Blow off Valve Placement

[ghia nut]

I have a rather interesting question here.
I have done some research on google and cant seem to find the answer Im looking for.
I know this is not a turbo question but deals with the BOV in relation to the intercooler.

Im modifying the placement of the AWIC to sit on top of the manifold as its going into a vw.
Pictures here.







If it were a perfect world, I could get or make a 2.5" od pipe with 2" radius bend at 170* and make it fit.
Then I could weld a port to connect to my BOV. But Im thinking Im going to have to resort to a 180* bend silicone hose as it will have some give but I cant find one with a port on it to connect the BOV up to.

The main question is, is it horrible for the BOV to be before the inter-cooler or not? I know Subaru usually has them mounted to the inter-cooler, and thats great. Ive heard people say its better for it to be before the intercooler etc etc and Ive heard the exact opposite from forums so Im a little confused.

Is it even worth worrying about?

[vrg3]

No, it's not horrible. In fact, the car that intercooler came from had the blowoff valve plumbed upstream of the intercooler from the factory.

It becomes a problem if you have a large pressure drop across the intercooler, either because it's a restrictive intercooler or because you're running high boost, or a combination of both. What happens is the pressure drop across the intercooler can make the blowoff valve crack open and leak.

There are different schools of thought about whether it's better to blow off air that's passed through the intercooler or air that hasn't; none of that matters all that much though. And if you use an atmospheric blowoff valve that part matters even less. Are you planning on using a recirculating blowoff valve?

What turbo are you planning on using? How much boost do you expect to run?

[ghia nut]

Currently its the stock VF11, would love for it to be a VF22 but thats a ways on down the road as I want to run stock at first to get my feet wet.

Blow off valve is HKS SSQV and I plan to recirculate it, so no fireballs of death and super rich fuel mixture. Stock boost levels for now. Will one day up the boost. Will also be using Greddy Profec Spec B boost controller.

Im a little concerned as I know that air before the AWIC is going to be hot, Ive read that that may cause the diaphragm to prematurely fail but havent found any one kicking and screaming about it.

[jefferson]

There is no intercooler on the stock ej22 and the recirc. valve works fine on it. I don't think the heat is anything to be concerned with.

Jeff

[ghia nut]

jefferson, your simple logic is spot on, completely didnt think about that.

[Legacy777]

Just to throw my two cents in. I've got the AWIC setup and have my BPV hooked up before the intercooler. It works fine, and IMO that is the way you want to do it.

Plumbing after the intercooler can lead to residual pressure at the compressor housing which "can" cause compressure surge. So putting the BPV or BOV as close to the outlet of the turbo will eliminate/minimize this possibility.

[S Webster]

Hey Ghia Nut, what did you say this is going on? Suby intake on a Vdub motor? I've been workinon a similar project, (mostly in my mind) for some time. I've built a 70 Ghia with a 2L 914 eng, TD04 blowin' thru a pair of 40mm Delortos. I'm so tired of constantly messin' with those carbs, I was thinkin' of using a 2L. WRX set up. Have you come up with a way to adapt the manifold around a fan shroud? Off subject I know, sorry. Thanks guys, S.

[ciper]

I have an AWIC in my shed with a blow off valve welded right onto its inlet pipe so it sits under the intercooler.

Why not just weld a 1 inch barb onto the intercooler inlet then run hose to wherever you'd like to put the valve?

I know its not the question asked but I highly suggest using a bypass valve. The OEM metal units from newer Subaru turbos are good for anything less than 21 psi without the crush modification.

[usliberty]

I was always told the bov should be placed as close to the throttle plate as possible. When the throttle plate closes under boost the charged air is hitting a wall and if that air builds all the way back to the turbo then it can abruptly srop the turbo. The shockewave from the throttle plate needs to be released asap so closer to the throttle plate makes more sence to me. If I'm wrong id like to see the reasoning cuz that's how I did my fmic. In a tmic there's not a lot of distance to make a difference but with a fmic its more air volume that's building up.