ZF 8HP Conversion

ZF 8HP Conversion

The problem

More power = More problems
Who could have known..

My 1.8 EUDM NC came with a 5-speed transmission which suits the car well. Light weight, typical MX5/Mitata shift feel and can handle the 126hp for a million of miles.

In 2013 I got a 6-speed from a 2008 NC 2.0 in preparation for FMSC power but also better close ratio gearing. The 6-speed has served me well the last 12 years. Hundreds of laps with 12 psi FMSC on different racetracks. 3 x Nurburgring trips, autox and general hooning

But once you apply >300 Nm on the track stuff starts to break. Like when you add an EFR7163.

Fiveopac over at m.net has an excellent thread on the subject.
First sign is notchy shifting from 3-4 due to the clutch hub starts cracking. Next sign is a big bang of sorts. I got the 3-4 shifting problem after my 3rd trackday with the new FAB9 EFR.

The alternatives

What are the alternatives for a 6-speed manual transmission that can:

  • reliably handle 500 Nm of torque
  • 6-speed
  • Compatible bolt pattern or adapter for LF engines
  • No more than $3K including clutch, adapter and prop shaft

None.

At the time of writing:
SPS offers some upgraded options $5K from Germany (exchangeable core).
Fab9 is working on a Tremec TKX 5-speed. Probably ending up $5K
Custom BMW 330 or E46 M3 transmission as used in KMiata swaps.

With shipping,tax ~ $7-8K

Thinking outside the (manual) box

Modern automatic transmissions (planetary gears and TC) can not be compared to the pre-millennium old slush boxes of the past.
ZF8HPxx series of transmissions are now found in all kinds of rwd cars from 2013- and can with some persuasive software flashing/programming almost give DCT level of shifting speeds and handle +500Nm of torque.
Some quick pulls here

There are now several ECU’s and standalone controllers that can control the 8HP and even add new functionality like manual clutch support and trans brake. Currently here in Europe you can get a used Gen1 8HP45 and 70 for ~ EUR 400-700 (Poland/Latvia)

Checkout Tracktuned conversion on his K-NC https://tracktuned.uk/8hp-gearbox-controllers/ and his other site dedicated to 8hp data: https://8hp.info/

The plan

Since I already have a MaxxECU EMS that has Gen1 8HP control I will use a 8HP45 out of a BMW N20. Straight from rrr.lt via Sweden for some free EU shipping benefits.

The bracket that mounts the box to the BMW floor/tunnel might be reusable. I know several people including one here in Norway that has successfully adapted an RX8 subframe to the four mounting holes at the end of the box.

But… not sure how that works out over time. On the MX5 trans the PPF is “clamped” around the top and bottom of the tail housing which seems to spread the load over a larger area rather than four horizontal holes at the end of the box.

For adapter I will use the Duratec one from https://www.adamat.com.pl
Very high quality work and great service. They actually did not have a flywheel adapter for the N20, but offered to make one.

For controlling the TCU I will use the built in support for 8HP control in the MaxxECU Race EMS.
Instead of just tweaking the maps in the existing TCU firmware they actually flash a complete new software to the TCU which enables new functions and a more direct control of actuators, clutches and whatever magic is going on inside.
To make this work connecting via CAN is not enough, so a flashing tool is needed. It can be rented though for 150 EUR…

But… it only works on Gen1 TCU’s, and not all of them, that would be too easy.
There is some guidance here
I have not found a way of 100% identifying TCU id based on external markings or labels, so to be sure I opened the box and verified the markings on the chip.

Another key component to make this work is a custom drive shaft. Since Paal already did the swap, I ordered the exact same setup from Powertrain.no . His setup has zero vibrations which is important as I know several people who have been fighting unwanted vibrations in drive shafts and axles for years regardless of efforts.
I was a bit shocked of how massive it is though “It’s what we use for 1000hp Supras….”.
10.7 kg, vs 5.4 for the OEM. Not sure ho that impacts things. Mass is pretty near center compared to wheels, brakes, flywheel, but still a hefty chunk of metal.
Adapting the existing drive shaft might be possible, but not that straight forward since it’s shorter.

As for other parts:

Transmission cooler and adapter. I opted for a smaller cooler which I will try to mount under the car.
I already have the engine oil cooler in the left fogligth and plan to have an air filter in the right one.

BMW shifter + harness.
I will get hold of a NC Auto wheel as well for paddles.

So, a pretty involving project.
I still need to get hold of one more “item” before I can start assembly and fabrication, but more on that later.

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8HP45 MX5 Mazda NC conversion transmission