Backstory:
The time has come, the 6 speed has **** the bed. While it is still able to move the car under it's own power, I don't think it will be able to for much longer. I had some chunks and pieces come out of the drain, and now it is extremely noisy in all gears except for 5th and 6th. I'm not sure what exactly happened, nor do I know if I will find out as I don't have much interest in tearing down the 6 speed. I might just give it away or sell it for cheap if someone has the interest in trying to rebuild it.

Some sort of clip or ring that I fished out of the drain hole with my fingers.

Crunchies

Magnetic Drain Plug

Introduction:
Anyways, in the spirit of being unique and trying something new (as well as avoiding the Kmiata mess that Z_WAAAAAZ had been dealing with), I think I'd like to be one of the first to attempt a ZF 8HP50 swap. For the unaware, the 8HP family are 8 speed automatic transmission designed by ZF. They are the successor to the 6HP platform, and are used in many cars from BMWs, to Audis, to Dodge Hellcats. They seem to be extremely reliable and robust when treated well. They also tend to be under-rated by ZF regarding their torque capacity. Up until the last few years, it wasn't possible to swap these into cars other than what they originally came in. Thanks to transmission controllers from HTG, CANTCU, and TurboLamik it is now possible to swap these transmissions into virtually any car, even carbureted engines.

For my application, I began looking into the 8HP45 and the 8HP50 which are rated to handle 450nm (331.903 lb-ft) and 500nm (368.7 lb-ft) of torque respectively. In practice though, people report running much more than that. If running the 8HP45, that limits the adapter kit to a Domiworks unit, which is of great quality but on the expensive end ($1239 for the 8HP50/70/75, or $1393 for the 8HP45 due to the different torque converter). Another option is the Adamat Adapter kit for the 8HP50/70/75, which comes in at €765.92 or $840. With this information, I started looking for a cheap source for the 8HP50. Turns out the 2017 BMW 430i has an 8HP50Z that can be sources from wreckers for around $500 or so with ~60,000 miles. ~$1600 or so for the transmission and adapter is pretty dang cheap, but that is excluding the transmission mount, the driveshaft, the electronics, transmission cooler, and optionally the differential.

I'd also be using the stock 430i Torque Converter since the 430i has a gasoline engine (the diesels have a much lower stall speed). This would allow for effortless city driving alongside much safer hard launches using the TC to build boost and avoid shocking the driveline. The car is not turning into a drag car or anything specific, just a do-it-all street car. Speaking of street car, I should finally be able to easily eat and drink while driving with an automatic, so that is cool. Oh, and I still plan on putting ~8,000 miles on it per year so I am looking for reliability.

Transmission Mount:
For the transmission mount, it is hard to say what I plan on doing currently since I haven't even removed the stock 6-speed yet (I'm basically only window shopping and planning currently lol). Regardless, I have the capability to make a homemade transmission mount assuming I keep it really simple. Currently, there are not any of the shelf solutions for this transmission in a Miata. Basically, I plan on using some sort of bushing around 60-70A durometer and welding something together that attaches to the bottom of the transmission tunnel.

Driveshaft:
For the driveshaft, a custom unit will have to be made. The original driveshaft is not long enough to have modified to fit. The stock Miata transmission is 33 inches long if my googling is correct, and the 8HP50 without the adapter plate is only 27 inches long.

Electronics:
For the electronics, I plan on using a TurboLamik transmission controller. It would allow me to use my MS2 without being able to auto-blip on downshifts for the time being. I believe I only need to feed it TPS, MAP, RPM, and the brake switch signal. Eventually a Haltech with an electronic throttle body will likely be involved, but for the sake of just getting the car running again I don't want to increase the scope too far. For the shifter, I think I am going to use either a sequential style shifter that is very common or a factory BMW shifter with paddle shifters.

Transmission Cooler:
For the transmission cooler, I believe I will just get a Setrab cooler and mount it to the driverside of the back of the radiator. That would allow me to center mount a powerful Spal fan, and allow for another Setrab cooler to be mounted on the Passenger side for the engine oil cooler.

