BMW transmission tuning · ZF 8HP automatic · DKG
xHP Flashtool is the leading mobile TCU tuner for BMW ZF 8HP automatics and DKG dual-clutch gearboxes. Faster shifts, raised torque limits, sharper kickdown, custom launch control. At SamuelTuned, xHP is calibrated as a matched pair with the ECU tune so the gearbox keeps up with the engine, not the other way around.
xHP is the transmission counterpart to the ECU platforms above, it tunes the gearbox, not the engine. Most builds use both: an ECU tune for the engine, an xHP tune for the gearbox.
Buy it now
Custom xHP gearbox (TCU) tune — firmer, faster shifts, raised torque limits, launch control and bespoke shift maps. Shaves tenths off your 0–60, 100–200 and quarter-mile times. Bought on its own or layered on a tuning package.
Road or track. Tell Samuel your goal — quicker 0–60 / 100–200 / ¼-mile drag times, or shift points set up for your circuit — and your settings are dialled to match.
What it is
xHP is a mobile TCU (transmission control unit) flashing platform for BMWs equipped with the ZF 8HP 8-speed automatic, plus the older M-car DKG dual-clutch gearbox. It writes calibration software to the factory transmission controller through the OBD port, no removed TCU, no bench work to start.
Through the xHP mobile app you flash transmission software, manage map slots, switch between calibration profiles and revise behaviour as the build evolves. Available on Android and iOS.
xHP is the only piece of the build that is NOT the engine. The ECU controls power; xHP controls how that power gets to the wheels, shift speed, shift firmness, torque limiters, launch control logic, kickdown response.
The platform
xHP is the app and flashing platform, it connects to the TCU and handles writing, managing and switching transmission maps.
The tune
The tune is the calibration loaded into the gearbox, what controls shift speed, shift firmness, torque limits, launch behaviour and kickdown logic.
xHP makes the workflow possible. The behaviour, smoothness and reliability of the gearbox comes from the quality of the calibration loaded through it, and from how well that calibration is matched to the engine tune sitting next to it.
What it lets you do
Why use xHP Flashtool?
Once an engine is tuned, the TCU becomes the bottleneck. Factory transmission software is calibrated around stock torque, feed it more, and the gearbox protects itself: torque-reducing under load, slipping shifts, dropping into limp, prematurely wearing clutch packs. xHP raises the TCU's torque limits to match the tuned engine output AND sharpens the shift behaviour, so the gearbox finally cooperates with the calibration in the ECU. Without xHP, you are paying for ECU power that the gearbox quietly cancels.
Supported vehicles
Compatibility depends on exact model, engine, ECU type, production date and software version. Some cars need an ECU unlock first, see below.
By far the largest xHP platform. The ZF 8HP 8-speed automatic is fitted to the majority of modern BMWs from F-series onward, including every B58, S58 (the G80 M3 / G82 M4 / G87 M2 run an 8HP variant), and most performance chassis. xHP covers the pre-LCI 8HP45/50/70 and the post-LCI 8HP51/76 generations.
Common models
The S55-era M cars, F80 M3, F82/F83 M4, F87 M2 Competition, M2 CS, run a 7-speed Getrag dual-clutch (BMW's DKG / DCT, not ZF 8HP). xHP supports DKG for raised torque limits, faster shifts and aggressive launch control, the same calibration approach as the 8HP, applied to the dual-clutch hardware.
Common models
The 2020+ Supra 3.0 is a BMW B58 with the ZF 8HP gearbox underneath, so xHP supports it natively. Custom shift calibration matched to whatever ECU tune the Supra is running, Stage 1 through big turbo.
Common models
Hardware
Coming soon to this site, the right adapter, cable and licence for your car, in one place.
xHP delivers via a wired USB OBD adapter, the interface plugs into the OBD port and into your phone (USB-C / Lightning with the appropriate cable). Wired connection makes flashing the TCU more reliable than wireless and avoids the dropouts that can otherwise leave a transmission in an unflashable state.
Required per vehicle. The licence covers TCU flashing, access to the stock OTS files (Stage 1 / 2 / 3) and the workflow that custom calibration sits inside. Custom calibration from SamuelTuned then writes through the same licence.
Inside the platform
Shorter shift duration on supported gears, the gearbox commits to the next ratio sooner, with less smoothing and overlap. Most noticeable on full-throttle upshifts where the stock TCU is heavily de-tuned for refinement.
Stock TCU caps inbound torque from the engine to protect the clutch packs. Once the engine is tuned and producing more torque than stock, those caps cause torque reduction mid-pull and choke off the ECU tune. xHP raises the limits to match the calibrated engine output.
Reduced shift slip, firmer engagement, less drift between gears. Pulls the gearbox towards a sportier, more deliberate character, without the harshness of an uncalibrated "shift-kit" approach.
On supported chassis, xHP rewrites the launch-control logic, launch RPM, line pressure during the launch, clutch handoff. Configured around the actual power level and intended use (drag, roll-race, daily fun).
Sharper, faster kickdown response, the gearbox commits to the lower gear immediately rather than waiting through the factory's deliberate delay.
Sport / Sport+ behaviour rewritten, shift points, throttle mapping, hold-gear logic. Daily comfort modes left alone so the car remains pleasant in normal driving.
