Long, Low and Slow
Join Date: Nov 2010
Location: United Kingdom
County: West Midlands
The system works by creating a partial vacuum throughout the Boost Control System(BCS), this is enough to move the turbo actuator closing the vanes inside the turbo to increase the amount of boost thats produced.
When less boost is required the the Boost Control Valve allows air into the BCS reducing the the vacuum and allowing the springs in the Turbo Actuator to open the vanes inside the turbo reducing boost.
If the size of the BCS pipes are increased the amount of air the Boost Control Valve has to allow back into the system is also increased, this can cause a short delay in boost control because airflow through the valve is limited, depending on requirements this can create turbo lag effect or over boost as the boost levels fail to react quickly enough.
This was explained to me by a guy who races diesels so I guess he knows what he's talking about, its the reason why most modern turbo's now have electrically operated actuators, as they can control a Variable Vane turbo far more precisely.
I'm sure the pipes on the missus's 147 are too big so i'm going to refit a set of original Alfa pipes.
Last edited by Shadeyman; 07-05-12 at 06:48.