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.

Step-by-step launch staging procedure

Select a Manual Driving Program (e.g. Program 6 - Manual Drag, Auto = 0).
Come to a complete stop on the staging line.
Press and firmly hold the footbrake pedal, then pull and hold the Gear UP paddle (or trans-brake button). The TCU will lock opposing clutch packs, arming the trans-brake.
Release the footbrake pedal while continuing to hold the Gear UP paddle.
Floor the accelerator throttle: The engine will build boost against the trans-brake rev limiter (T-Brake/ Launch Max RPM).
Release the Gear UP paddle: The TCU instantly releases the holding clutch and fires the drive clutch, launching the car.

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)

The "Bump" function allows for a controlled, gentle crawl forward into the staging beams while holding full boost on the trans-brake.

When you trigger a bump, the TCU momentarily reduces clamp pressure on the holding clutch pack, allowing the vehicle to roll forward. The TCU reads pulses from the transmission output shaft speed sensor (40 pulses per full output-shaft revolution) and immediately clamps the clutch back into full lock once the preset pulse count is reached.

How to trigger a bump:

Paddle / Button setups: While actively holding the Gear UP paddle/button on the trans-brake, briefly tap the Gear DOWN paddle/button.
BMW F-Series Selector: While holding the trans-brake, press the P (Park) button on the shifter knob to initiate a bump forward.

Setting	What it does
Enable Bump	Master enable switch for bump staging.
Bump Input (+ `Bump Input Invert`)	The physical or CAN channel mapped to the bump trigger.
Bump base clutch pressure	Initial clamp pressure reduction used to allow the car to creep.
Bump Torque pressure correction	Trims release pressure dynamically based on engine torque.
Bump Max distanse, first jump	Target pulse count for the initial bump to cut the first beam.
Bump Max distanse, next jump	Target pulse count for subsequent micro-bumps into the second beam.
Bump distanse Clutch press. up	Controls how rapidly pressure builds across the bump distance.
Enable ramp, pressure reduction	Smooths the pressure ramp on/off to prevent abrupt driveline shock.

The distance fields count output-shaft pulses: 40 pulses = one output-shaft revolution. The default first jump is a quarter revolution (10 pulses). On high-torque builds, around 4–6 pulses (approx. 1/10th revolution) provides a much cleaner, controlled staging roll. Start with conservative pulse counts.

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 modest Max RPM. Confirm the car holds, then confirm it releases cleanly, on a safe surface, low boost.
Add Bump and 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 Blip for 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.