legacycentral bbs

OK. well i got a 02wrx intercooler for cheap, so im going to install it soon i hope. BUT do i need to run a BOV? i want to keep my car as stock as humanly possiable. Couldnt i just bold a chunck of metal over where the BOV would be?

You need to reinstall your stock bypass valve, or the WRX one. Don't run a Blow off valve.

You can fabricate your own, or for about $40 on Ebay, you can get a BPV adapter which will bolt on to where the BOV should go on your IC.

The only other thing you would need to do is either get a stock wrx BPV hose, or get something at the autoparts store because the stock Legacy hose is much smaller than the fitting on the adapter you would buy.

So i could run the stock valve! Do i need to dissconnect it when i install an intercooler? cuz really i dont care for the sound of a BOV i just want the performance of having a intercooler!

You MUST run a BOV/BPV or you will kill your turbo and your motor. The BPV controlls the amount of boost that is generated by the turbo. Without it the turbo will continue to spool up increasing pressure until the turbo maxes out. Your motor and turbo will not appreciate this at all.

The BOV/BPV re-directs air from after the turbo, but before the throttle plate, back to the intake prior to the turbo. This is how it regulates the pressure level in the intake tract during part throttle senarios and also at WOT. You can re-use your stock one with the adapter setup that Bdub suggested. Do some searching on your specific IC setup and I suspect you'll come across some clear pictures and diagrams showing this.

I thought the wastegate actuator in conjunction with the wastegate itself controlled how much boost your turbo makes.

I though the BOV/BPV merely regulates that amount of residual pressure left in the intake tract prior to the TB when in partial throttle or in closed throttle conditions. I say intake tract in the case where an intercooler is not present. Doesn't the presence of a BPV vs a BOV also aid in reducing turbo lag ever so slightly when shifting?

And yes, you need one and a recirc valve (BPV) works better in our cars.

The BPV/BOV does not control boost, whatsoever. You can run a really stiff valve to aid in boost recovery, but that is at the expense of turbo longevity.


They do open some when at high rpm and low throttle, but your turbo is still going to move as fast as it will, no matter if it is open or not at that point. If the load isn't there and the throttle isn't open enough, there is not boost in the manifold. There may be some boost in the piping when the throttle is nearly closed and whether or not your BOV is open depends on its spring rate or adjustment.



If you want a really nice BPV, get the new recirc TiAL. It outflows the classic TiAL.

The BOV may not the actual component that controls the boost but the BOV system does. The point was that without it your will have boost regulation issues and other issues related to not controlling the air intake. My apologizes for the over-simplification.

so i need a BOV then... poo. Well then how hard could it be to get a 02 wrx intercooler with BOV combo to work. Because thats what i got.

There are several recirc valves that bolt onto the WRX intercooler. Do some searching and you have several options.

I need to clear this up for you guys--

You NEED a BOV, POV, recirculation valve or whatever you want to call it. THEY ARE THE SAME THING.

All this component does is dump air out of the pressurized intake track upstream of the throttlebody when the thottle closes. If you try to block that port off, you will have a major boost spike when you let off the throttle quickly (like gear shifts). This will slow your turbo, in some cases, it will actually cause the turbo to spin backwards for a moment! In some rare cases, it can cause the compressor wheel to unscrew and the compressor wheel and compressor housing will be destroyed.

This is not the only reason to have a BOV. The main reason is performance.
This allows the turbo to continue to spin at high speeds betrween gear shifts, so you will have instant boost when you open the throttle again for the next gear. If not, your turbo will have to be spooled up again at the bottom of the next gear. (turbo lag)

The factory systems dump this boosted air back to the inlet of the compressor because the MAF has already metered it. Otherwise, if you vent the BOV to atmosphere, your engine will run a bit rich for a second because the ECM is adding fuel based on that air that is no longer in the system. Personally, I have mine vented to atmosphere. The split second if richness noticably doesn't hurt my performance and it doesn't have a noticable affect on performance or fuel economy. The reason is- the ecm already decided to add the fuel, regardless of where the air for that portion of fuel is. And- you are at a closed-throttle position. Who cares? What is a little extra richness gunna do, cool your intake valves? Again, who cares. It's way easier to blumb it to atmosphere.

soo this info seems fit my question! I can still run the stock 93 legacy turbo recirculator valve! I can then just put a metal plate where the 02 WRX BOV was on my intercooler.

Tommio RS wrote:soo this info seems fit my question! I can still run the stock 93 legacy turbo recirculator valve! I can then just put a metal plate where the 02 WRX BOV was on my intercooler.

yup, the stock bov is small but so is the intake volume. The wrx bov will dump the boost a little faster than the legacy model, but the legacy model is way better than nothing.

If you upgrade to a front mount system, the stock legacy bov won't work that well in such a large volume.

OOO Right! You made my day Bro!

Say hello to stock valve action!