Mopar Muscle Association UK

Understand Ivor, but at 2000rpm it is making only 100bhp and 300ft/lbs torque - not exactly stump pulling performance.

Then the motor starts to come "on song" at 4000rpm, & it eventually produces 630bhp & 500ft/lbs torque.

This is why you need the slippy convertor. A Loose convertor also makes it more driveable on the street, cos you are not "Jonny mental" all the time. With the roller cam it is like a switch........

May be getting switch pitch and lockup convertors confused.

Buick put switch pitch convertors in their cars back in the mid sixties. Use an electrical switch to actuate a hydraulic plunger that alters the angle of the stator. Allows the TC to 'stall' at two different speeds. Usually high stall to get moving then lower stall when on the move. Using the manual over-ride can be fun. Ran around in a deuce and a quarter that really, really could launch on street tyres with a switch pitch using an extra floor dip swicth as the trigger.

Later more modern TC's actually lock the two halves of the convertor together to give no slippage. The GN had one. It locked up automatically in fourth, dependant on a number of factors (speed, load, revs, gear selection) and the ECM commanded the lockup. You could notice the revs drop. A TC lockup test was to be cruising at, say, 60mph and just kiss the brake pedal with your foot. The TC would unlock, revs would rise approx 500rpm, then almost immediately drop back again as it relocked up.

Luckily, with the Buick's old ECM, on the ALDL (the diagnostic connector) if you shorted two pins you could manually lock up the convertor. I used this during racing, when, after the box had automatically changed to third you flicked a switch and locked the convertor. The locked convertor was good for 2-3mph in the quarter mile. Timing of actuation was very hit and miss. The load factor in third gear is huge (whereas it is very low in first, slightly higher in second). Locking the convertor too early could pull too many revs out of the engine, which the little V6, especially in such a mild state of stock tune as mine, could struggle to pull you back out of.

The proceedure after passing the timing lights was knock the auto into fourth and then disengage the lockup. If you leave it manually locked up and slow down and let the car downshift automatically, you get to the same situation as a manual car in too high a gear and too low a speed. Not very happy. This is where the TC slippage takes over.

Not sure if that helps with lockups.

I have always thought loose or tight has nothing to do with stall, you can have 2 convertors that stall the same but the tighter one will launch soft and have very little slippage at the end of the track.
The turbo action J, is a tight convertor, designed to hook the A body Hemi cars, at a time when tyre technology was limited.
Mick