Differential Solution:
Lastly, the differential. It is a fairly tricky situation since the 8HP transmissions like to blow themselves up when spun over 8000rpms on the output shaft. For perspective, without surpassing 7500rpm on the output shaft (which is still somewhat aggressive, but should hold up if not a regular occurrence) it would be limited to following speeds:

• 4.3:1 ring and pinion: 118 MPH
• 4.1:1 ring and pinion: 123 MPH
• 3.9:1 ring and pinion: 130 MPH
• 3.6:1 ring and pinion: 139 MPH
• 3.3:1 ring and pinion: 152 MPH

Because of this, it would be most optimal to swap in a differential with a final drive in the sub 3.0:1 area. Especially if the car is to be tracked and frequently reach these higher speeds. A hypothetical 2.8:1 ring and pinion would get you 181 MPH top speed, and a hypothetical 3.0:1 would get you to 169 MPH. Personally, I don't really want to swap in another differential if at all possible. The question is: can the Torsen II hold up? Maybe, maybe not lol. I've not 100% finalized what I want to do in this regard other than keep the stock Miata differential housing. I already have a 3.6:1 ring and pinion sitting on the shelf, but with the availability of the 3.3:1 ring and pinion ($800 MFactory R&P from BofiRacing), I think I will sell the 3.6:1 and upgrade to the 3.3:1.

Additionally, since the Torsen differential isn't the strongest unit, I am also considering using the tuned OS Giken differential from Supermiata. Supposedly, these should be able to handle 400whp+ and hard launches. I guess we will find out when I launch the car on boost, with drag tires, and a first gear ratio of 5.0:1 shooting for 1.7x second 60 foot times. From my research, there hasn't been a case where the actual ring and pinion break. It seems to be the Torsen that lets go. Regardless, the Supermiata OS Giken with a reinforced differential housing should be able to handle the launches. Stronger axles will probably be installed too. All together, this should be around $2350 into the differential including the V8 roadsters PPF delete mount. That is assuming I sell the 3.6:1 for $700 and get the Supermiata OS Giken ($1600 by itself).

Conclusion:
I think I have covered most of it. Setting up the TurboLamik and tuning it is really simple from what I've read. There will also be a few little tidbits like the gear indication screen and setting selector **** that I didn't already mention, but otherwise I believe I have a fairly good plan. My goal for accomplishing this is ~6 months, but realistically I wouldn't be surprised if this turns into 1-2 years given how easy scope creep is and how many ifs and buts there are. I went ahead and made this post so that if anyone has any comments or questions that I haven't already asked myself it would help me plan better. So please, give me some thoughts. Especially if you have ever blow up a Torsen II differential (came in 1996+ cars). If I end up being able to use the stock Torsen II, it would save me at least $1600, but if it blows up, it would be even more money down the drain. Currently, I have not purchased anything since I am trying to move apartments and have vacation planned in early November. I'm hoping to purchase the transmission and adapter kit in December if everything goes to plan.

 

First, lol at 8hp swap and MS2.

Second, sub'd for future progress updates.

Thirdly, anyone else listening in, avoid HTG at all costs. Like, OP should delete it from his list of options. The tech is decent but spotty, but support is even spottier and all their tech people are jumping ship. Their social media pages and forums are dumpster fires last I heard.

While I'm at it, I realize 1st-3rd will be very short, 130mph for the 3.9 is not very slow. It's track dependent, but even high horsepower cars are going to struggle to use all of that gearing on all but the faster tracks, and it's about a 11 second 1/4 mile. And 10mph more with the 3.6 requires a huge amount of power once you're limited by the 3.9.

Has anyone actually put an 8HP in a Miata tunnel? Curious on the clearance there.

 

It is a match made in heaven isn't it haha.

This 1000 times over. I would never even consider using one. If it was the only option, I likely wouldn't even consider the swap.

Yeah, you're not wrong. Only point I might make regarding the end of your statement is that as the gear ratios become tighter and tighter, the differential's ratio matters less and less. To help visualize it better, imagine if it was a CVT. The acceleration won't change with a CVT based the final drive. Regardless, I'm not super concerned with the longer final drive slowing me down compared to a shorter one. The ability to shift faster in combination with the tighter ratio gears might should(?) be quicker than stick shift with a short final drive. Also, the lower I can get the output shaft speed the happier I will be. If the internal forces at 8000+ are great enough to crack the housing, the stresses at 6000 or 7000 are still pretty dang high.

