[jq_f22]

This is going to be a long one so grab a snack.

The ZFHP45 Transmission supplied by the factory in N55 powered vehicles from everything from the X5 to the M235i is great there is no doubt about that, developments by RBT-Tuning make it as fast as a dct while still great to daily drive. The problem is its ability to cope with high tq applications. While for years people have stated it is not needed to upgrade, those applications have more than likely not seen real high levels of torque or the amount of strain that drag strip runs put on a car. The factory HP45 should absolutely not be considered a long-term solution for anyone pushing more than 550lbft at the engine in my opinion.

I discovered this quite quickly on my path to getting a 10 second run out of my m235. Towards the end of my e85 tune revisions, I started noticing a hesitation in 2nd Gear when launching, a pause in acceleration. I thought nothing of it at first and kept on my merry way after all the car was on XHP stage 3 with the additional line pressure increase, it had its service done preventively and everyone on the forums that ever asked the question "how much will a HP45 hold?" was met with immediate reassurance that it was overbuilt and its 330lb-ft/450nm rating was underrated, so why not trust what people on the internet said, right? Well, what happened next was fun. Next data logging trip out I ready the car for a launch, all fluids up to temp including the transmission, brake boost the car up to 2800rpm let off the brake, full on the gas and immediate transmission malfunction. The transmission shifted on its own into fourth gear. The transmission was fine with normal driving, setting a 550lbft limiter in XHP helped a little with the issue. It took a launch no problem on my 93 octane map but would no longer hold full power from a launch on the E85 map. I hit a wall with my goal. The car had managed an 11.29 but that was still far off from a 10 second run. 60 ft times were also not very consistent as well ranging from high 1.6's to high 1.7's. So what did I do?

I considered a rebuild from pure drivetrain but something bugged me. It would still be a HP45. Meanwhile, with the rapid development, the B58 platform has seen since its arrival many have already been plagued with their hp50 giving them issues or giving out as a whole. I remembered reading a thread a while back in 2019 by F30MGM https://f30.bimmerpost.com/forums/sh....php?t=1663852.
They had swapped a European spec 330D Transmission into his RWD 340. The N57 and the B58 have the same bell housing it bolted right up. The HP70 is rated for 516lbft/700nm from the factory. So if HP45 could hold well over its factory rating what could the HP70 hold up to? The thought lingered but I knew that the bell housing on the B58 was different than the N55/N54. So I dug into the internet, most of you probably already know that Alpina made a twin-turbo version of the N55 in the F3X chassis named the Alpina B3.



Alpina did not think the HP45 was sufficient as well even with their conservative power figures, so what did they do? Special order a HP70 from ZF with a bell housing that would mate to the N55? No.

They fabricated a transmission adapter! So easy right? Go down to my local dealer and order a Alpina only part right. Obviously, this was not an option so the search began again until I stumbled upon DOMIWORKS Engineering in Sweden. Daniel there created a beautiful adapter out of a solid piece of aluminum very similar to the Aplina part.


I bit the bullet, ordered the adapter, found a HP70X pulled from a 2018 330D, long term journalist vehicle over in Germany that had been totaled with 20,000 miles, and got to work. Daniel advised me a spacer between the torque converter and the flexplate might be needed as this specific application had not been tested when developing the adapter.

The work starts!

Getting the transmission out of one of these cars is just like any transmission job in a BMW with a few extra steps for xDrive owners:
-Drain the transmission of fluid.
-Remove the complete exhaust.
-Remove front and rear driveshafts.
-Unbolt the torque converter from the flexplate through the access hole on the engine block.
-Unbolt the transmission support brace to allow for access to the top bell housing bolts.
-Disconnect the TCM and transfer case computer connectors.
-Support the transmission with a transmission jack.
-Undo the lower bell housing bolts.
The HP70 and the HP45:

The HP45 Bellhousing:

The HP70 Bellhousing:


As you can see from the above the bell housing of the two differs not only in bolt pattern but in starter location, another key difference is that oil cooler line ports on the HP70 are smaller than the HP45, 18.2mm vs 16.4mm. Both of these issues are easily taken care of with a quick visit to your local metal fabricator/machinist. A buddy's shop took care of this for me in half an hour.



A test fit of the adaptor:



Remove the transfer case from the HP45 and bolt it onto the HP70. RWD owners obviously skip this step.


Next, I measured the HP45 bell housing to the torque converter to compare to the HP70 with the adaptor and see if a spacer would be needed, in the hotrod world simple washer like spacers are used to achieve the correct spacing. The HP45 torque converter is reused as the HP70's is too large in diameter to fit. Once measured the difference turned out to be only .2mm well within the .7mm of tolerance conveyed to me by Domiworks, no spacer needed! Installing the HP70 is just a reverse of the uninstall, everything plugs and bolts in like factory.



