4l65e shift pressures and steady state pressures

[Robert67]

Hello folks,We have restored a 67 malibu with a GM crate 350 HO and 4l65e transmission. The transmission came with tuning for drag racing but in fact this is a street car. For whatever reason GM can’t seem to get me tuning for street application so I am looking for help. I have already modified the shift points so that the car is drivable but I don’t know where to set the steady state pressures. I have changed the shift point curves in the graph in the GM TCU software to my liking but I have no idea where to set the steady state pressure curves. The documentation is no help. I can’t even find information on the web about the steady state pressures. The reason I’m pursuing this is because the transmission runs a little hot at over 210 degrees on a 55 degree fall day. The shifts are still firm and fast so I’m wondering if the steady state pressures are wrong for my shift points. Can someone explain the difference between these two pressures and help me adjust the steady state pressures to appropriate values? The drag tuning had the shift and the steady state pressure curves almost identical.

[Robert67]

Anybody?

[andrewb70]

Are you actually measuring the pressure? With the Holley automatic control, the pressure is generally set as a % duty cycle. The higher the duty cycle, the less pressure, zero duty cycle is full line pressure.

Andrew

[Robert67]

Not physically measuring yet. Just trying to get a starting point for the pressure valve current vs throttle position graph curves. The only chart I have for this is the one for the drag racing tune that I was given by GM. I’m attaching the chart194236

[Robert67]

Trying to figure out if I should pair this same setup with my custom street shift pressure tune or if i need to modify these steady state pressures too.

[Robert67]

To simplify the question, should the steady state pressures be the same regardless of whether the shift pressures are racing hard or street soft?

[andrewb70]

To simplify the question, should the steady state pressures be the same regardless of whether the shift pressures are racing hard or street soft?

With Holley EFI, the pressure is based strictly by TPS. Generally less pressure under part throttle and then increasing with TPS.

[Robert67]

I understand that but I did not get a tune for the street from GM and they can’t seem to get me one so I’m having to create one from scratch. I don’t know where to set the pressure curves for the steady state pressure. I’m asking if I need to soften them up or not? The image above is what they sent with the drag race tune. I modified the shifting pressure curves to suite me for street driving. Just looking for help with the steady state pressure curves. The car drives fine with the steady state values in the chart above but runs the trans a little hot. I assume pumping the pressure up and down generates heat so I was wondering if these steady state pressures are higher than necessary for a street tune since these above are for a drag race tune. Should I soften them up a bit or leave them alone?

[Robert67]

If I knew what the actual pressure should be at minimum throttle and at maximum throttle for a street tune for each gear I could extrapolate a linear curve between the two points for each. That would probably get me close to right.

[andrewb70]

I can't answer your questions directly, because I don't know the answers. However, generally speaking, reducing pressure tends to increase hear, because there is more slip during shifts.

Andrew

[Robert67]

Understood. It’s a shame that a major piece of equipment at $3500+ does not come with proper documentation.

[Robert67]

After installing US Shift's software and looking at their ready to use, out of the box tunes I was able to deduce that the steady state pressures are nearly identical for all of their tunes for a given transmission. So I will assume that the steady state pressure curves that came with my race tune from GM are satisfactory for my custom street tune.
Thanks for all the feedback/help.