Bazil_SW

iTrader: (4)

Hi All.

I'm having a boost control issue that I hope someone can shed some light on.

History

I run a 2.5 forged build with TD05 20G turbo. The stock Hawk STi ECU does not have per gear boost control, and as such I run a 2 stage (switchable) boost controller that at it's heart uses two Dawes MK1 MBCs, set to high and low boost.

High Boost = target 15psi for gears 1-->4
Low Bost = target 12 psi for gears 5 and 6

this is intended to prevent the shuddering which occurs on high torque 2.5s at ~3-3.5k rpm when in 5th and 6th gears - I've discussed this previously and it's talked about extensively on the US Legacy forums.

Setup

The TD05 20G I bought came as std with a 12-14PSI wastegate actuator. I found this was too high and I could not control boost at any setting. I bought a Mamba adjustable W/G actuator and fitted the 8PSI spring. Hose lengths are kept as short a physically possible.

The problem


With any of the set ups below I'm experiencing pretty rubbish boost control that can definitely be felt when driving.

1) Just the dawes
2) Dawes + bleed type MBC after dawes
3) bleed type MBD only

The graph below is pretty typical, you can see a spike and dip that takes a lot of RPM to recover. The graphs looks pretty much the same for the above 3 arrangements

My conclusions so far


Because all 3 arrangements of boost controller are giving similar results, I'm concluding it's likely the W/G actuator that's at fault here, perhaps even experiencing a sticktion affect when opening?

Does anyone have any thoughts on this?

Cheers!