legacycentral bbs

So recently I installed a td04 and an FXT tmic. It went well until we got to plumbing the BPV. I purchased a BOV adapter for the tmic from ebay ( like the one in figure 1 ) thinking that WRX and FXT tmics were the same. I soon found a small but important difference between the two, the place where the stock BPV/aftermarket BOV adapter goes. On the WRX tmic it looks like an asymmetrical rounded triangle shape (like in Figure 2), but on the FXT tmic it looks more like a symmetrical rounded diamond shape (I couldn't find a pic of a stock FXT tmic). They are different enough shapes that the BOV adapter from a WRX tmic will not fit onto an FXT tmic. I ended up making it fit by cutting out the bolt holes (see Figure 3) and moving the adapter down but am unimpressed with the aesthetics of it and am unsure as to how long it will keep from boost leaking. So for people wanting to buy an 06+ WRX tmic, DO NOT settle for an FXT tmic unless you are going to be custom making your own BPV adapter to fit the stock Legacy BPV.

*added* I also later realized that the bpv is closer to the throttle body intake on an FXT TMIC than on a WRXs. The edge of a WRXs bpv is 1 1/4"s away form the edge of the throttle body intake. Where as the FXTs BPV is 3/4 "s from the edge of the throttle body intake which translates into and extra 1/2" of room when using a WRX TMIC. This may not seem like a lot but when you are that close to the throttle cables it makes a big difference. Also (but I have not officially confirmed this), the WRXs BPV is angled up slightly where as the FXTs is angled down slightly. All this together reinforces my previous statement of not settling for an FXT TMIC.

Figure 1:


Figure 2:


Figure 3:



*
FXT = Forester XT (Turbo model)
BOV = Blow of Valve
BPV = Bypass Valve

Do I need to do anything with mine? I bought the same 06 TMIC for a WRX and it came with the BPV off the WRX. Can I just use that and not hassle with what you did?

Could somebody explain to me exactly how a BPV works and a Blow off valve? It looks like there's a vacuum line that is coming off that BPV. Does the vacuum line control when the BPV opens and closes? Does it open when you shift and the vacuum changes or something?

I searched google and I think I understand the purpose of the BPV now. It's for when you left off the gas pedal and the throttle plate closes. Instead of having the turbo pushing air against the closed throttle plate and slowing down the turbine, it opens up the BPV and recirculates it back into the turbo to keep it going.

Makes sense.

even on a stock wrx tmic, the bpy will hit your throttle cables, you will have to get some sort of adapter to plumb into your stock bpv

So the 06-07 wrx tmic bpv plate would be different than the one on the fxt?

Cause I've got a 06 wrx tmic and the same bov adapter shown and it fits great.

yes, the FXT's BPV plate is a diamond shape.