2004 WRX BOV or BPV?

[ben1272]

I know next to nothing about Subaru engines. Mine (from 2004 WRX) has a Blow Off Valve replacing its stock Bypass Valve. I am not a big fan of the 'whoosh' sound that comes with the BOV. I am not planning on running more than factory stock boost, so dont need/benefit from BOV. I am just beginning to investigate and have not yet determined where the BPV routes the bypass air....not even sure I still have a port for it as I believe I have some other aftermarket replacement parts on my engine.

I am curious if anyone has a thought worth sharing. I will probably leave as is for now, go-kart, and then over winter go back to stock BPV along with other needed fixes/mods.

Thanks in advance for advice....sorry kind of rambly!

-Ben

[phil1734]

The BPV should dump the air in somewhere just before the turbo inlet. Not sure where exactly it connects on these cars but that's where you should start looking if nobody else chimes in to help.

Most of the noise comes from any intake modifications done such as shorting the giant black plastic tube that runs up next to the fender or putting on a giant cone air filter. If you get those closer to stock the noise may reach acceptable levels.

[wleehendrick]

The BPV connects back to the turbo inlet hose, just upstream of the turbo itself. If your donor has a BOV, it probably has an aftermarket Turbo inlet hose; here's image I found online of a stock part. The left side clamps to the turbo and the BPV air is routed to the large fitting just upstream:

[wleehendrick]

and here's an image of an aftermarket inlet which labels where the BPV/BOV goes:

[ben1272]

Thanks. I am going to check if my aftermarket inlet hose has a BPV return tube.

[ben1272]

It does, and the hose to get to it is intact and just plugged near the BOV location on the TMIC. It looks like I could just purchase OE BPV and swap. My primary reason for considering this right now is that I read that BOV's carelessly added dont account for the required changes to the fuel mapping. The MAF sees the air, ECU meters the fuel accordingly, but then the BOV releases a bunch of air to atmosphere and engine runs rich. If consensus is this is not a problem, I may leave as is for now.

[phil1734]

For a fraction of a second, its a possibility.

The BOV/BPV only dumps when the throttle plate is closed, which means your foot is off the gas pedal and you should have a fuel cut-off anyway, regardless of what is flowing through the MAF.

[STiPWRD]

It looks like I could just purchase OE BPV and swap.

If you're interested, I've got an OEM BPV. I'm running an HKS BOV on my 818, my wife ran one of these on her evo for years. I used to run a turboxs BOV on my wrx for years without any issues. Some people don't care for the sound but we like it. As Phil mentioned, the throttle is closed (or closing) when the BOV is activated so there is virtually no load on the engine. It's really not a problem.

[wleehendrick]

If consensus is this is not a problem, I may leave as is for now.

The general consensus is that the slight, temporary rich condition may only be a an issue for the catalyst, but everything else is fine. If you don't have a cat, probably no worries.

[ben1272]

Thanks for the offer. Would you PM me what you would want for it? I will likely leave my setup as is through go-kart phase and then decide what to axe and what to keep over the winter. I do plan to buy an accessport....will this give me any options for dealing with the rich condition? I will be running cats given MA registration/inspection.

Pic of my engine.

IMG_7066(1).JPG

[STiPWRD]

PM sent. I'm not an expert on the accessport since I used to tune with the txs utec and now I'll be using Rom Raider but I'm sure the accessport will give you the ability to deal with the rich condition. You'll probably have to remove a bit of fuel in the 0% load column at the higher RPMs where you typically shift. I highly suggest having a boost gauge and wideband o2 sensor if you plan to do any tuning.