If you're not interested in reading the whole post, then in summary, do not tune your supercharged Z4M with anyone other than Josh from Severn Tuning. Trust me.
This is a long-overdue post. I purchased my 2007 M Coupe back in the fall of 2019 with the intention of supercharging it. Naturally, I started my research by reading this forum. Still, I had many questions and many of you pitched in (thank you all once more). The most help however came from Josh
pokeybritches. Not only was he very experienced, but he took the time to answer all my questions, asking nothing in return. He said he also had a working tune for the car but I opted to find someone local as I had this idea in my head that the people doing the work on the car should all be local. I decided to go with TTFS (Frank Smith) because he has a great reputation in the BMW community and he was fairly local (about an hour's drive). Frank tuned the car, first dyno it put down around 550 at the wheel. I was stoked, this thing was a beast!
Car ran very well on the dyno across the entire power-band. Then I took her out for a spin and went for a hard third-gear pull, power cut out and car went into limp mode. Took it back to Frank, he tweaked the tune, put her on the dyno again and she ran very well. Took her out for a spin, same problem. WTH? Made another visit to Frank, he said he was getting static-y readings from car and was unable to tune any further, suggested I take her to a shop to check supercharger wiring. Shop said they found a miswired cable, they re-wired it correctly and I took it back to Frank. Readings were fine and he did some work and dyno'd her again. Again she ran well on the dyno but went into limp mode when on the road. Unbelievable! It also started stalling when coming to a sudden stop from high speed. Car was just not derivable. I took her back to Frank, same result. This must have happened at least five times, maybe closer to ten. I was getting frustrated and so was Frank, he absolutely hated this car. Not only did it have this annoying issue, but due to the ECU serial connection on this model, it takes upwards of 15 minutes to download or upload a tune so there was a ridiculous amount of wait time in a day's worth of tuning. It drove Frank so crazy that at some point he suggested the car needed high octane fuel, to be poured over it and burned
After many visits over the span of two years, Frank finally gave up and concluded that this must be a mechanical issue as he saw nothing wrong with the software. I must mention here that Frank was very patient and took his time with the car, despite having pressing, non-work priorities at the time. He tried his best. He also did not want to accept payment for the follow-up tunes and dyno time but I insisted. He recommended I take the car to a reputable shop to look into this suspected hardware issue. Two years and over $20,000 worth of mostly speculative mechanical work later, the limp mode issue persisted and car was still not derivable. Car spent most of the first three years in the shop or getting worked on. It was heart-breaking.
I was at the point of giving up and dumping this project but decided to reach out to the Z4M community one last time. I posted on this forum and reached out to several people who ran supercharged setups like mine. I quickly found three folks who all had the same exact issue with limp mode and with stalling upon coming to a stop. They all had one other thing in common, a TTFS tune. They told me they struggled with this issue for a while until they ran across Severn Tuning who gave them a working tune. I was skeptical and really did not want to spend another $1200 on a tune but I reached out to Josh and he told me he was confident his tune would fix the problem. He emailed me the tune and flashing instructions.
I flashed the Severn tune right there in my garage and took the car for a hard spin. No limp mode. Car was idling perfectly and running very smooth across the entire RPM range. Still being skeptical, the next day I took her for another hard spin, many red line pulls at max boost. No limp mode. It’s been over a year and the car has been running flawlessly, even that stalling upon coming to a stop issue never came back. To further optimize the tune for my car, Josh had me conduct several logging sessions and used the data to further improve the car's performance. Car runs better than new now.
In addition to Josh's excellent tuning knowledge, he is also very responsive and takes great care to ensure that his client is fully satisfied. Thanks to Josh, this multi-year nightmare is over and I was finally able to enjoy my supercharged Z4M. If you plan to supercharge your Z4M, then Severn Tuning is the way to go.