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SilverGhost
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Sydney
Registered:
September 2004

Re: Overboosting ST185

Wed, 11 May 2005 16:55

cutsGotBoost wrote on Mon, 24 January 2005 18:41

i didnt mean the vsv was a myth, just how people think its a "low boost" in first and second. i think it bleeds are away from the wastegate to allow equal boost in first and second, because there might not be enough load on the engine to get to full boost.
also 7 psi would be standard boost in a 1st gen.

I know this is an old thread, but im currently researching this topic myself and have to set the record straight. It is true that the job of the T-VSV is to bleed air away from the actuator, but your looking at it the wrong way round (I did exactly the same thing until i nutted it out too Smile

)

The stock ST185 actuator is rated to 6 psi before it starts to open the wastegate. What the T-VSV does is it stays shut in first and second gear so that full pressure from the turbo is acting on the actuator limiting boost in those gears to the actuators rating.

Once you hit third gear is when it starts bleeding air. The amount of air it allows to bleed away from the actuator is controlled by the ECU which gets the MAP pressure from the Turbocharger Pressure Sensor. This is how the ECU regulates the standard boost setting of about 8-9 psi in the higher gears.

Further to this the reason why you need to block the lines going to the T-VSV when installing an aftermarket boost controller is that the ECU is oblivious to it, so when your in 3rd gear or above the ECU will continue to use the T-VSV to bleed pressure away from the actuator at the same time that your aftermarket boost controller is bleeding pressure which is what you dont want. Obviously the only way to successfully control boost pressure is to have a single point where boost pressure is bled away from the actuator, because from either point of view the second 'bleed valve' is essentially a leak, which renders your aftermarket unit useless.

Hope this clarifies the matter.

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