Quote:

BUT............................
At 60mph you're using about 35 horsepower and no matter what engine is on the front, the torque converter clutch only has to transmit the torque to make that horsepower at the cruise rpm.



That assessment is completely correct at steady-state. And your trans could be a grenade with the pin pulled. For many things in life it's not about what's going on -- but rather what happens next.

When you open the throttle the engine torque will increase, and you’ll need to have enough LU pressure to keep that clutch clamped. And in OD the vehicle load/resistance is actually higher than in lower gears, so the normal human instinct will be to push more throttle.

how the OEMs do it
An OEM designed system will know what that new torque is (a calculation from the engine ECU, also validated by lots of testing) and adjust pressure or drop LU and/or OD. Things are designed and calibrated from clutch area, coeff of friction, pressure, temperature, etc, + a safety factor. All of this is highly reviewed/calculated and then validated by *lots* of testing. Wanna have fun? Ask your trans expert the coefficient of friction of OEM paper vs the Red friction, and see what his response is.

but I’m aftermarket?
But in an aftermarket application you might only have a TPS signal (with EFI, or if a TPS has been piggybacked onto a carb for such a purpose). You’d need to make sure your module will put enough pressure on the LU clutch when that happens. Even then you wouldn’t know how much pressure would be required, so maybe you’d just make it the max for anything above say 50% throttle? But how would you know if 50% was the right setting, or if max pressure was enough? Who wants to toast their LU clutch to validate their assumptions?

Sheesh, dude, I’ll just do this then.
So let’s say you play it safe and go with 30% for max pressure.

Well, another thing is :
If your rpm (trans input rpm) is low enough due to being in OD the pump flow could be low (via pump sizing and/or electronically-controlled pressure bleedoff). Modern transmissions keep pump flow just above the minimum for any given condition, as pumping oil costs hp and fuel, and a transmission is known to be a good place to minimize fuel usage. So even if you tell your aftermarket controller to command max pressure, you might not get it -- and you wouldn’t know, either. Oh, you might know if you got slippage, and it would be easy to misdiagnose the reason and put an incorrect/inadequate fix in place, thinking you fixed it, and maybe get a worse slip next time (or in a different clutch).


Also, just because you can easily change behavior via solenoids, you still have the mechanical characteristics of valve bores and valves/springs, some of which balance/feed off each other. For any pressure you increase for one clutch, you may risk decreasing pressure to a different one, or altering cooler flow (which is also your lube circuit). I would think this would be an area where many transmission modifiers would get themselves out on a limb and have warranty issues until they figured the limits of the hardware.

If you’re still reading all this
I spent many an hour looking at real-time data traces of transmission testing, as controlled by an ECU or a module to manually trigger solenoids, and have seen more than a few puffs of smoke come out of a dipstick tube for a variety of reasons. I had the luxury of doing an autopsy afterward, to look at data (secret ECU data and also instrumented transmission data) that very few hotrodders will have access to (or interest in). I also had to be trained in how to interpret that data, as it was easy to incorrectly identify ‘the smoking gun’. Specific to this discussion - I’ve seen pressures be commanded yet not be obtained -- and not always for the same reason.


So back to the grenade –
You can program your controller with the best intentions, and pussyfoot when in OD/LU, but wouldn’t you always wonder if you pushed the throttle too hard at highway speed if you’d hit the limit?

As hotrodders we're conditioned that things break from being pushed too hard, but IMHO an electronically-controlled transmission can be disabled under simple driving conditions if it's modified incorrectly.

what I'd do:
If I had a high-torque engine and LU, I'd get a converter with the best friction material I could afford, and maybe boost LU pressure a little. Then I'd drive around cautiously and make sure my module drops LU and OD very readily with increase in throttle and drops them in the same pattern as the OEM did (simultaneously, or one before the other) and then I'd tweak it to until annnoyng. Then I'd drive some more and raise the TPS threshold to where I could drive it without cycling things too much with my foot. then maybe raise the LU pressure a few percent. And then nobody would drive that car but me unless it was an emergency...

Unless you're *really* intimate with a particular transmission, follow the factory footsteps as much as possible.