partywagon42

Looking for some input and suggestions on bypass valves.
I have a 2004 wrx wagon. Relevant modifications as follows: turbo xs utec, invidia catless up pipe (no flex joint), Megan racing 3" downpipe to 3" magnaflow exhaust (all catless), sti injectors, spt cold air intake/air cleaner.

I am far from an e pert on forced induction, but with my engineering background I do understand the concepts.

Previous owner had the car tuned for around 15.5psi (metric gages). From what I understand this is the upper limit for the factory TD04, due to the volumetric flow rate. In higher gears at wot, boost begins to taper off. I know that this could be due to the flow rate, but I have also read that aging factory bypass valves tend to have trouble holding higher boost. So I'm looking in to upgrading to an aftermarket unit.

I understand that venting 100% to atmosphere with a mass air flow based system will cause the car to run rich when pressure is relieved. I have seen several aftermarket units that have the option of venting 50% to atmosphere. Is this enough to make the change in A/F negligible? Does this help with throttle response? Would there be any noticeable advantage with 15-16 psi, or should I stick with 100% recirc? I will say that I love the sound of a nice blow off valve...

What systems are you guys running and what do you suggest?

ddavis

iTrader: (4)

You don't need to be concerned about maxing out the stock bpv until you start getting over 20psi boost. Subaru's like 100% recirculating bpv's and they run best with them. I would recommend sticking with the stock one unless you start hitting higher boost levels. At that point, Cobb & TurboSmart both make very good higher psi bpv's you can use.

If you want more sound you can remove the intake silencer in the car. Looks like you already have an intake, that was going to be my next suggestion

partywagon42

Ok thanks for the info. The spool is pretty loud. What's a typical lifespan for the factory piece? It's a mechanical device that regulates a fluid, there has to be parts that wear, springs that lose pressure, seals that deteriorate eventually. Being a 2004 with 140k hard miles, any chance it could be old and worn out?

ddavis

iTrader: (4)

They can start to seperate and leak over time. My stock one had around 100k on it and was fine before I swapped it. Theres no fluid in it, just air and you could always do a boost leak test and pressurize the system to see if your getting any leaks in your system.

partywagon42

Fluid can refer to liquids and gases (and solids in some situations), but yea pressure test would be a good idea. I wouldn't be surprised if I had a leak somewhere aside from the bypass valve, since all of the hoses are old and brittle. I broke and had to replace/repair a few during the overhaul. I've only put about 20 miles on it since. Thanks for the advice man!

partywagon42

I actually got some useful information from this thread aside from the usual "throw away the utec or use it as a paperweight" haha thanks again

ddavis

iTrader: (4)

No prob, good luck with the car!

partywagon42

Thanks brother. Going for inspection tomorrow, have to put a few more miles on it first to make sure there are no "incompletes". Fingers crossed for no codes

Superusdm

iTrader: (6)

If you haven't already found this through your research, you can modify the stock bypass valve to operate differently so it will hold more boost without leaking. I'd imagine the same modification will help ensure your aged valve will not leak at lower boost levels.

In stock form the oem bpv is completely sealed, it receives feedback from the intercooler while under boost - pushing the valve towards the open position. At the same time the other side of the valve receives a pressure feed from the hose connected to the manifold (the main boost feed to the bpv). The spring aids in holding the valve in the shut position until the throttle is released.

To modify the valve properly, you tap and plug the feed coming from the intercooler and drill a small hole in the connecting air channel, by doing this you eliminate any 'opening' pressure coming from the intercooler altogether. I have noticed with this setup, however, that at lower boost levels I get some compressor surge, which doesn't bother me - and according to Go Fast Bits a properly tuned BOV/BPV will cause a small amount of compressor surge before opening.

I would do a little research to see what you can find about running a modified oem bpv consistently at low pressure, just to be safe.