TORQUE CONVERTER - the root of all evil?
A lot of xHP customers go for our tunes, because they want to get rid of the sluggish feeling, automatic transmissions often have built in. Especially on Diesel applications, the factory setups slip a lot in the first 3 gears, which makes the car feel like it was pulled by an invisible "rubber-band" instead of a proper engine.
While this ensures a very comfy ride on low loads, it turns into the opposite with anything above 25% throttle. The transmission starts to slip a lot and lets the engine rev unnecessarily. Instead of proper acceleration, you get bad mileage and heat in the transmissions oil. The Lock-Up clutch is opened in that situation, so all torque only gets transfered through the torque converters oil, but not through a solid connection.
But the Torque Converter, combined with the Lock-Up Clutch can do some pretty awesome things, that aren't really recognized. With the right setup, it can combine the best of both worlds. A direct connection between engine and transmission and precisely controlled slip to aid acceleration.
The Datazap Log below shows a full throttle acceleration from 80 - 120 km/h (50 - 75 mph) in 5th Gear in a BMW 330d with N57 Diesel Engine. For the tech-savy, note the difference between Engine-RPM and Turbine-RPM. As soon as you get on the throttle the Torque Converter Clutch starts to control slip, to help the 330d's Turbo spool more quickly and therefore accelerate faster.
We did the measurement and the difference between "No Slip" and "Controlled Slip" is 0.4 Seconds from 80 - 120 km/h. Your car actually gains nearly half a second from 80 - 120 km/h with a proper Torque Converter Setup.
Of course this can induce extended wear on the Clutch, but the smart ZF6HP uses fine tuned formulas to calculate whats allowed and whats not allowed. The Slip function goes to sleep once a certain temperature in the clutch material is reached. Until that the majority of wear is kept in check through the transmissions oil.
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