Disable auto-upshift at redline in manual mode, the car will bounce the limiter and wait for you to pull the paddle, instead of automatically upshifting on you mid-corner.
Adjusted idle line pressure for cleaner stop-start engagement, reduced creep and crisper take-up when pulling away.
Multiple calibration profiles loaded into the TCU, switchable in-app. Comfort daily map, aggressive weekend map, track-focused map, drag map. No re-flashing each time the context changes.
OTS vs custom
xHP's stock Stage 1 / 2 / 3 files work fine on a near-stock car with a near-stock engine tune. They are not built around the actual torque curve coming out of your engine, the way you drive, or the use case (street vs track vs drag). For an engine that's been properly tuned, an off-the-shelf TCU file is a blunt instrument.
Off-the-shelf
Designed to work across a wide range of cars. Limitations to be aware of:
Built for you
A custom xHP tune is calibrated against the actual torque curve of the engine tune sitting next to it. SamuelTuned tunes ECU and TCU as a matched pair, power delivery and shift behaviour designed to cooperate, not fight. Once it's flashed, revisions come back through the same workflow as the ECU calibration.
Especially useful for
Tune stages
Stage 1
The right starting point on a near-stock car, slightly faster shifts, slightly raised torque limits, marginally sharper response. Daily refinement preserved. Works well on a Stage 1 engine tune.
Stage 2
Where xHP starts to earn its keep. Torque limits raised to match a Stage 2 / ethanol engine tune. Noticeably faster shifts, sharper sport mode, sharper kickdown. The version most tuned daily drivers want.
Stage 3 / Custom
Generic Stage 3 files rarely suit a high-torque build, they assume a typical engine and the launch / shift behaviour gets aggressive enough to wear hardware. Custom calibration is built around the actual ECU map's torque output, the gearbox condition and the intended use.
Remote tuning
Step 01
You'll need the xHP USB OBD interface, the wired adapter that connects your phone to the TCU. Available directly from xHP and from this site.
Step 02
Install xHP on Android or iOS, register your vehicle and activate the licence covering your chassis (8HP variant or DKG).
Step 03
xHP is calibrated against the torque curve coming out of the ECU. The engine tune (Bootmod3, MHD or MG Flasher) goes in first; the matched TCU calibration is built around it.
Step 04
Samuel issues your first xHP calibration file. You flash it through the app over the wired OBD adapter. Wired connection is important, a wireless dropout mid-TCU-flash is exactly the failure mode the cable is there to prevent.
Step 05
Daily, launch, kickdown, manual mode, sport mode, whatever the calibration targets, you drive the car through it so the behaviour can be observed.
Step 06
Samuel adjusts shift speed, torque limits, launch RPM and any specific behaviours that need refinement. You re-flash.
Step 07
Once the gearbox cooperates with the engine tune across the entire driving envelope, the calibration is finalised. Map slots are loaded for any context-switching you want.
Before we start
Getting these right makes the tune faster, cleaner and safer.
FAQ
Anything else, message Samuel directly, every xHP Flashtool build is different.
A mobile transmission flashing and tuning platform for BMW ZF 8HP automatics and the F-series M-car DKG dual-clutch. xHP writes calibration software to the factory transmission control unit (TCU), not the engine ECU.
In almost every case, yes. The stock TCU is calibrated around stock torque; once the engine produces more torque than that, the TCU caps power back to protect the clutch packs, and the ECU tune fights the gearbox the whole way up. xHP raises the TCU torque limits so the engine tune actually gets to deliver.
Yes, those cars run an 8HP variant and are fully supported. xHP is essentially mandatory on those chassis once the engine has been tuned.
Yes, xHP is fully remote-capable. SamuelTuned issues calibration files, you flash through the app, you drive, datalogs come back, files get revised. No workshop visit required.
Yes, xHP supports both iOS and Android via the wired USB OBD adapter and the matching phone cable for your device.
Yes, xHP works on a stock engine. The benefit is smaller (the stock TCU is reasonably matched to stock torque), but Stage 1 still gives noticeably faster, sharper shifts. Most customers come to xHP after the ECU tune is in place.
On a custom-tuned engine, yes, significantly. Stock xHP files are generic, calibrated for a typical torque curve. Custom xHP is matched to the actual ECU map running on your car, your gearbox condition, your driving style and your use case. On a stock-engine car, the off-the-shelf files are usually enough.
Yes, when calibrated properly. The risk comes from generic, overly-aggressive settings on a high-torque build (launch RPM too high, line pressure too aggressive, torque limits raised beyond what the clutch can take). Custom calibration is built around the actual gearbox and the actual engine, not a blanket setting.
Keep exploring
Engines
xHP pairs with an engine tune. See every BMW engine we calibrate.
Learn morePlatform
Pair your ZF 8HP gearbox tune with a bootmod3 engine map.
Learn morePlatform
Run xHP alongside an MHD engine calibration.
Learn moreCompare
How the BMW tuning platforms compare.
Learn moreReady to start
If you've already tuned the engine, the gearbox is the bottleneck. xHP fixes that. Custom calibration matched to the ECU tune, delivered remotely, anywhere in the world.
