what size bov do i need to get for a '89 rx turbo

you don't need/want one.

You want to use BPV not a BOV (bypass valve, not a blow off valve). The air travels past your MAF and the ECU tells the injectors to account for that air. Once you shift and blow that air to the atmosphere, your injectors are expecting that metered air and is supplying the fuel for it, and without it you get a rich condition.

 

It will make the car slugish after shifts. Sounds cool, but performs like crap.

 

A Bypass valve performes exactly like a BOV except it dumps the air back into your intake, after the MAF... so the metered air stays in circulation and your air/fuel mixture doesnt change.

 

I used a BPV from a Saab 900 turbo. It was manufactured by Bosch and you can find em real cheap on ebay, or next to free in the junkyard. Tricky part is plumbing it back into your intake.

 

I kinda rigged something up like this on my old RX:

 

And here it is installed with the SAAB Intercooler:

my -10 has a wrx intercooler and bov, and russ made it mount into the stock airbox to turbo rubber piece... therefor achieving bpv.Besides you want a RFL bov.. do a search on google

a bypass valve is not completely necessary. i cut out a piece of steel which covers the blow off valve hole on my 02 wrx intercooler. the thing i didn't like about the bypass valve routed back into the intake is that the throttle response wasn't nearly as good as the atmospheric vented bov or running no bov. the open bov made my car run horrible, woudln't idle and ran really rich. no bov isn't as bad for the turbo as people make it sound. i have put about 10k miles on my setup so far with no problems. it depends on what you want.

and it depends on how much boost you are running. with high boost you "can" put a lot of stress on a turbo with nothing.

a bypass valve is not completely necessary. i cut out a piece of steel which covers the blow off valve hole on my 02 wrx intercooler. the thing i didn't like about the bypass valve routed back into the intake is that the throttle response wasn't nearly as good as the atmospheric vented bov or running no bov. the open bov made my car run horrible, woudln't idle and ran really rich. no bov isn't as bad for the turbo as people make it sound. i have put about 10k miles on my setup so far with no problems. it depends on what you want.

 

10k is nothing. 250k is what your shooting for. And with increased boost, added intercooler, no BPV will make a short life for your turbo.

 

-Brian

The bov just saves the turbo from Spiking, when you let off the throttle that pressure has to go somewhere, and with no Blow off, it tries to go backwards through the turbo which in extreme cases = Shattered Compressor wheel.

10k is nothing. 250k is what your shooting for. And with increased boost, added intercooler, no BPV will make a short life for your turbo.

 

-Brian

haven't got that far yet, but i'm confident it isn't going to explode tomorrow.

Want a BOV, get an aftermarket ECU as well. Get a BPV and just stick it in.

You could also relocate your MAF and put it between the intercooler and throttlebody. That way the air that is blown off, has not yet been metered.