel trims can be impacted but there is very little to no data that supports that, from what I've found.

Correct

[F87source]

It's not afr's im worried about - since bmw's have incredibly smart ecus that can adapt. I am more worried about slight overboosting, because with a catless downpipe it spools much faster causing overboosting if not tuned for.

[shaneguags]

Originally Posted by 3LiterBeater

I was originally worried about this too but was told time and time again that the primary o2 is what's controlling AFR, not the secondary.

That said, some say long term fuel trims can be impacted but there is very little to no data that supports that, from what I've found.

my turner and shop just recently data logged my car and we noticed the fuel trims were different with the the valves opened / closed. the car under full boost ran rich when closed and when opened it ran lean. I would like to think a catless down pipe would effect the fuel trims as well with an increase in airflow.

[bentom2]

Originally Posted by ///M TOWN

I bought all new hardware, but thanks for looking out for me

I'm using a lift this Friday simply because my garage is a single and it's tight and I only have two Jack-stands and I'm sure you know the the limitations with only two vs four

I am excited to get it installed

Lift is definitely the way to go then. I don’t think you’d have a very good time on two jack stands.

Good deal on hardware. Didn’t see it mentioned.

[AmuroRay]

Originally Posted by shaneguags

my turner and shop just recently data logged my car and we noticed the fuel trims were different with the the valves opened / closed. the car under full boost ran rich when closed and when opened it ran lean. I would like to think a catless down pipe would effect the fuel trims as well with an increase in airflow.

Well yeah, closing the exhaust valves is going to add back pressure to the system.

[3LiterBeater]

Originally Posted by F87source

It's not afr's im worried about - since bmw's have incredibly smart ecus that can adapt. I am more worried about slight overboosting, because with a catless downpipe it spools much faster causing overboosting if not tuned for.

While I haven't done any deep diving into this data, I've put about 10hrs of track time on the car without any code other than the catalyst.

When you say overboost, are you speaking on the car throwing a code/ hitting a limp mode or just small increments of boost outside of what the car is targeting?

I can confirm my boost levels "appear" consistent but obviously that changes dramatically based on temps and various other factors. Ranges are all the way from 13.5-17psi per weekend

[///M TOWN]

Originally Posted by 3LiterBeater

While I haven't done any deep diving into this data, I've put about 10hrs of track time on the car without any code other than the catalyst.

When you say overboost, are you speaking on the car throwing a code/ hitting a limp mode or just small increments of boost outside of what the car is targeting?

I can confirm my boost levels "appear" consistent but obviously that changes dramatically based on temps and various other factors. Ranges are all the way from 13.5-17psi per weekend

What mods are you running in total ⁉️

[F87source]

Originally Posted by 3LiterBeater

While I haven't done any deep diving into this data, I've put about 10hrs of track time on the car without any code other than the catalyst.

When you say overboost, are you speaking on the car throwing a code/ hitting a limp mode or just small increments of boost outside of what the car is targeting?

I can confirm my boost levels "appear" consistent but obviously that changes dramatically based on temps and various other factors. Ranges are all the way from 13.5-17psi per weekend

Generally you'd see the actual boost deviate higher than the targets during spool up, it shouldn't be anything too crazy that you'd limp mode on. But it's not ideal.

[///393]

Originally Posted by F87source

Generally you'd see the actual boost deviate higher than the targets during spool up, it shouldn't be anything too crazy that you'd limp mode on. But it's not ideal.

Are you implying the ECU is not able to compensate for said minor deviation in boost pressures? You say you’re not worried about AFR but what else would be the concern of an additional .5psi be if not AFR?

Aren’t these cars basically MAF with MAP to supplement? These concerns seem slightly OCD to me given BMW offered an optional exhaust that would present similar “concerns”.

I know you’re well versed on all this theory and what not F87source but I’d love for a tuner with extensive experience tuning BM3 or Ecutek to weigh in on just how material concerns like this are because I’m missing something.

[F87source]

Originally Posted by wilson kop

Are you implying the ECU is not able to compensate for said minor deviation in boost pressures? You say you’re not worried about AFR but what else would be the concern of an additional .5psi be if not AFR?

Aren’t these cars basically MAF with MAP to supplement? These concerns seem slightly OCD to me given BMW offered an optional exhaust that would present similar “concerns”.

I know you’re well versed on all this theory and what not F87source but I’d love for a tuner with extensive experience tuning BM3 or Ecutek to weigh in on just how material concerns like this are because I’m missing something.

The ECU will compensate for it when it passes the target boost pressure, but the fact that it'll over boost will still occur until tuned for.

AFR's should be fine as the car will adapt to it (as long as you aren't asking for it to adjust stft more than +/-30% which is the max) the over boost if small should also be ok - only if it isn't a major issue. 0.5 psi is very little and should be ok, but what happens if the over boost is alot, say a couple of psi when you're doing a full throttle pull? This scenario could cause a large knock event, because the ECU isn't expecting this. In higher gears the turbo spools faster than the rpms increase, and if you over boost alot here this could exacerbate lspi, and lspi is what blows motors.

Imo I'm not ok with any of this on my personal car, I would never run a single mod that is not closed loop (i.e. charge pipes and intercooler which don't affect anything as they cannot alter the volume of air going into or out of the engine, or affect afrs) without a tune. So this thread kind of bothers me, because you ideally should never run a single non "closed loop" mod without a tune, you should also never rely on the ECU to adapt for everything or else you're asking for trouble (especially if you're asking for too much or somehow end up running in open loop mode). I always say bmw owners are really spoiled (myself included because I used to spend $1k on dyno tunes for every single mod I installed on my sti) because of how strong these engines are and how smart these ecus are, and how these things allow bmw owners to get away with things that shouldn't be permitted. But this teaches really bad habits, like chasing power mods over doing supporting mods first. Anyways this was just my rambling - ignore if you wish it's just my opinion coming from japanese cars which were really fastidious.