Next is the ISN reset on the new transmission, I used Bimmerscan for this https://bimmerscan.com/. Bryce over there is great and answered any questions I had about the process. After the transmission is mated to your car a custom map is required to have to operate correctly for the powerband of an N55 vs the N57 it came out of. Of course, for this I used XHP. Christoph RBT-Tuning (contact:460118) took care of me quickly and the car was up and running.

Next up was the first drive, I was surprised, to say the least, the HP70 seemed to shift quicker and firmer than the HP45 on Stage 3/Stage 4 OTS. Power delivery was seamless, no strange vibrations or noises. My first launch left a grin on my face, smooth power delivery in all gears, no pause, no hesitation. The car was finally able to put all of its power to the ground. 1.5x 60ft's became the new norm. Once my E85 tune was finalized by CaryTheLabelGuy the goal of a 10.9x was realized and the car did it consistently.



If anyone has questions feel free to ask below!

[imperfectluck]

Really enjoyed the story and the lengths you went to figuring out the best way from the sourcing of an Alpina transmission to the end result. Certainly was worth the good read and happy to hear the end result was met to your expectation.

Love the hoops and ladders us in the community go through to make such things possible.

[Pussiwillow]

Wow
Just wow.
This is a great read. May I ask an approx you have invested in this swap, any reason you didn't go dct? Seems it's becoming more doable, I've been tossing the idea between what you did and a dct, I prefer the zf8 over dct, I just feel they're so much smoother obviously per design. But just wanted to hear your reasonings. Looking up the adaptor now

[jq_f22]

Originally Posted by jq955

Thanks! The dct isn't really an option for xdrive owners due to the transfer case. I would say about 2.5k is in the HP70 setup so still much more economical than a dct, I too prefer the ZF8.

Thanks! The dct isn't really an option for xdrive owners due to the transfer case. I would say about 2.5k is in the HP70 setup so still much more economical than a dct, I too prefer the ZF8.

[Pussiwillow]

Originally Posted by jq955

Thanks! The dct isn't really an option for xdrive owners due to the transfer case. I would say about 2.5k is in the HP70 setup so still much more economical than a dct, I too prefer the ZF8.

Oh durp I totally forgot about x drive
I'm rwd so I'm ignorant lol
That's honestly not bad at allll, I'm actually shocked that's bad ass

[n55david]

total cost?

[Pussiwillow]

Originally Posted by Phantom10R

total cost?

He said approx 2500, not bad huh?

[Possessed]

Very cool and great read!

[ctt300]

You are a madman and I love it! Big props to your ingenuity and great final result.

[TooHighPSI]

Congrats, and thanks for the write-up! Did you have to lengthen your front driveshaft, and shorten your rear driveshaft? Or is the adapter thin enough that you did not need to?

[Boostedphil698]

Still don't understand why you didn't build the HP45 with Pure when they offer a stage 1 package. I'm sure the swap is less expensive than a trans build.

[LA1Z24]

I am also curious about the driveshaft. It does not appear that the ZF uses a slip yoke.

[AmuroRay]

This is SO awesome, and I'm a manual driver. Guys who can, do.

[jq_f22]

Originally Posted by TooHighPSI

Congrats, and thanks for the write-up! Did you have to lengthen your front driveshaft, and shorten your rear driveshaft? Or is the adapter thin enough that you did not need to?

You're welcome. No changes are needed to the driveshaft!

[jq_f22]

Originally Posted by Boostedphil698

Still don't understand why you didn't build the HP45 with Pure when they offer a stage 1 package. I'm sure the swap is less expensive than a trans build.

Yes, roughly 1/3 the cost of the Pure stage 1 HP45.

[Boostedphil698]

Originally Posted by jq955

Yes, roughly 1/3 the cost of the Pure stage 1 HP45.

Aren't the shifts slower in the diesel trans?

[jq_f22]

Originally Posted by Boostedphil698

Aren't the shifts slower in the diesel trans?

Why would you assume that? The HP70 is used in plenty of gas-powered vehicles from other manufacturers.

[NEWTRON]

Originally Posted by Boostedphil698

Aren't the shifts slower in the diesel trans?

That's irrelevant with the custom xHP tune.

[thejeremyman9]

Originally Posted by Boostedphil698

Aren't the shifts slower in the diesel trans?

As noted above the shifts are come down to software programming, not hardware or which car the trans came from. Same reason why the ZF trans behaves totally different between manufacturers and when on OEM software vs XHP.

[jq_f22]

The HP70X is up for sale for anyone interested.https://f30.bimmerpost.com/forums/sh....php?t=1888570

[Kdebraux]

Does anyone know if it has to be a hp70 out of a bmw or can it be any hp70?

[jq_f22]

Originally Posted by Kdebraux

Does anyone know if it has to be a hp70 out of a bmw or can it be any hp70?

HP70 out of a N57 powered BMW.