Why the ZF 8HP Is Perfect
for Your E9x LS Swap

Everything we know about running the ZF 8HP behind an LS in the BMW chassis, on one page: which donor to buy, the adapter and converter story, mounting, cooling, wiring, the TCU flash, and how it drives. We run this combo on our own cars.

Why Choose the ZF 8HP?

• Eight gears from a 4.71 first to a 0.67 eighth, just over a 7:1 spread. It launches hard and still cruises under 3,000 rpm on the highway.
• ZF quotes ~200 ms shifts. With paddles it feels closer to a DCT than a classic automatic.
• The 8HP70 is factory rated at 516 lb-ft, stock units commonly live at 600 to 800 lb-ft, and built boxes go past 1,000. See power limits for real numbers.
• MaxxECU control unlocks a transbrake, launch control, kickdown, and up to 9,200 rpm on the factory mechatronics, without opening the valve body.
• It fits the E9x/E8x tunnel with our mount and crossmember, without touching the floor.
• ZF and Stellantis built millions of them for BMW, Dodge, and JLR, so cores and service parts are everywhere.

Picking Your Donor

Rule number one: buy a Gen 1 box. MaxxECU controls the Gen 1 8HP45, 8HP70, and 8HP90 only. Gen 2 units (8HP50, 8HP75, 8HP95, and Chrysler's 850RE) are not supported. Some applications switched to Gen 2 around 2019, notably the new-body Ram moving to the 8HP75, while others stayed Gen 1 for years after, so check the model tag on the left rear of the case before you pay for anything.

Rule number two: buy a Dodge case. The 8HP bellhousing is cast into the case and every brand has its own bolt pattern, so a BMW or Jaguar 8HP70 will not work with the Dodge-pattern adapter kits. The whole LS adapter ecosystem is built around the Hemi-pattern case.

Within the Dodge family, the cases differ in ways that matter:

Two more things to check on any donor. First, the torque converter pilot: 2013-2017 converters use a 34 mm small pilot, 2018+ use a 46 mm large pilot. The adapter kits include pilots for both, but aftermarket converters like Circle D are built around the 34 mm small pilot. Second, skip the 845RE behind the 3.6 Pentastar. It looks like an 8HP45 on paper, but nobody has a straight answer on how much it shares internally, and the V8 boxes are just as cheap.

Buy a running-condition pull with reasonable miles, then service it before it ever sees the car: pan, filter, fresh fluid, and reseal the mechatronics sleeve while it's on the bench. More on that in cooling and fluid.

What You'll Need

Adapter, Flexplate, and Converter

The adapter kit bolts the Hemi-pattern 8HP case to the LS block and adapts the converter to your flexplate. The Dodge torque converter stays, there is no GM converter option. The kit's converter adapter bolts the Dodge converter to a standard GM flexplate, so nothing gets machined and the stock LS flexplate is retained.

• Flexplate: OEM GM or aftermarket LS flexplates work, in the common 3-bolt 10-3/4", 3-bolt 11-1/16", and 6-bolt 11-1/2" patterns.
• Crank spacing: most LS engines are short crank and use a dished flexplate. A few early Gen III engines are long crank and use a flat flexplate. Never run a dished flexplate on a long crank, and a flat flexplate on a short crank needs roughly a 0.405" crank spacer. The kit covers both, just order the right version.
• Converter pilot: pilots for the 34 mm (2013-2017) and 46 mm (2018+) converter noses are included. 2018+ converters need minor modification.
• Starter: on Ram and Durango cases, smooth-nose Gen III/IV LS starters and the later Camaro/Caprice/G8 starters bolt in with no modification. On Charger/Challenger cases, plan on minor trimming or run an unshrouded high-torque starter.
• Hardware: dowel pins for both the GM and Dodge sides, grade 8.8 and 10.9 hardware, and red and blue threadlocker come in the kit. Index dowels set the alignment so you don't have to eyeball it.

Optional clearance mods worth doing while the box is out: grind the unused bolt bosses off the bellhousing for tunnel clearance, and on naturally aspirated cars with long tube headers, the left starter bubble can come off for header room.

Mounting and Driveshaft in the E9x

• Crossmember: the LSe9x DCT/8HP crossmember carries the box, with our billet upper mount bracket on the transmission side. The bracket takes either a GM TH350/TH400 style mount (Energy Suspension 3.1108G poly) or BMW-style bushings.
• Tunnel clearance: remove the OE NVH foam from the tunnel and rotate the cooler adapter block 90 degrees, and the box clears without cutting anything.
• Output flange: the 8HP70 output is 43-spline. The Ram truck flange takes a 1350 U-joint directly (the OEM Dodge 1350 flange, part 68417915A, is the clean solution). Durango and Charger flanges need an adapter.
• Driveshaft: custom single piece with a 1350 joint. The 8HP output flange sits about 25 mm farther back than a 6HP, so measure for length only after the drivetrain is at final ride height on torqued mounts. Our driveshaft guide covers measuring.

Cooling and Fluid

Overheated fluid is the number one thing that puts an 8HP into limp mode, and the factory cooling path doesn't exist in a swap, so you're building the whole cooling circuit from scratch.

