Launch, trans-brake and bump (drag)
The drag toolbox: hold the car against full power, stage it on a trans-brake, and launch hard. Powerful and capable of breaking parts, set it up deliberately and test in stages. These features need a manual program (see program tuning) and verified torque.
What a trans-brake does
A trans-brake applies two opposing clutch packs at once, locking the gearbox output so the car cannot move while you build engine RPM and boost against it. Release it and the stored energy plus boost launches the car instantly, far harder than brake-torquing a normal automatic. On the 8HP this is done in software through the same clutch solenoids, so it is all in the calibration.
It only works in a manual program (Auto = 0). The trans-brake needs the box to stay in the gear
you command, an automatic schedule would fight it.
Launch / trans-brake settings (firmware V10.75)
Under Launch Settings and the launch tables:
| Setting | What it does |
|---|---|
| T-Brake/ Launch Activation | master enable for the feature. |
| Enable Launch P1..P8 | which programs the launch/trans-brake is armed in. |
| T-Brake Linear/ Launch Press. | the clutch pressure that holds the car (the “brake” force). |
| T-Brake/ Launch Max RPM | RPM ceiling while staged, the launch rev limit you build against. |
| T-Brake/ Launch Torque Reduction | torque cut requested while staged (keeps it controllable). |
| Active T-Brake/Launch in automatic mode | allow it outside pure manual (use with care). |
| Lockup Gear OFF after T-brake/ Launch | drops lockup right after launch so the converter helps off the line. |
After the launch, a second set of tables manages the hit so it hooks instead of shocking the driveline:
- Add Press. after launch: extra clutch pressure once moving.
- Torque Press Correction after launch / RPM Press Correction after launch: trim that added pressure by torque and RPM.
- Add Press. Footbrake OFF: pressure change as you come off the brake.
Activating it
The trans-brake is armed with the footbrake + the upshift input (the inputs are configurable: Footbrake Signal Input, T-Brake/ Launch (footbrake) ON). Hold to stage, build boost to Max RPM, release to launch. On most standalone ECUs the brake is not on CAN, so wire the footbrake
to pin 11 (A7) and verify Footbrake Signal Input Invert matches your signal polarity before relying
on it.
What to expect on the brake
The trans-brake holds by applying the reverse and drive clutches simultaneously. The Zero To 60 N54
ran a 2800 RPM limiter on the brake (T-Brake/ Launch Max RPM), a sane starting point.
How high you can actually stage depends on the converter, not the TCU. BMW diesel converters are tight: they flash to around 4000 RPM on the brake. A laggy 4-cylinder build may only reach ~2500 RPM against the same converter, which may not be enough to spool. If you cannot build boost on the brake, the converter is the limit.
One asymmetry to know: launch control needs an ECU-side launch limiter (otherwise the engine revs free against nothing), but the trans-brake does not, the locked box is the limiter.
TurboLamik’s takeup philosophy runs through all of this: lock the converter early and slip the box clutches, DCT-style. Launch mode works the same way.
Sources: Zero To 60: N54 With Transbrake & Bump, Zero To 60: Thinking About a 8 Speed Swap?
Bump (staging)
“Bump” rolls the car forward a set, tiny distance while still on the trans-brake, how you stage on the beams without releasing. The TCU counts output-shaft pulses (the 8HP output sensor gives 40 pulses per revolution) to move an exact amount:
| Setting | What it does |
|---|---|
| Enable Bump | turn staging on. |
Bump Input (+ Bump Input Invert) | the button that triggers a bump. |
| Bump base clutch pressure | pressure used to nudge the car. |
| Bump Torque pressure correction | trims that pressure by torque. |
| Bump Max distanse, first jump | how far the first bump rolls. |
| Bump Max distanse, next jump | how far each subsequent bump rolls. |
| Bump distanse Clutch press. up | how pressure builds across the bump distance. |
| Enable ramp, pressure reduction | smooths the pressure on/off so it creeps rather than lurches. |
Set the first jump larger to get onto the beams, the next jump small to nudge in. Too much pressure and it lunges through the stage; too little and it will not move.
The distance fields count output-shaft pulses: 40 pulses = one output-shaft revolution. The default first jump is a quarter revolution, and on the Zero To 60 N54 that jumped the car too far; around a tenth of a revolution (4 pulses) felt right. Start small.
Source: Zero To 60: N54 With Transbrake & Bump
Blip (rev-match downshifts)
Not drag-specific, but a sport feature in the same family. On a downshift the TCU asks the engine to blip the throttle so revs match the lower gear, smooth, fast downshifts without a lurch. It needs a throttle path to the engine (CAN or analog), so it does not work on a pure carb setup.
| Setting | What it does |
|---|---|
| Blip Strategy ON | enable rev-match blips. |
| Blip TQ Target (2 RPM × 3) | how much throttle/torque to request for the blip. |
| Min RPM for blip | floor below which it will not blip. |
| Max TPS for blip / Max TQ for Blip | ceilings, do not blip if you are already on the throttle. |
| Clutch slip blip deactivation | cancels the blip if the clutch is slipping. |
A safe bring-up order
- Verify torque and get normal shifts good first. A drag launch on wrong torque damages clutches fast.
- Arm launch only in the program you will race (
Enable Launch Px). - Set a conservative
T-Brake Linear/ Launch Press.and a modestMax RPM. Confirm the car holds, then confirm it releases cleanly, on a safe surface, low boost. - Add
Bumpand tune the jump distances on a flat surface at low pressure. - Raise launch RPM / boost in small steps, checking it hooks (after-launch pressure) rather than spinning or shocking parts.
- Add
Blipfor downshifts once the launch side is dialled.
The trans-brake holds full engine torque through the gearbox and then dumps it into the driveline. It can break clutches, shafts and diffs if set too aggressively. Increase pressure, RPM and boost gradually and inspect your hardware.
Sources: firmware V10.75 XDF (Launch Settings and bump/blip tables as named), the manual’s trans-brake and bump pages. Values vary per gearbox and build, start from the base map for your box at download.turbolamik.eu.