No, these cars are map based, the maf sensor does very little (idle conditions), as soon as your on load it's map based.


A cat back exhaust does little to affect anything, the catalytic converter is what your should be worried about. Even on a Subaru where the ecus are extremely stupid and you must tune for literally every mods even an intake, catbacks don't need a tune.



Mhd was the one that told me not to flash stage 0 in order to delete the cel and run a catless downpipe. They told me it would be best to run it with a tune so I wouldn't get overboosting issues.

[///393]

Thanks for your reply. Always appreciate your posts.

[3LiterBeater]

Originally Posted by ///M TOWN

What mods are you running in total ⁉️

Only a catless DP, drop in filter and intercooler

[///M TOWN]

Originally Posted by 3LiterBeater

Only a catless DP, drop in filter and intercooler

Hopefully installing my new cat tomorrow

What straight pipe are you running?

You changed your CP, yes?

[3LiterBeater]

Originally Posted by ///M TOWN

Hopefully installing my new cat tomorrow

What straight pipe are you running?

You changed your CP, yes?

Standard MPE, I did do the charge pipe with the intercooler.

Amazed that this part still exists in plastic, lol

[3LiterBeater]

Originally Posted by F87source

The ECU will compensate for it when it passes the target boost pressure, but the fact that it'll over boost will still occur until tuned for.

AFR's should be fine as the car will adapt to it (as long as you aren't asking for it to adjust stft more than +/-30% which is the max) the over boost if small should also be ok - only if it isn't a major issue. 0.5 psi is very little and should be ok, but what happens if the over boost is alot, say a couple of psi when you're doing a full throttle pull? This scenario could cause a large knock event, because the ECU isn't expecting this. In higher gears the turbo spools faster than the rpms increase, and if you over boost alot here this could exacerbate lspi, and lspi is what blows motors.

Imo I'm not ok with any of this on my personal car, I would never run a single mod that is not closed loop (i.e. charge pipes and intercooler which don't affect anything as they cannot alter the volume of air going into or out of the engine, or affect afrs) without a tune. So this thread kind of bothers me, because you ideally should never run a single non "closed loop" mod without a tune, you should also never rely on the ECU to adapt for everything or else you're asking for trouble (especially if you're asking for too much or somehow end up running in open loop mode). I always say bmw owners are really spoiled (myself included because I used to spend $1k on dyno tunes for every single mod I installed on my sti) because of how strong these engines are and how smart these ecus are, and how these things allow bmw owners to get away with things that shouldn't be permitted. But this teaches really bad habits, like chasing power mods over doing supporting mods first. Anyways this was just my rambling - ignore if you wish it's just my opinion coming from japanese cars which were really fastidious.


No, these cars are map based, the maf sensor does very little (idle conditions), as soon as your on load it's map based.


A cat back exhaust does little to affect anything, the catalytic converter is what your should be worried about. Even on a Subaru where the ecus are extremely stupid and you must tune for literally every mods even an intake, catbacks don't need a tune.



Mhd was the one that told me not to flash stage 0 in order to delete the cel and run a catless downpipe. They told me it would be best to run it with a tune so I wouldn't get overboosting issues.

You're right on this, on both ends of the spectrum.

We learned the hard way on my buddy's WRX back in the day. Even a cone filter caused it to hit a hard cutoff at 4k RPM.

[3LiterBeater]

Originally Posted by shaneguags

my turner and shop just recently data logged my car and we noticed the fuel trims were different with the the valves opened / closed. the car under full boost ran rich when closed and when opened it ran lean. I would like to think a catless down pipe would effect the fuel trims as well with an increase in airflow.

I'd think the car would see this and adapt accordingly, based on what I've read/ seen from others

[///M TOWN]

Originally Posted by 3LiterBeater

Standard MPE, I did do the charge pipe with the intercooler.

Amazed that this part still exists in plastic, lol

The 2018 CP is the factory improvement

But yeah with it being plastic I sold mine for $100 and replaced it as a Maintenance Preventive measure

[///M TOWN]

Just installed my new Euro 6 Cat

90 day part from Germany 🇩🇪

[F87source]

Originally Posted by 3LiterBeater

You're right on this, on both ends of the spectrum.

We learned the hard way on my buddy's WRX back in the day. Even a cone filter caused it to hit a hard cutoff at 4k RPM.

Yeah I was heavy into the Subaru world before going to bmw, and all I can say is the Subaru ecus are straight up stupid. This is probably why sti's always blew motors because they are unable to adapt and fully prevent feedback knock even on the stock tune (I.e. when. Heat soaked it never pulls enough timing to prevent knock when starting from a red light). This is why you'd always have to tune them with huge head room and safety margins.

Even a car back exhaust slightly altered fuel trims, but thankfully not enough to require a tune.

Originally Posted by ///M TOWN

Just installed my new Euro 6 Cat

90 day part from Germany 🇩🇪

Nice!!! What a beauty! Get us some exhaust clips if you can!

[///M TOWN]

Originally Posted by F87source

Yeah I was heavy into the Subaru world before going to bmw, and all I can say is the Subaru ecus are straight up stupid. This is probably why sti's always blew motors because they are unable to adapt and fully prevent feedback knock even on the stock tune (I.e. when. Heat soaked it never pulls enough timing to prevent knock when starting from a red light). This is why you'd always have to tune them with huge head room and safety margins.

Even a car back exhaust slightly altered fuel trims, but thankfully not enough to require a tune.

Nice!!! What a beauty! Get us some exhaust clips if you can!

It's sounds sooo good

I will soon