Wombat57 was working on it, but it appears like his build has slowed down to a pause currently. I don't think he ever got around to physically testing it in his transmission tunnel. I wonder if we could get him to either take some measurements of his 8HP45 or do a test install for science.
tadeuzagallo fit an 8HP70 fairly easy it seems. I don't currently have the effort to further search through his build thread to confirm that though. It looks like it fit fairly easily, but given that was with a K24 and custom engine mounts. There's the possibility that his engine mounts moved the engine forward enough so that the bellhousing wasn't an issue.

 

From tadeuzagallo's thread:

It seems like the only issue with fitment is how far down the transmission oil pan is. Otherwise it fits fairly well it seems. This is with the 8HP70 too. The 8HP50 should be dimensionally smaller and might not hang as low.

 

Excited to seen the ensuing carnage (or hopefully lack of). While I still like having 3 pedals, a more GT style setup does get me excited.

 

I want a ZF in something I daily ever since we got an Alfa rental and immediately fell in love. Subscribed!

 

I have a back-burner, probably-just-wishful-thinking project to put an 8HP into a buddy's 928 S4. This thread is relevant to my interests.

I'd love to see some measurements when you get your hands on one of these. It's too bad that Padlock isn't closer to you since he's kicking out all these 3D scans right now, that would be awesome.

 

yaaay! more 8HP swaps. Hopefully faster completed than mine. I'll try to post some dims I measured a couple months back on one of my -45's. I have a Motorsports Electronics PnP ECU, and they were nice enough to send me their DBW board that plugs right into the non DBW ECU, and I plucked a Bosch BMW electronic throttle from the local PaP. My next steps are getting the car running on the ECU, then DBW, then COP's, then injectors, then the turbo, then the tranny. So I have a ways to go. And a new grandson.

 

Technically, you can use a third pedal with this transmission. It just requires use of a linear position sensor. If you skipped using a torque converter like Wombat you could probably use it to start/stop. I think I might install one just to make my drift buddies happy. It’s fairly common for drifters to use this transmission and do exactly this.

That was my reaction after driving my cousin’s Hellcat. It’s just so crispy yet smooth.

I wonder if there are any apps I could use on my phone. I’d be willing to pay a couple bucks if need be. A quick google says that my iPhone should be able to do something of that nature.

 

I've loosely been summoned... If any of my scanning services are of value, please let me know.

I've got full unibody tubs (NA & NB) on the list of things to scan (and I know the right people that have them) so things I offer could be of value for this thread at some point.

 

Time for an update :)

Almost all of my plans have now changed. I will no longer be using the Turbolamik with my MS2PNP. I will also be running the larger 8HP70 rather than the originally planned 8HP50 with a MaxxECU Race.

I've discovered that MaxxECU can control the first generation 8HPs with their ECUs after flashing the firmware on the gearbox. Since I want knock control and electronic throttle body support, that limits me to the Race ($1800) and Pro ($3300)ECUs. I don't see any other feature of the Pro ECU that I need other than the appealing 10 more analog inputs, but I don't think I can justify the $1500 considering I don't actually NEED that. Regardless, the Race ECU will allow me to get rid of my MS2PNP and skip over the $2500+ turbolamik controller. It also eliminates having to upgrade the ECU down the road.

Since the 8HP50 is the second generation which the Maxxecu doesn't support, and the Adamat adapter doesn't support the 8HP45, I will have to use the 8HP70. Not a big deal, I've been window shopping online, and they're cheap and abundant if you look for a unit from the right car. It won't change any plans other than decreasing the already very limited exhaust room, more on that later.

The current plan is to order the ECU first thing after the holiday season, get started on the adapter harness, get the car running (just not driving), and then begin the 8HP swap process. This is arguably the biggest project I've ever done with my car, so I'm trying to break it down into small sections to avoid burnout and getting in too deep and getting stuck.

I've got a driveshaft shop picked out, and I think I am going to try and use CV joints instead of U-joints on the driveshaft to avoid having to worry about the U-joints angles/transmission angle. I still need to discuss it with them, but I wanted to wait until I was further along before calling and bothering them.

