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WTB TT guru's boost questions


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Hey all


We have had this 1996 subaru legacy RS TT in the family for about 4 years and just driven it. Anyways about time it needs its boost sorted out.


Up intill today primary turbo had always ran at 15 psi and secondary at 8 psi for whatever reason its now started to boost around 8-10 psi in all gears but 5th will boost intill 15psi then switch on secondary and run at 8 psi. i dont know much about the whole TT thing apart from its a nightmare :P


Im sure something isn't working as intended boost seems quite low specialy on the secondary ? and the whole primary turbo boost changing is abit weird unless theres a air leak or one of the lines blocked? 


Only thing ever changed on the car since we had it was spark plugs fuel filter and oil lol.


ECU has no fault codes all is clear. 

Have no idea what turbos its running.

Model BD5B48D


Here are some pictures maybe something will stick out to someone.




Cheers all 

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"always ran at 15 psi " - on my 93 the primary ran around 9 PSI. 15 PSI sounds like bleeding too much either

a) vacuum leak on the lines

b) the boost solenoid is dud and not bleeding accurately.


Recently had my primary boost control solenoid play up - swapped it with the on in the second control box and got smoother behaviour. Then replaced the dud one.


"secondary at 8 psi " - secondary usually is around 11-13 psi, peaking at 15 near read line for me. Does your 96 have a secondary wastegate? I had the unfortunately experience of testing mine and having it jam open and lossing all secondary. Turns out carbon build up and rust scale of all things on the secondary wastegate port (unlikely experience). But if your boosting and boosting low that maybe a  factor.

Given your primary is way off I would more suggest a vacuum leak and/or the primary boost solenoid being an issue. Since that would also influence total secondary boost.

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Thanks for the info :)


Went over the car today found a few pipes that needed tighten up bov and intercooler pipes etc..  if 8-10 on primary is normal then that must be correct then.

Cleaned out the boost solenoid in the guard had abit of crap in it. secondary still having hard time on boost around 6-8 on full noise. Could be right with the wastegate i was thinking that.



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