Seriously?
You are all noobs listening to noobs.......And none of you seem to have a grasp on the big picture.....
(ignoring the boost T for a second) Your 99-00 WRX will run lean with a CAI, silicone intake & a 3" system with a STOCK
ECU (so much so that you'll be lucky to move it...Ask Damo), if it does come on boost it be lean & WILL ping it's tits off.
Boost tee's are ghetto spec.......They are shit, they spike to fuck.
If you want to risk a $10,000 rebuild on a $100 boost control DOWNGRADE go ahead & prepare to be laughed at when it all goes to shit.
You are mad to think a ball bearing and a spring are better than self checking
ecu with defined limits and active control.
An Rs lib runs a dumb 8 bit
ecu.....It has a looser emission regime compared to the 99-00 16 bit
ecu which runs much tighter control of fuel & ignition (and has limited self learning - ignition timing only), which is tuned for the stock intake system.
Not to mention that the design of the engines between the two are quite different.
The stock boost control system is more than adequate to control up to 1.7-1.8 bar with a decent plug & play
ecu...........I'm running 1.7 bar using all the stock boost control on my 99 STI (same as on your WRX btw) but using a power FC
ecu.
P.s why would you use a boost tee if you are running stock boost anyway????