im running an large ported jdm 90 tii engine and an S4 turbo. the turbo is proted (or so i was told) but im not sure how much. i can feather the throttle and keep it at a spcific psi, but under wot, the turbo just runs right up. highest ive seen it get was 15 psi with the stock boost setup. ive setup an MBC, but that doesnt have the slightest effect on it. im wondering if the wastegate isnt ported enough, or if the wastegate flap might be stuck or the actuator is malfunctioning. any way to test this without taking the turbo off?. i cant remove the turbo for about 3 more weeks (gotta wait til i get outta school) and im going to port it according to aaron cakes right-up. he should be recommended for sainthood for all the help he has given... haha

 

sounds to me like ur waste gate is not connected correctly (lines backwards perhaps)

remove the MBC.. and run a vacuume direct to the wastegate..

then see what the boost is and let me know

 

dont run vacuum, the source should be before the throttle plates, ideally right off of the compressor housing.

 

You might want to consider saving your pennies and go with a S5 turbo and exh. manifold.....it uses 2 wastegate ports instead of the S4's single small one. I picked up a S5 turbo on ebay for $65 and I'm using a t04b compressor wheel and housing from another turbo I bought on ebay for $30. Better twin-scroll setup on the S5 IMO.

 

i have the stock wastegate setup. not the MBC. dont see how it could be backwards. and im a little confused on how you want me to test the boost.



im saving my pennies for a 60-1.

 

When I had my twinscroll hooked up wrong it caused a MAJOR boost spike even with my ported s4 wastegate...