5EAT Tuning and how not to end up with a farked gearbox...
Posted: Mon Apr 01, 2013 11:38 pmSo we all know from the US forums that the 5EAT gearbox is not quite as strong as it should be, with boxes slipping on spool and resulting the transmission grabbing after peak engine torque occurs. Being an electronic device, it can function quite well when fed the right signals though!
The Auto Transmission is controlled by the engine ECU, with the transmission computer being fed the right signals from the accelerator pedal via a Requested Torque value
This is the Target Boost Table which is probably the most crucial element
Factory on the Left, middle shows a Tuned car and the right hand side is one of mine
The major difference you will notice is that the middle graph has essentially added boost from 2400rpm to 5200rpm in the 310+ Requested Torque Columns which makes boost come on both earlier on the accelerator pedal movement but also at a low rpm, with the tune then having a smaller boost increase above 5200rpm. The fueling and timing was then tuned to allow the engine to make more engine torque... unfortunately, the Transmission has no way of knowing your making more... so the result is that above 2400rpm, the transmission is not applying enough line pressure to account for a specific engine torque increase so keeps the same line pressure, not to mention leaner mixtures means that your making more torque so it allows the transmission to slip. Once peak torque occurs though, the transmission is able to take the stored energy and bump up the peak power output as the transmission catches up.
So how is the 5EAT 'fixed' if you want more power... you will notice at 2400rpm and 310 Requested Torque, the stock tune asks for 11.2psi, the dyno tuned car asks for 13.79psi but in my tune I am asking for 6.5psi boost
Reasoning is, that with optimised fuel and timing, the engine made similar torque to stock so epects the equivalent transmission line pressure despite less boost. I actually have 20% more line pressure being request with a value of 420 to get similar boost values, which is where the transmission is able to maintain gear ratio lock up 
To put this into perspective, the Automatic MY10+ Liberty GT has a Target Boost 350 column requesting a peak of 12.38psi boost but the accelerator pedal asks for a value of 390 to let the transmission lock up better(Subaru had learnt a thing or two by then although it is not perfect!)
The give away signs of transmission slip(and pending gearbox rebuild) is engine rpm being higher at a specific road speed than it should be. If you are doing 2000rpm in 3rd at 50kph, 3000rpm at 75kph, 4000rpm at 100kph and 6000rpm at 150kph, then the car should be relatively issue free. With a turbo upgrade, the transmission slip is usually more obvious and results in higher peak power figures after peak torque but also higher rpm values at low road speeds than a stock turbo.
Dyno Dynamics are by far the worst offender, as they use either engine rpm or roller speed, with no overlay of the two values to ensure there is no transmission slip as per this article: http://www.airboytuning.com/archives/138 which also shows how derived dyno engine torque is artificially bumped up on any dyno if there is transmission slip.
I know of 3 tuned 5EAT's that had/needed rebuilds within a year of the tune. One was instantly aware of the issue when he knew he could tow a small camper caravan pre-tune at low rpm sitting on 80kph but was sitting above 4000rpm in 4th gear post-tune the weekend after the tune... after the gearbox was replaced, I was asked to retune the car and the difference was immediate It made less power on the same dyno but with more low rpm torque reaching the wheels so was consistently a full second quicker to 100kph than its previous tune. This also allows the gearbox to shift smoother but also kickdown into the right gear as it knows how much torque to expect from the car
Of course, this also applies to the H6 5EAT and even the 2.5L 4EAT's, albeit the 4EAT is a bit more resilient! I am currently retuning a Raptor Supercharged 4EAT 2.5i Liberty which only has a DBW fix applied... no more transmission slip and we even raised the transmission shift point!
This can also be shown in Mark's Veloci build thread, where just the initial DBW settings provided to Mark to sample the difference made a massive improvement to driveability and transmission line pressure lockup resulting in firmer, positive shifts by having more Requested Torque at lower throttle angles.
The Auto Transmission is controlled by the engine ECU, with the transmission computer being fed the right signals from the accelerator pedal via a Requested Torque value
This is the Target Boost Table which is probably the most crucial element
- 5EAT_Target_Boost.png (86.34 KiB) Viewed 32888 times
Factory on the Left, middle shows a Tuned car and the right hand side is one of mine
The major difference you will notice is that the middle graph has essentially added boost from 2400rpm to 5200rpm in the 310+ Requested Torque Columns which makes boost come on both earlier on the accelerator pedal movement but also at a low rpm, with the tune then having a smaller boost increase above 5200rpm. The fueling and timing was then tuned to allow the engine to make more engine torque... unfortunately, the Transmission has no way of knowing your making more... so the result is that above 2400rpm, the transmission is not applying enough line pressure to account for a specific engine torque increase so keeps the same line pressure, not to mention leaner mixtures means that your making more torque so it allows the transmission to slip. Once peak torque occurs though, the transmission is able to take the stored energy and bump up the peak power output as the transmission catches up.
So how is the 5EAT 'fixed' if you want more power... you will notice at 2400rpm and 310 Requested Torque, the stock tune asks for 11.2psi, the dyno tuned car asks for 13.79psi but in my tune I am asking for 6.5psi boost
Reasoning is, that with optimised fuel and timing, the engine made similar torque to stock so epects the equivalent transmission line pressure despite less boost. I actually have 20% more line pressure being request with a value of 420 to get similar boost values, which is where the transmission is able to maintain gear ratio lock up To put this into perspective, the Automatic MY10+ Liberty GT has a Target Boost 350 column requesting a peak of 12.38psi boost but the accelerator pedal asks for a value of 390 to let the transmission lock up better(Subaru had learnt a thing or two by then although it is not perfect!)
The give away signs of transmission slip(and pending gearbox rebuild) is engine rpm being higher at a specific road speed than it should be. If you are doing 2000rpm in 3rd at 50kph, 3000rpm at 75kph, 4000rpm at 100kph and 6000rpm at 150kph, then the car should be relatively issue free. With a turbo upgrade, the transmission slip is usually more obvious and results in higher peak power figures after peak torque but also higher rpm values at low road speeds than a stock turbo.
Dyno Dynamics are by far the worst offender, as they use either engine rpm or roller speed, with no overlay of the two values to ensure there is no transmission slip as per this article: http://www.airboytuning.com/archives/138 which also shows how derived dyno engine torque is artificially bumped up on any dyno if there is transmission slip.
I know of 3 tuned 5EAT's that had/needed rebuilds within a year of the tune. One was instantly aware of the issue when he knew he could tow a small camper caravan pre-tune at low rpm sitting on 80kph but was sitting above 4000rpm in 4th gear post-tune the weekend after the tune... after the gearbox was replaced, I was asked to retune the car and the difference was immediate
It made less power on the same dyno but with more low rpm torque reaching the wheels so was consistently a full second quicker to 100kph than its previous tune. This also allows the gearbox to shift smoother but also kickdown into the right gear as it knows how much torque to expect from the car Of course, this also applies to the H6 5EAT and even the 2.5L 4EAT's, albeit the 4EAT is a bit more resilient! I am currently retuning a Raptor Supercharged 4EAT 2.5i Liberty which only has a DBW fix applied... no more transmission slip and we even raised the transmission shift point!
This can also be shown in Mark's Veloci build thread, where just the initial DBW settings provided to Mark to sample the difference made a massive improvement to driveability and transmission line pressure lockup resulting in firmer, positive shifts by having more Requested Torque at lower throttle angles.
