Hi all,
Documenting my swap from my factory 6MT (S6-53BZ) to an 8P70H because I don't see any good build threads around. It's internally similar to an 8HP70, with one difference covered later on in the thread that means you will have to open one up if you want it to work. No, 8P70H is not a typo, it's not an 8HP but is instead an 8P, because from the factory it does not come with a hydraulic torque converter and instead a clutch pack and electric motor (which we will be swapping out for a torque converter anyways). The first post will be a lot of the build plans, theory and information I have collected along the way through RealOEM, TIS, and comparing internal parts listings on eBay for part numbers, so if you want to get to practice, skip to the second post. If anything here is wrong, don't hesitate to speak up, I want this to be 100% correct for a point of reference.
This one won't quite be your regular 8XP70 swap, as I'm planning on keeping both the clutch and the H-pattern (I'll get to this later). I'm also using an N55 ActiveHybrid 5 8P70 rather than the usual N57 8HP70 + adapter plate solution. I'm not 100% sure that it will work, but so far everything I've seen indicates it should. The input shaft seems to be the same as an N57 box, the oil pump is the same PN, and the valve body also seems to be the same PN with a different revision between 2 other regular HP70s (-598 vs -426 and -666).
The N55 8P70 also seems to be the same length as the N55 8HP45, meaning I should be able to use a factory N54 flex plate with a factory N55 8HP45 torque converter (assuming input shafts between HP45 and 8P70 are the same diameter and spline layout) and spacing should be perfectly factory with no adapter plate nonsense. It is about 25mm longer than an S6-53 and a hair longer than a 6HP21, so we will be using a 335D driveshaft which is 6mm shorter than the auto driveshaft. It interestingly also has the 8HP45-sized 18mm cooling channels if RealOEM is to be believed, so I can grab an HP45-AN adapter from Domiworks and run some braided line to a 10-row oil cooler mounting where the 335is auxiliary cooler would go. We'll see how it goes with no thermostat.
Let's explore the ActiveHybrid 8P70 gearbox as well because there really is not much information around on these at all. There are 5105 total ActiveHybrid3+5+7s in the world, with 1592 in the US and 3513 elsewhere. This makes the gearboxes REALLY hard to find in the US. When I bought mine, there were 4 total gearboxes listed in the US (3 for $1900-2600 without the HCC, and mine for just over $700 with HCC and 83k miles, absolute steal!) and none anywhere else worldwide. The first generation AH7 (2009) is also completely different, it's actually an 8HP70H which has both a converter and motor, plus it's an N63 box, so that won't work for us.
Those of you that are keen-eyed will notice right off the bat that this looks... familiar but different. I know, it's dirty, I'll pressure wash it this weekend. For one, there are 2 connectors on the left rather than 1, and there is another on the right. Well, the bell-housing connector should be rather apparent - it's connected to an electric motor sharing a housing with something called a hydrodynamically-cooled clutch (HCC). It's not a torque converter, but instead a huge clutch pack that must be controlled similarly to a DCT. If you know anything about AMG MCT, those also use a similar design.
It has 2 sets of internal splines compared to the usual 3 we see on 8HPs, but otherwise has a normal-looking 8HP70 input shaft and bell housing.
Let's look again at that extra connector on the left.
This connector confused me at first, but BMW described it well in the "Drive ActiveHybrid" functional description. Regular 8HP-HIS (boxes suitable for start-stop) have a pressure accumulator so it can actuate solenoids and select gears while the engine is off. There's an additional challenge here with an HCC - without oil pressure, the clutch pack is unlocked and the input shaft doesn't spin. Because oil pressure that locks the clutch pack comes from the input shaft spinning the mechanical oil pump, it's a bit of a chicken-or-egg situation. Therefore ZF/BMW has chosen to replace the accumulator with an electric oil pump to both select gears while the HCC is unlocked, and provide the HCC with the pressure it needs to lock, and that's what that connector is for. Cool stuff!
Obviously because we are running a conventional torque converter that's always spinning with the engine, this is no issue for us.
Okay, it's time I explain how I'm doing this whole H-pattern+clutch thing. I'll be gutting the factory TCU and soldering it up for a TurboLamik TCU, which provides clutch-by-wire for 6HP and 8HP out of the box. They integrate well with our E90s and show up to 8 gears on the dash like factory, transbrake, support multiple programming modes, auto-learn, do everything over CANBUS including torque reduction (and blips coming very soon), basically a dream for those that want their gearbox to act exactly how they want it to, and still act like it came from the showroom floor. Really cool stuff!
What it doesn't support out of the box is an H-pattern. That burden falls on me. For this I've chosen an ESP32 because of how insanely cheap and powerful they are. I know they aren't automotive rated and the 3.3V operating voltage may be interesting, but I should be able to map the Lamik to accept 0-3.3V for all necessary inputs and outputs, or worst case make a simple voltage divider. I'm writing a Lamik library in Rust and will be using it in a modular fashion to interface with the TCU. It'll read what it needs via analog inputs with an ADS1115 ADC as well as CANBUS with a transceiver, and have a nice little OLED screen that will output everything we want to know. That'll all be open-source and I'll publish the repo link here once it's ready for consumption along with a PCB that will make things easy!
Of course, you can't shift an H pattern into "automatic." That's why I also bought an LCI steering wheel with paddles for sub-$200 and of course I wanted the ergonomic shape.
The ESP32 will define the behavior, and I'm still working on defining the behavior. The H pattern will always override the paddles, but the paddles will handle shifting from Neutral to Reverse (left) to Drive/P1 (right) to Sport/P2 and finally to "M2"/P3. Holding right paddle will go back to drive, and holding both will activate our favorite feature, transbrake. Park will act like a DCT M3 where it will do it by itself when you shut off the car. At any moment you can start using the H-pattern which will probably select 2-7 because 1 will be utterly useless. The ESP will send upshift/downshift signals to the TCU which will hopefully handle skip-shifting without delay. Maybe I can convince the guys at TurboLamik to add proper support if it turns out well, so far they seem hesitant.
The H-pattern itself will be tough. I could 3d-print some retention mechanism and design some fancy potentiometers but I am thinking a really nice sim shifter might do better in the end, with some 3d-printed adapter for my factory shift knob. That's where you all come in - does anybody have a sim shift apparatus that has really nice effort and feel?
This all sounds great in theory, but let's get into practice!