Project GD STI: Making More Power with Cobb Tuning and Precision Turbo Part 2!


Now the mechanical part of our Cobb Flex Fuel conversion is done!

To do the ECU side of the flex fuel conversion, we upgraded our original Acess Port to the latest V3 version from Cobb. The V3 has the additional speed and monitoring features we need. 

To fix our lack of boost issue, we switched our stock two port boost solenoid with Cobb's 3 port unit. This will give us better boost control.

The stock 2 port boost control solenoid works by controlling the boost pressure, feeding the wastegate actuator by bleeding pressure off to the actuator. The 3 port uses a different control logic and vacuum hose routing in order to block the high pressure air going to the actuator diaphragm.

This makes for more aggressive control of the wastegate, as the wastegate actuator can see zero boost pressure while the turbo is spooling. It also permits a higher maximum boost, since it is possible to completely block the actuator reference signal with the solenoid. 


We also got rid of our 15 PSI actuator and switched to a Precision Turbo 20 PSI actuator. 

One of the reasons why we needed such a stiff actuator is that the Precision Turbo has a large internal wastegate flapper valve to avoid boost creep. As you can see here, it is quite a bit larger than the stock valve. The large area of the valve requires a lot more control pressure to keep it from blowing open, as we found out. 

The Cobb 3 port boost control solenoid is a direct bolt in replacement for the stock 2 port part. 


Leave a Reply

Your email address will not be published. Required fields are marked *