What the function does
A torque converter couples the engine to an automatic transmission through fluid, which means some slip is always present. The lockup clutch removes that slip by joining the two sides mechanically. The Torque Converter function in NSP decides when that clutch engages, and how hard, by driving the converter solenoid with a PWM output.
It has a second job for drag racing: controlling a converter dump valve. Dumping converter pressure reduces how much power reaches the wheels, and it helps an engine come up on the converter on the line before a launch.
When will it lock?
Lockup only happens when every condition you set is met. If any of them stops being true while locked, the converter unlocks. The lock and unlock speeds themselves live in the Lock Point and Unlock Point tables.
| Setting | What it does | Our advice |
|---|---|---|
| Lock Point Variable | The channel compared against the Lock Point table | Driven Wheel Speed for street, circuit and rally cars. Driveshaft RPM for drag cars, since their tires grow and the rolling radius changes |
| Minimum TPS | Below this throttle, no lockup | 0% is the usual choice |
| Maximum TPS | Above this throttle, no lockup | 100% is the usual choice |
| Minimum Coolant Temperature | Keeps lockup off until the engine is warm | Somewhere between 85 and 160 °F (30 to 70 °C) |
| Minimum Gear | No lockup in gears lower than this | Depends on the gearbox; commonly 2nd to 4th |
| Minimum Race Time | No lockup until the race timer passes this value | Useful on drag cars to keep the converter loose off the line |
| Unlock When Braking | Unlocks while the Brake Pedal State is On | We turn it on for street cars; it makes stopping smoother |
| Unlock When Shifting | Lets the converter slip during a gear change | Helps soften shifts |
Minimum Gear needs a working gear channel, so set up gear ratios or other gear detection first. Unlock When Braking needs a brake pedal switch input.
Dyno mode lockup
If the Transmission Control function is enabled, you'll also see Lock When Transmission Control In Dyno Mode. When ticked, the converter locks as soon as dyno mode reaches the dyno gear. That gives a solid link between engine and wheels, so you can hold the engine at low RPM and high load, sites a slipping converter makes very hard to reach. Leave dyno mode (select Neutral or turn dyno mode off in NSP) and lockup goes back to its normal rules.
We recommend having this enabled. Tuning an automatic on a dyno without it is slow and imprecise. More on dyno mode is in Transmission Control.
Output settings
| Setting | What it does | Where to get the value |
|---|---|---|
| PWM Frequency | How fast the lockup solenoid is pulsed | The transmission workshop manual. Around 300 Hz is common, and Haltech transmission base maps already have it set |
| Duty Cycle When Unlocked | The duty sent to the solenoid while unlocked | The workshop manual again. 100% is common, and base maps include it |
| Dump valve Frequency | PWM frequency for the dump valve solenoid | Match the valve you are using |
Locked duty is set separately in the Lock Duty Cycle table, and dump behavior in the dump duty cycle table.
Don't guess the frequency or unlocked duty. They depend on how the transmission's solenoid and valve body are designed, and the wrong values can leave the converter locked when it should be free, or never locking at all. The manual or a Haltech base map is the reliable source.
Troubleshooting
| Symptom | Usually |
|---|---|
| Never locks | One condition not met: coolant too cold, gear channel below Minimum Gear, TPS outside the window, or brake input stuck On |
| Converter state never matches what NSP says it should be | Unlocked duty or PWM frequency wrong for the solenoid, or the output is not assigned |
| Harsh shifts with lockup on | Try Unlock When Shifting |
| Hard to reach low RPM cells on the dyno | Dyno mode lock not enabled |
FAQ
Driven Wheel Speed or Driveshaft RPM?
Street and circuit cars: wheel speed. Drag cars on soft tires: driveshaft RPM, because tire growth makes wheel speed misleading.
Do I need a base map?
It isn't mandatory, but importing Haltech's map for your transmission gives you correct frequency and duty values from the start.
