Rev Hang <-> Clutch Slip - EvoXForums.com - Mitsubishi Lancer Evolution X Forums
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SST Post all topics about the SST transmission here.

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Old 11-27-2018, 03:35 PM   #1
Dr. Jekyll
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Rev Hang <-> Clutch Slip

Hoping one of you SST gurus can help me out here.

Background:
I have a 2011 MR with about 48k miles. The car has been babied all of its life and is properly maintained. Mods are, effectively, the Cobb stage 4 package, plus e85 and equal length exhaust headers.

Problem:
Since the stage 4 upgrade, the SST simply won't give me the same crisp, quick shifts. Using the stock SST maps, I get nasty rev hangs starting around 4000 RPM.

Fix attempt 0:
I flushed the SST fluid and replaced it with good ol' Diaqueeen SSTF1. I also replaced the filter. Although the old fluid was dark, there was nothing unusual about it (no metal flakes or fibers from the clutches were present). This did not have any effect on shifting, whatsoever.

Fix attempt 1:
I drastically lowered the Clutch Pressure Ramp Up tables A-C. This did get rid of the rev hang (yay!). However, lowering these tables introduced a lot of clutch slip (I'm seeing slip values over 200 on both even and odd clutches during spool up @ 2500-4000 rpm and 90-140 load, especially at partial throttle). If I increase the CPRU tables, then the slippage goes way down...but then the rev hang comes back.

Fix attempt 2:
I was using the Cobb AccessPort/AccessTuner and suspected that, perhaps, Cobb was overwriting some important SST table. I flashed the car back to stock and then loaded a fresh ROM onto the car using Tactrix/EcuFlash. I then updated the necessary tables and...nothing. No change. The car still rev hangs with stock CPRU values.

Fix attempt 3:
I read in one of the SST ECU table development threads that the "Clutch Pressure - Unknown" table has a dramatic effect on shifting behavior. I fooled around with that table, even taking it to its lowest and highest possible values. That did nothing. Apparently that table only has any effect on 2008-2010 vehicles. On my 2011 car (ROM 56900009), it doesn't do anything.

Fix attempt 4:
I tried inflating the load values by 20% by increasing all MAP and MAF calibration tables and then correcting the fueling with a reduction to "Calibration Fuel Map" (aka "Engine Volumetric Efficiency"). It's unclear whether this did anything. I still noticed some slip but the car kept throwing DTC's and reverting to some other baseline engine map. I'm sure I could have quieted the DTC's by making changes to some phantom airflow check table, but I got the sense that this was a fool's errand.

Question:
Is there a table(s) buried withing the 56900009 ROM that effects de-clutching pressure like the "Clutch Pressure - Unknown" table did for the 2008-2010 cars? Or is there another way of getting clutch pressures up in these "slippy" spots while keeping the CPRU tables low? Does anyone have any other ideas for eliminating rev hangs without introducing excessive slip?

Thank you, in advance!
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Old 11-27-2018, 06:11 PM   #2
kozmic27
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1. The ecu needs to be properly adjusted.
2. It is possible to exceed the clutch capacity with the stock turbo.
3. leaving the transmission related tables stock when you increase the output of the car will eventually damage the clutch.


As for crisp shifts, if you at the edge of capacity, that isn't going to happen. What clutch pressure are you logging, and what mode are you doing having issues in, and who tuned your car?
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Old 11-30-2018, 10:44 PM   #3
Dr. Jekyll
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Hey Kozmik,

Thanks for replying. I appreciate it.
  1. Yes, that's precisely what I'm attempting to do.
  2. I'm aware that it is. I'm running pretty mild timing and boost during spool-up in an effort to prevent the cooking of clutches.
  3. I've updated all of the relevant tables to support my current power curve. The car runs wonderfully with the exception of the SST rev hang-or-slip issue.

The car is tuned by me. I'm comfortable with everything besides the SST (haven't worked with one before). I'm very happy to share my tune with you and the community if that will help shed some light on the issue. In order to keep from damaging clutches while I figure this out, I'm keeping it below 50% throttle (for the most part) and have turned boost down to ~20psi max.

I'm attaching a log. It shows a part-throttle pull from 2nd - 4th in Sport mode. As you can see, there is a lot of slip in 2nd during spool up, but once load stabilizes a bit in 3rd and 4th, clutch slip drops to about 10 and stays relatively consistent. Because slip only seems bad as load ramps up, that leads me to believe that my current CPRU tables are too low. The pressure in the "acceptable" regions hover around 200psi (7000*2*0.0145). From what I've read, I think that should be pretty normal for that load and rpm.

I appreciate your thoughts and feedback.
Attached Files
File Type: csv Eva Stage4+ E85 v4.61_181130131144_trimmed.csv (7.4 KB, 23 views)
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