Astra H VXR Sprint

When remapping the Astra H VXR fitted with a K04 (standard) VXR turbo, there are occasions where an uprated actuator is required, usually when aiming for 290-300bhp (or as close to it as you can get) when using the factory K04 KKK turbocharger. The factory actuator has a static break off pressure of around 10psi or so. An uprated, stronger actuator with a static break off pressure of around 12-14psi is needed to overcome the back pressure that builds up in the small exhaust manifold behind the penny valve. The stronger actuator allows for a smoother boost curve and more mid range torque because it can overcome the back pressure and keep the penny valve closed. Without  a stronger actuator the back pressure builds up, and despite the electronic boost control, it becomes too strong for the standard actuator and overcomes it, blowing open the penny valve and causing a loss of mid range boost, at around 3,000 – 3,500 rpm.

For the K06 hybrid turbo that is being used here, which has a billet K06 compressor wheel and a cut back to the turbine (exhaust) wheel, back pressure is much less of an issue due to the cut back reducing the back pressure in the exhaust system and improving the flow through the manifold and down the exhaust. In this instance an actuator with a static break off pressure of around 10psi is suitable. Whilst 10psi is the same break off pressure of a standard VXR actuator the Turbosmart actuator pictured here also has the facility to have the internal springs changed to make it stronger if required, so it seemed an ideal time to try one as the car is due for mapping and final set up. Plus it is a very ‘smart’ looking actuator (excuse the pun!) compared to a standard one.

Turbosmart Actuator

Turbosmart Actuator

Turbosmart Actuator Fitted