Increasing the boost pressure
The boost pressure is controlled by the actuator, which opens and closes the wastegate to regulate the boost pressure that the turbo creates. The turbocharger is a simple device which uses the energy of the exhaust gases to compress the air going into the engine, effectively giving it a larger capacity and thus more power for its size.
To increase boost pressure there are a few different ways of doing it but on a standard turbo the easiest (and free) method is to increase the preload tension of the actuator. Other methods are listed below. The actuator holds the wastegate shut using spring pressure. The turbo uses air pressure to move the actuator and so open the wastegate. If you increase this spring pressure by shortening the rod that connects the actuator to the turbo then you will increase the air pressure that it opens at and thus increase the boost pressure of the turbo. However there are a few warnings here to give:
1. Ignore any instructions from people who say if you turn it X amount it will up the boost Y amount. Cars differ and the actuators age at different rates so you’ll never get an accurate result this way.
2. Don’t up the boost too far! 19psi is what I’d consider safe on a standard L series turbo. As you up the boost further the turbo becomes less efficient negating the effects of upping the boost further and the bearing starts to suffer, i.e. the turbo life is shortened. On a recent rolling road I saw a car make more power at 20psi than it did at 23psi to highlight the point. I know which boost level his turbo will last longer at!
3. Really you need a boost gauge to set up the boost accurately. On the 2/4/600 intercooled models that aren’t fitted with any tuning boxes you can use the fact that the standard boost cut level is set at just over 19psi to set it up. However be aware that the boost cut does not activate until the boost level has been exceeded for 2 seconds so you’ll need a long straight high-speed road to set it up like this.
It is far easier to install a gauge temporarily if necessary and this is what I’d recommend.
Ways of increasing the boost pressure
Several methods are available all of which have benefits and drawbacks
1. Shorten the actuator rod
+ Free, Works well for boost pressures close to standard
– Doesn’t work well for big changes from standard, Wastegate starts to open slightly before the set boost pressure is reached
Conclusion: Easy and simple first step
2. Fit a bleed valve
+ Cheap, easier to adjust although they can be very sensitive
– Wastegate starts to open slightly before the set boost pressure is reached
Conclusion: If you’ve got one sat in a draw then you can try it but otherwise included for completeness really, other methods are preferred.
3. Fit a ball on spring type mechanical boost controller
+ Cheap, easy to adjust, eliminates the wastegate starting to open early
– Can take a while to set up
The next most preferred method of boost control
4. Fit an electronic boost controller
+ Adjustable on the move, lots of different functions
– Harder to set up, expensive and require space to mount inside the car.
Conclusion: Probably more worthwhile on a more highly tuned car.
For more practical information on how to alter the boost pressure please see here