• Cooler adapter: a low-profile adapter block replaces the factory cooler connection on the case and gives you 8AN ORB threaded ports. Run PTFE lines from there to the cooler.
• Cooler sizing: a 19 or 25 row cooler in front of the radiator covers street builds; drag and drift cars go 25 to 30 row. A 165 F thermostatic adapter keeps street cars at operating temperature; race cars often run full flow with no thermostat.
• Why not reuse the factory thermostat: the OE thermal bypass valve is restrictive and known to stick, and a stuck valve will cook the transmission. Delete it from the plan.
• Fluid: ZF Lifeguard 8 (ZF part S671 090 312) or a proper equivalent. "Lifetime fill" is marketing; ZF's own service guidance is every 50,000 to 75,000 miles, and a service takes roughly six liters. Fill with the transmission level, and check the level at the specified fluid temperature.
• Mechatronics sleeve: the sealing sleeve at the external connector is a known leak point on used boxes. Fluid wicks into the connector and corrodes the pins, which shows up as TCU dropouts and random faults. It can even brick a flash. Reseal it during the bench service, before the TCU flash.

Shifters

The 8HP is fully shift-by-wire. There's no cable, just CAN messages, which is why shifter choice is flexible:

• Dodge shifter (part 04670717AB): plugs into the harness with our Dodge shifter cable. The natural match for a Dodge donor box.
• BMW F-series GWS shifter: the electronic shifter from F2x/F3x/F8x cars (61319296896) or F0x/F1x cars (61319296904) with the BMW shifter cable. Looks factory in a BMW interior, and our shifter mount sits flush with the OE trim in the E9x console.
• No shifter at all: MaxxECU's shifter emulation runs P/R/N/D from a CAN keypad or plain switches, and a SEQ sequential shifter option exists too.
• Paddles: wire the factory BMW paddles (or any buttons) to MaxxECU GP inputs and enable shift-up / shift-down.

Wiring and the TCU Flash

The factory TCU stays in the transmission and MaxxECU commands it over CAN. Our universal 8HP swap harness handles the physical layer: a DT 6-pin main connector (switched 12V, ignition, ground, CAN H/L), the pre-terminated TCU plug, a 4-pin shifter breakout, and an OBD breakout with a PT-CAN tap for flashing and diagnostics.

Three wiring rules:

• Power-up order matters. The TCU's main power must be live before the key-on wake-up signal, ten seconds or more. Wiring them in parallel is the classic mistake, and the symptom is paddles that randomly stop responding in manual mode.
• Termination: the 8HP TCU has no internal CAN terminating resistor. The bus needs proper 120-ohm termination or you'll chase ghosts.
• Brake switch: the TCU requires a brake pedal input before it will engage any gear. Wire it, don't skip it.

The flash: a one-time reflash of the factory TCU with MaxxECU's custom firmware, done on the bench with the ACDP-2 tool (rent ours or buy it). It's about a 15 minute job once you're set up: read the TCU, send MaxxECU the identification, flash their model-specific files in order. Two warnings that come straight from MaxxECU: the firmware is matched to the exact TCU (check the Bosch part number before buying a donor if you can), and a flashed TCU works only with MaxxECU. It will not run behind a stock Dodge or BMW computer while the MaxxECU firmware is on it.

Tuning and Driving

• Torque table accuracy comes first. The TCU adapts its clutch pressures based on the torque figure the ECU reports. If the tune's torque table is lazy or wrong, shift quality suffers and the adaptations learn garbage.
• Shift cut: the 8HP requires a torque reduction during shifts. MaxxECU handles the request automatically over CAN through its shiftcut settings.
• Adaptation drive: after everything works, the box wants a relearn: fluid around 60 C, light throttle, 1,600 to 3,200 rpm, working through gears 3 to 7. Shifts noticeably smooth out as it learns.
• Drive modes: shift maps are fully adjustable from comfort to race, with kickdown, and shift points anywhere from 1,500 to 9,000 rpm. Set the engine rev limiter about 500 rpm above your shift point.
• Transbrake and launch: built into the firmware, in first or second gear, with a bump feature for staging. With a BMW shifter you can trigger launch by holding the stalk at maximum. Clutchkick and a virtual clutch mode exist for the drift crowd.
• Converter lockup: controlled and reported over CAN, with slip control available.

How Much Power Will It Hold?

ZF rates the Gen 1 8HP70 at 516 lb-ft and the 8HP90 higher still. In the real world, healthy stock 8HP70s commonly live at 600 to 800 lb-ft. Add a Sonnax Zip-Kit and fresh ZF fluid and we've seen 1,000 lb-ft survive on the street. Past that you're into built-unit territory: upgraded clutch packs and billet internals, and serious drag cars upgrade the input shaft, because that's what twists first at four-digit torque.

Two things kill 8HPs at power: heat (see cooling) and bad torque reporting (see tuning). Sort both and these boxes are impressively hard to hurt. If you want more than that, start with an 8HP90 donor instead of building a 70.

Frequently Asked Questions

Guides & Resources

• MaxxECU official 8HP documentation (wiring, flashing, transbrake, every setting)
• Guru Autowerks adapter FAQ (donor identification, starters, converters)
• Transmission section of the LS swap parts list
• ECU comparison: Holley vs MaxxECU vs Haltech
• MaxxECU terminated harness install guide
• Driveshaft basics for E9x swaps
• LSE90 Garage on YouTube, where these builds happen

Ready to 8HP-swap your BMW?

Grab the parts above or hit us up for a quote on your combo.