One of the simplest ways of improving the performance of Turbo-charged cars is to increase the level of boost. This can be achieved in many ways, including the re-programming of the cars ECU (e.g. EcuTek), fitment of a higher-spec'd ECU (Prodrive, Link, Motec, etc..) or by the use of a manual (or electronic) boost controller.

Re-programming and new ECU's is the most expensive method, but this does allow more than simply increasing boost. The ECU can be tailored to run boost at certain engine loads, increase fuelling where required, advance ignition timing, etc.. This has then benefits of getting all the performance out of a car whilst maintaining elements of safety for the engine.

An electronic boost controller allows the drive to alter boost from inside of the cabin and provides some monitoring functions, so additional gauges may not be required.

The simplest method (and cheapest) is to use a manual boost controller. As it's name suggests you simply dial-in the desired amount of boost and this is fixed. if you wish to alter the boost, you must manually adjust the device.

A very popular manual boost controller for the Impreza is the Dawes Devices Hyprid Boost Controller.

This device uses a thumb screw to allow simple adjustment to the amount of boost and can be installed (or removed) within minutes.

Fitting Instructions - (UK Impreza '99 & '00)

Installation does vary on models of Impreza, but the following instructions work on the MY99 and MY00 models.

Initially I would advise you to fit the Dawes at it's lowest setting. Then, gradually increase the boost to the desired (and safe) level. When increasing boost from stock levels, you are introducing more stress on the engine. It is important to monitor fuelling, knock/detonation and boost so I would strongly recommend you have gauges in your car that can give you detailed information on these before running increased boost.

The Dawes has no preset boost settings or markers on the device, so you must have a boost gauge fitted to see just how much boost you are setting with the controller.


First remove the black rubber tube from the nipple on the Turbo Wastegate.


Next remove the tubing from the nipple on the Turbo Inlet. Also disconnect the long tube from the T-piece shown in the picture (left).


You should be left with two pieces of tubing and a T-piece.


Now to connect the Dawes MBC. Connect the top of the device (with the elbow & bleed hole) to the Turbo Wastegate nipple. Connect the bottom end to the Turbo Inlet nipple. Use the metal clips from the OE tubing to secure the device in-place.


Put a screw in the spare tubing and use a tie-wrap to secure in place.

Now that the device is installed, take the car for a drive (letting it warm up first) and see what amount of boost the car is holding on Wide-Open Throttle (WOT). Then simply increase the boost gradually, checking your gauges with each increase.

Please do not simply set the device to it's highest setting. Too much boost can easily damage your engine, so care must be taken to look for incorrect fuelling, increased knocking / detonation and (if possible) high exhaust gas temperatures.

The stock Subaru ECU also has a maximum boost setting (referred to as the Fuel-Cut), where it prevents the car from running too much boost or protecting it from sudden boost spikes. If you hit the Fuel-Cut level, this can be quite severe (violent engine braking) and could easily lead to loss of control if it happens unexpectedly or causes the car to become unsettled (mid-corner, for example).

Take care and don't go mad with boost settings and everything should be fine.