View Full Version : Overboost

04-01-2001, 21:13
I know this has been discussed before but my car is now overboosting and im looking for ways to control the overboost. Has anyone found a solution? if an electronic boost controller is fitted(i.e HKS/APEXi) how do these prevent overboost and what advantages are gained by using them.

RS Pilot
05-01-2001, 16:08
I'm not sure if this is what you are after but you can manually change the boost by adjusting the wastegate actuator setting. The actuator is linked to the wastegate by a threaded rod. This is what's used at the factory (turbo manufacturer, not Mitsi) to set the boost. Inside the actuator is a diaphragm and a spring. To lower boost, the rod can be adjusted to take preload off the spring. Just had a quick look at my EVO1 - you need to screw the rod into the actuator to lower the boost. I would make adjustments of only half a turn at a time until the boost is at the level you require.

I used this mod many years ago to tweak my Uno Turbo up 4 psi of boost [img]http://www.ltregister.f9.co.uk/graphics/biggrin1.gif border|EQU| 0 align|EQU| absmiddle ><!--e13-->

I'm not sure what system Mitsi use to control overboost (haven't looked particularly hard) but if it's an overboost switch then this can be adjusted also. By increasing the preload of the spring in the switch, the overboost setting can be lifted slightly. Be very carefull if you take this route - you need to know what maximum boost the engine can take safely.

By the way, if you remove the grommet from the actuator pipework your boost will build up too quickly and cause a 'spike' of overboost before the system drops it back to normal levels.