Boost Drops Why???
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Joined: Sep 2005
Posts: 44
From: Miami
Car Info: 2006 WRX Gray
Boost Drops Why???
I have on my 06 WRX a bellmouth DP, Greddy EVOII exhaust. My stock turbo had the wastegate ported and polish. I was having problems with spiking so I bought A high performance MBC from TuboXS. I was able to adjust it to a max boost of 14.5. I tested several times on 4th & 5th gears @max RPM. What happens is it get to 14.5 and hold for about 1500rpm then it starts to drop. It will drop down to about 11.5 @5500RPM and maintain at that level. Someone at the local speed shop told me that this is normal because the internal wastegate wont hold that much pressure. Is that true? Is there any adjustment that can be made to the actuator arm on the gate itself. These are only temporary means until they come out with a UTECH for my car. Also I made sure there were no leaks on the hoses leading to and from the MBC. Please advise!!!
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Car Info: 2005 LGT wagon
Please remove the MBC, as it is killing your car!
Subaru has spent a lot of time engineering a control system for the turbo on these cars.
It works like this:
The ECU is mapped for various boost levels at various rpms.
As long as the knock sensor doesn't detect any knocking, the ecu will allow as much boost as allowed by the map.
The wastegate starts to open at about 10psi, but the boost solenoid keeps the psi that goes to the wastgate accuator lower than this as long there's no knocking.
For example, if knocking is occuring at 12psi, but the MBC is set to 14 psi, the ECU can't bleed of boost, and your engine will suffer.
Subaru has spent a lot of time engineering a control system for the turbo on these cars.
It works like this:
The ECU is mapped for various boost levels at various rpms.
As long as the knock sensor doesn't detect any knocking, the ecu will allow as much boost as allowed by the map.
The wastegate starts to open at about 10psi, but the boost solenoid keeps the psi that goes to the wastgate accuator lower than this as long there's no knocking.
For example, if knocking is occuring at 12psi, but the MBC is set to 14 psi, the ECU can't bleed of boost, and your engine will suffer.
Thread Starter
Registered User
Joined: Sep 2005
Posts: 44
From: Miami
Car Info: 2006 WRX Gray
If the engine is knocking wont the check engine light come on? Is the MBC unsafe at any boost level? What if I lower my max boost to 11psi?
Last edited by 06WRX420; Dec 5, 2005 at 10:49 AM.
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