Nissan GT-R Accesstuner Updates – 20+ Bar Clutch Pressure

GTR TCM

The COBB Accesstuner Software now has the functionality to increase clutch pressure!  This can prevent clutch slip and premature wear even on vehicles producing higher amounts of torque.

The dual clutch (GR6) transmission in the R35 GTR utilizes two multi-disc clutch packs for power transfer to each of the gear shafts.  One gear shaft drives even gears while the other drives the odd.  The clutches alternate engagement to select which shaft to send power through allowing the non-powered shaft to select a new gear.  This alternating engagement allows the transmission to very quickly and sequentially upshift and downshift by routing power from one shaft to the next as gear engagement is incremented or decremented.

A limitation of this system is that a clutch pack must couple all engine torque to its gear shaft.  This torque can sometimes exceed the capacity of the clutch for a given lockup pressure.  The clutch pressure is TCM controlled by a hydroelectric solenoid.  Low pressures and ramp rates allow for comfortable engagement while high pressures and ramp rates maintain low slip angles at high load.

COBB’s GTRs are both USDM 2012+ which have revised stock seals compared to CBA (09-11 USDM).  Anything over stock 16.5 has high potential for problems on stock CBA seals.  At 17 bar or greater, it’s only a matter of time before they fail.  With that in mind, for those with CBA cars, this feature should only be used if you have upgraded transmission seals.

As for the DBA cars, although typical maximum clutch pressure for a stock TCM calibration is around 16.5bar, it has been discovered that 20bar is a reasonable increase in pressure.  This allows for greater clamping force while maintaining mechanical integrity of the transmission seals and otherwise.

This functionality is compatible with Gen 1 and Gen2 TCM ROMs including:

  • Gen 1 TCM
    • Nissan GT-R TCM LC4 KB51A
    • Nissan GT-R TCM LC4 KB51B
    • Nissan GT-R TCM LC5 38B0A
    • Nissan GT-R TCM LC5 38B0B
    • Nissan GT-R TCM LC5 KJ10A
    • Nissan GT-R TCM LC5 KJ10B
  • Gen 2 TCM
    • Nissan GT-R TCM Gen2. LC1 62B1A
    • Nissan GT-R TCM Gen2. LC1 62B1B
    • Nissan GT-R TCM Gen2. LC2 NISMO 89S0B
    • Nissan GT-R TCM Gen2. LC3 80B0A
    • Nissan GT-R TCM Gen2. LC3 80B0B
    • Nissan GT-R TCM Gen2. LC4 6AV0A

This feature is available via a custom tune with the Accesstuner Software for users with a TCM flashing capable Accessport (NIS-006 or NIS-008).


AVAILABLE ADJUSTMENTS

20bar

 

CLUTCH A & B SOLENOID CURRENT (MAX)

Two clutch solenoid current maximums exist in the software.  The base value is typically 1.5 amps.  Increasing the current value to around 1.8 amps will often achieve around 20bar of pressure.  Raising the current values alone is enough to increase the clutch pressure.

CLUTCH A/B TARGET PRESSURE

When increasing the clutch pressure you’ll need to increase this value in order to avoid throwing a clutch pressure DTC.

 

The amount of pressure increased per current increase can and will vary based on the age of the transmission.  Additionally built transmissions with upgraded clutches or solenoids will respond differently from a standard transmission in terms of how much amperage is required to achieve your pressure goals.  No matter the transmission’s condition, we recommend small changes starting at a known safe value for your setup rather than skipping immediately to a higher value, as this could potentially cause damage to the existing seals.  It should also be noted that it is possible to achieve greater pressures with higher solenoid current settings.  Be careful when raising the setting too great as you can exceed the capacity of the DBA seals above 20 bar.

Additional Updates

Additional features using the COBB CAN Gateway have also been added to the Accesstuner Software for end users.  These include:

 


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