Two months ago today, I began tearing down my 135i in order to remove my failing stock turbos and convert the car to a single turbo using ACF's N54 kit. Three weeks later, working on and off during my spare time, the install was complete. Over the subsequent five weeks between that first fire up and now, I've racked up 3,750 miles of use, broken in the clutch fully, learned how to drive the car over again with all the new hardware, and had to iron out the inevitable kinks involved with a project of this magnitude.
Since I had some free time today, and won't have much in the foreseeable future, I took the opportunity to take advantage of the nice weather and perform my annual polish and wax. Even though this car is a daily in all sense of the word and has spent every day and night outdoors for over two years now, I still like to keep the exterior looking mint. And since I'm transitioning to shorter oil change intervals now that I only have one turbo, even though it had been less than 4,000 miles and only 5 weeks since the N54 had gotten some fresh Motul and a new Mann, it was also time to do my first oil change.
I've already detailed the steps I use to paint correct and seal my car earlier in my build thread, but after buffing diligently for many hours, I had something to show for my hard work. Not too bad for now having over 106,000 miles on the odometer.
After spending so much seat time in such a short time, and in my previously used "stream of consciousness" style, here are my thoughts on owning a single turbo N54 135i, and in particular the 6062 ball bearing PTE turbo using AC Fabrication's kit:
- For the first two weeks of single turbo life, I was plagued by o2 sensor issues. I had purchased and installed ADV sensors specifically for this conversion, but for whatever reason, I could not get them to cooperate with my IJEOS ECU. After pulling my hair out over possible culprits, I finally installed a set of NTK o2 sensors and my problem was solved so I could start enjoying the car. Those NTK sensors haven't skipped a beat since.
- The Spec Stage 2+ clutch proved problem free while breaking everything in, and it was quite easy to learn the new engagement points. In comparison with the OEM clutch, pedal pressure has increased slightly, and everything grabs a bit harder once it reaches the engagement point. All in all, I don't have many complaints about my clutch choice. The combination of the UCP, shifter mods, and lack of a CDV, make gear engagement buttery smooth.
- The MFactory steel SMFW on the other hand, has been the aspect of this build I've been the least keen on. Using MHD to raise the idle of my car to 950 has kept the "marbles in a can" sound many describe at bay for the most part, but this can be still be heard slightly with the AC on or if RPMs dip while taking off from a stop in 1st gear. While this is very easy to live with, the noticeable NVH caused by the SMFW at low RPMs in first gear was somewhat disappointing and surprising. This gets worse after shifting into 2nd gear after the RPMs fall again and low throttle is applied. That NVH during low-speed driving has been my biggest gripe yet, but doesn't manage to ruin the entire driving experience. Hopefully in the future, we'll have an option to ditch the SMFW and high HP misfires.
- I've closely monitored engine activity through the JB4 Mobile App, and shared a bunch of the logs I've collected across numerous forums to get feedback and make sure things were looking okay. I had intentions of running an ethanol blend for added safety and more power, but as I progressed the wastegate spring boost of 15psi up to map 2's 17psi, it wasn't long before I saw I was running out of fuel from the HPFP side on E30 fuel at 17psi. Since then, I've tapered back the fuel to E25 to take some stress of the HPFP, and opted to just daily drive on 15psi. For the time being, I'm content with running this low boost map, but more than likely I'll add one of the upcoming intake manifold upgrades with integrated port injection once I get bored at this power level. For the record, things feel far faster at 15psi through the 6062 than 20psi + inlets felt through the stock twins.
- The Phoenix Race FMIC is pretty unbeatable it seems. I've yet to see a log where IAT hasn't went down during a pull. My VRSF 7" non-HD FMIC would result in a large increase over a multiple gear pull when I was FBO. I'm also enjoying the stealthy black finish I gave it before installing.
- By pairing the same catless N54 midpipe with Vibrant resonators and MadDad Whisper axleback that I'd been using for a while now with all the new single turbo hardware, the exhaust note is much improved. At idle and during normal driving, things are very tame. But any heavy application of the throttle and all hell breaks loose. Airplane style spool up sounds, a terrific throaty growl out of the rear end, and external wastegate dumps that make me smile every time. Natural run over or "burble" isn't as audible as it was with the twin turbos; not sure of the cause of the reduction--I've never used the MHD option and don't intend to. The common comparison to the 2JZ exhaust note from single turbo N54s is not exaggerated, they certainly share similarities. For a daily driver, I wouldn't change a thing sound wise. Plus no there's no sound pollution from rattling wastegates, nor do I have to worry about there being any in the future.
- On the topic of being a daily driver, switching to a single turbo has only seemed to improve overall functionality and fun. Since the conversion I've been averaging 21.9 miles per gallon on a variety of low percentage ethanol blends between E20-E40. Oil temperatures are consistently lower. The large amounts of smoke and terrible smells of burning oil I used to be embarrassed by regularly are a thing of the past. There are no lights on the dash, and no functions were lost during the conversion. Drivability with the BMS ST E85 TS THR BEF is even better than I thought it would be, and the cruise control feature is even smoother than it was with the OEM twin turbo configuration. Four days a week I take this car on a 3 hour round trip, and it hasn't hiccuped once. Earlier this week I drove the car for 7 hours straight in a variety of different driving conditions with nothing negative to note. I'm impressed.
I need to pick up a GoPro in order to get some better in-car footage, but here's a quick video I was able to make this afternoon including some start up action, walk around, some idle/revs, as well as a quick pull at the end . I wanted to get some audio of the exhaust at full throttle, as well as the external wastegates, so please excuse the fact I had to use my front facing iPhone camera to do so.