adjustment of converter lock

[tmsbandman]

I was playing with my custom 87 performance tune, and adjusted the converter lock to it's lowest settings (just to see how it responds.) Gryphon SAYS my AVG ECON is better, and I'm OK with it from a performance standpoint. But-Is there some other trade-0ff? I understand engines decently well, but not trannies. This adjustment causes the converter to lock at a lower speed, right? What is the benefit/risk of adjusting the converter lock points on decel (4-3, 3-2, 2-1.)

Thanks,
Rick

[Longshot270]

Nothing bad will happen.

By lowering the unlock points, you effectively engine brake a little bit longer when you let off the gas pedal. If you raise it, you can free roll more after letting off. Both directions of modification have useful applications.

I do recommend that you keep the lock and unlock points corresponding though. When they are different, it often causes confusion in low throttle and cruise control applications.

[tmsbandman]

Thanks. I will set them the same. From what you describe, it seems like a HIGHER unlock point would be more fuel efficient. Wouldn't coasting be better (econ wise) than engine braking? I think the Gryphon manual says higher settings give better performance,and lower give better economy.

[Longshot270]

You and the manual are both correct.

On acceleration, where the manual is focused, lower lock points means the RPMs make their biggest drop sooner, reducing fuel usage but you take a hit on performance. Higher lock points keep the engine in the higher RPMs where more power is generated.

On deceleration, this is all opposite. Lower lock points keep the TC locked longer. This gives a better control of speed and improved braking (both engine braking, and forced higher RPMs helping the brake booster), a nice performance aspect useful in fooling around and towing. Higher lock points, as you mentioned, will allow the engine to drop to a lower RPM while decelerating.

Now before you jump up and program the max and mins, here is an important point. You have to keep the two points the same because every time the throttle is applied the TC would be locking, then if you let off it would unlock. The result would be unnecessary transmission work and an unsettling ride if you were to use cruise control.

Here is a graph I made a long time ago to show someone how the engine reacted to TC lock points being changed. Pictures are worth a thousand words.

[tmsbandman]

Awesome info. Thank you. So-just to make sure I understand. The IDEAL fuel efficiency would be low lock points on accel and high lock points on decel?

But-I understand that I need to keep them the same. Just seeing if I'm understanding the function properly.

[Longshot270]

Yes, I'd imagine some of the modern fuel efficient cars are using this strategy...or at least I hope. If you've ever been driving a manual vehicle and noticed your gas was on E with nothing but empty road ahead, chances are you used that method.