[undergroundhead]

Originally Posted by Nezil

I can't remember who posted it, so I apologise for not giving credit where it's due, but I'd heard it suggested that the lag between shifts with the 6MT is a software thing, and not true turbo lag.

This bothered me quite a bit, mostly because it went against established thought, including my own thoughts on the subject, but it could explain why this lag between shifts

a) doesn't improve by making engine modifications that in theory should
b) doesn't happen when shifting above 6,000 rpm.

I'd also heard that this phenomenon also happens with the M2C. The S55 is fundamentally very similar to the N55, but the induction system is different enough that I'd expect a different characteristic between shifts.

So I started investigating this a little deeper by looking in to some logs. These logs were captured with 100% accelerator pedal input, shifting from second to third but before 6,000 rpm.

I'm no expert at reading logs, but it appears that the Waste gate Duty Cycle trace shows the waste gate opening after I've got back on the gas, for a period of 1 second. This prevents boost from building until it again goes to 100% duty cycle and boost again climbs.



I have some questions then about this finding:

• Can anyone comment on if I'm reading this log data correctly?
• Can anyone comment on if the 6MT S55 M2C also has this behaviour?
• Can anyone comment on if the DCT OG MG (or M2C) has this behaviour if you shift manually below 6K rpm whilst flooring it?
• If this is a software defined / controlled behaviour, can it be fixed or improved in a tune?

First, let me say thank you for this post and all the extensive data you have collected on this issue. Impressive, and well explained/thought out.

Just bought a brand new M2C 6MT, and I am at 900 miles (still in break in period). This issue is DRIVING ME NUTS. I see a lot of very constructive back and forth here analyzing the results of these data logs, and as a lover of all things math related, I am totally nerding out on these data log plots. But to be honest, none of this is needed to understand what the OP is feeling: simply jump into the driver's seat of a M2C (or regular M2 apparently) with a manual transmission and give it a rip through the gears. To anyone that is a gear head and enjoys a spirited drive with a manual transmission and has any experience at all with other vehicles, it will be IMMEDIATELY apparent that something is "electronically" holding this car back in a major way when standing on the throttle after an upshift. No question about it. It is that bad and obvious guys.

Again, I am still in the break in period so everything I describe is from the reference frame of a car being shifted under 5500 RPM.

Let me try and paint a picture of what this feels like and how annoying it is, and I am not being hyperbolic here. Pick a gear, give it full throttle, choose a shift point, and execute a quick upshift to the next gear and immediately fully depress the throttle when the clutch is released. For full 0.5-1.0 seconds, NOTHING happens to accelerate this car. No data logs here, but the butt dyno says this car isn't even putting out 100 horsepower during the duration of this short period. Then, like a switch is flipped, power instantly comes back on strong and whatever boost you lost starts to quickly build back up. This effect happens every time, for the same duration, regardless of drive mode settings, regardless of whatever boost pressure you were at before shift, regardless of engine RPM, regardless of the speed of your shift. And it happens distinctly before any turbo lag effects kick in (which is minimal in my opinion). It makes you feel at first like you suck at driving a manual or something, its abrupt and not smooth, readily apparent to the driver or passenger alike. It feels like if you decided to drag race a car with 100 less HP and a driver with exactly equal shift speeds, you would lose solely because of this delay every shift. Most simply put, you slam the accelerator and the M2 says "NOPE......OK now go".

Before ever reading this post or any others related, my immediate impression was that the car was cutting off fuel flow for this short duration for some reason, the power drop is that pronounced. Ever driven a car with a slipping clutch where you got no power to the wheels until the clutch hooked up? Similar to that but shorter than that and it feels distinctly digital, like power is totally off/on.

I am not a professional driver, but consider myself a fairly skilled driver of manual transmission cars, especially BMWs. Over the years I have owned/still own a 2002, 4 different e36 m3s in various states of modification, a built s52 swapped e30, e46 330 zhp, etc. I have plenty of experience driving turbo cars, from super laggy, big-turbo older Porsches to small, fast spooling turbo cars like my wife's f30 328 and everything in between. I was a valet for years and have driven everything under the sun, at least around the block through the first couple gears. From my experience, this issue is totally unique to the M2/M2C (no experience in other s55 cars though).

This ain't turbo lag. It is happening before and distinct from the turbo starting to spool back up. If anything this is causing more turbo lag than necessary because the car feels like it is not allowing the turbo to even begin spooling back up until that 1 second duration is finished, losing more boost all the while. Additionally, this issue is totally non-existent if cruising in any RPM, coming off the gas for a full second and then punching it. The car feels snappy and very responsive as it should, with only (IMO) minimal turbo lag.

This is not DSC/traction control related. It feels like a protective measure that keeps the traction control from even kicking in. Moreover, the DSC/traction light has not flashed yellow even once, which is supposed to happen any time that system engages. I am actually starting to doubt whether this car even has the ability to chirp its tires when upshifting because of this issue! I sure can't make it, though its tough trying to stay below 5500 rpm while full throttle shifting from 1st to 2nd. But with this car's hp and torque figures, it should have no problem barking tires from 2nd to 3rd with a well executed shift. It can't.

I highly doubt it is CDV related, as I have experienced that issue before in my other cars, and this feels MUCH worse/more pronounced to me.

The wide open waste gate theory posted by the OP sounds very plausible to me, the subjective feeling of this issue mirrors exactly what I imagine would happen if the wastegate was just dumping all boost pressure for a second. I have never felt this in ANY other turbo car.

What blows my mind is that in all the research I did on this car, and in all the videos I watched of reviews of the M2C and videos of pitting the M2C vs various other sports cars, not once did any driver mention this issue. The car got glowing reviews in literally every video I saw, and seemed to best every damn car they put it against on track. I did an enormous amount of due diligence before purchasing (my first new car ever). Not a single one of the talented and respected drivers that I watched flog this car around so much as mentioned it, even when pressed to try and find something negative about the car. I find this absolutely astonishing, as I find this issue so annoying that it takes most of the fun out of driving a manual transmission car!! If I was aware of this GLARING problem, it is bad enough that I would have second guessed buying the car without putting in some serious wheel time in one to decide if I could live with it. Its that annoying.

The day I bought it, I let my best friend drive it immediately after we stepped out of his newly acquired '99 M Coupe. His first sentence within a quarter mile of driving my car (carefully and respectfully) was "whats up with that delay every time I shift?". It is that noticeable guys.

I am also mind blown that this was not the very first thing addressed by tuners. I swear if you offered me a tune that fixed this problem but gave me 50 LESS horsepower I would be all over it.

This issue has to be addressed, as it is the only major negative issue on what I would consider to otherwise be an absolute gem of a sports car.

To the doubters, just drive a 6MT for 30 seconds and you will say "ohhhhh NOW I get it".