Another large concern is exhaust room... I'm very doubtful that the Kraken kit will fit at all. Since my hood is currently dented from a deer, I think I may just temporarily make a hood exit when the time comes. Eventually I'll either attempt to make a downpipe/midpipe that fits myself or take it to a fabricator. I like the quiet Kraken kit, but I want to drive my car more.

I've completely moved into the new apartment, so now it is time to start utilizing the garage. I've still not purchased anything, but I promise I'm not just blowing smoke up your asses. My next post will be when I have the MaxxECU in my possession :)

Here are a few relevant videos if anyone is interested:

 

Watterson - I just saw your direction change - I'm still moving slowly forward on my 8HP swap - with the -45, also in a '99. Interesting about the Maxx ECU - I haven't read much about it yet - do you have any idea whether it can manage the clutches like the TurboLamik? If you don't know off the top of your head - don't worry, I'll do some checking too, just being lazy in case you already know. If I could save the $$ on the TL by using the Maxx without the torque converter I might go that way too.

Thx

Wombat

 

Watching with interest. The 8HP swaps were just starting to build momentum when I committed to a K swap. I don't think it would benefit me at stock K24 power levels, but if I ever decide to turbo the K and up the power, the 8HP is very interesting indeed. A really good auto/paddle shift can be a huge benefit on track...

Best of luck with the project!

 

I could be mistaken, but as far as I’m aware clutch based take up and clutch kicks require replacing the factory mechatronics controller. That allows the TCU to directly control the solenoids. The MaxxECU controls the transmission by flashing the firmware with a custom tune.

On MaxxECUs website they state that they’re “looking into” it the possibility of adding these features later, but that was posted in 2023 I believe. It says that they would look into it in 2024, but I’ve got a feeling it won’t be coming out this year lol. https://www.maxxecu.com/webhelp/adva...e_control.html

 

Any updates on this? Why not use something like HP tuners to tune the transmission? What power level were you making when you killed the 6 speed?

 

HPtuners not having the capability to tune 8HP's as a standalone probably has something to do with it....

 

I just spent $600 on tools at Harbor Freight to support the job. Now that I have my own garage I had to buy things like a jack and jackstands as well since I don't want to steal my grandfathers. Possibly pulling the trigger tomorrow on the Maxxecu, not 100% sure. Might be another 2-4 weeks. I've technically got the money to do it now, but I don't want to possibly have to dip into my savings if an emergency expense popped up. If someone would buy my ECU, Torsen diff, and that stuff I'd pull the trigger.

Also, Padlock is right. HP tuners doesn't support the 8HP, plus I'm practically deadset on the Maxxecu due to the insane amount of flexibility that their ECUs allow for.

Virtual Dyno is attached from the tune that blew my 6 speed. Some of these pulls were with brake boosting to get the turbo spooled early as possible so low end torque numbers might be a little funky.

 

Actually, it appears like HPTuners can do some 8HP control, but I don't think it is controllable with their full standalone. I think their 8hp control is basically just flashing the transmission with new data regarding the shift points and torque calcs. I could be wrong, but it doesn't seem like it is on par with Maxxecu. It is my understanding Maxxecu is the first and currently only company offering the full control from a standalone and stock transmission controller electronics.

 

HP tuners has supported the "ZF" series in the Stellantis line since....2017. Requires seperate TCM flashing for credits. I've seen multiple companies pop up offering standalone controllers. What I don't know is what signals it needs off canbus from the ECU, probably at a minimum throttle input, rpm, speed.

Shift timing, torque management, converter slip, general shifting characteristics. Now what I don't know is the protocol and what is required for sharing, but I do know there are a few companies out there that have cracked that code. Still exciting times and will watch this closely. My targeted 250hp on the 6 speed should last a long time based on research, but love to see these sort of development efforts.

 

That is making some jam! 100 more than I'm targeting for the sort of racing I'm looking to do in this chassis. I bet the 8hp drastically improves your lap times as well. I think the Maxx ECU is a solid option and provides a lot of flexibility. It's one of the few standalone brands I haven't used actually, but looks very promising on the surface. Please keep this thread rolling!