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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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Discussion Starter #1
Just bought the car and love it, but I could swear that the boost is inconsistent. Sometimes it hits hard and is spot on, sometimes I have to wonder if the blow off valve is stuck open. I was planning on putting a boost gauge in anyways and there seem to be lots of options, all of which are a pain to install. Any advice on choosing one over another?

Also - If I were to replace the blow off valve and wanted one that didn't require re-tuning but was just a better drop-in replacement for the stock one, where should I be looking?
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #2
The install on the gauges seems more difficult than I pictured, so I think I'll just replace the BOV and see if that takes care of it. Seems like the most likely problem, though if this doesn't do it i'll probably put in new vacuum tubes next. Turbosmart seems to have some reasonable drop-in replacements for the stock BOV, does anyone have an opinion on this one? Product | Kompact Plumb Back Mazdasubaru | Turbosmart USA
 

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05 OBXT Limited AT
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22 Posts
Welcome and congrats on your new purchase! I have no idea about your background with tubo'd cars, so forgive me if you already know the following -

It is not out of the ordinary for the seat of the pants boost feel to be inconsistent. The feel is influenced by not only rpms and resulting boost pressure, but also vehicle speed and gearing. There are a few sweet spots for that nice strong kick that pushes you back in the seat. However, there are also spots where you will be making a bunch of power and just not feel it as strong due to the above. At least, that's what I have noticed.

Have you found the legacygt.com resource yet? Go over there and check it out, lots of additional information in the technical forum section for turbo powertrains. Do a bunch of research before dropping the the cash on a BOV. For about the same amount of money as the one you referenced, you could get a light aftermarket tune that will probably give a much greater performance increase over a BOV.
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #4
I've had one turbo'd car prior to this (SAAB 9-3) that took a bit of consistent tinkering to keep running well. I had some similar issues with it and wound up having to replace the BOV, and after I did I wished I'd done it earlier, there was a substantial change over the stock plastic one. I'm familiar with the load not RPMs impacting the feel, but even from a stop the XT feels different at times. It may just be normal for this car, but it even sounds different after some gear changes than others when you'd expect an "exhale" sound (I'm not talking about a chirp, I'm trying to keep this thing quite and just re-circulate).

EDIT: PS - I did find that legacy gt site earlier, it's awesome as **** what you can easily change on this car! I'm pretty excited and can't wait to screw something up ;)
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #5
The new BOV came in today, install was super easy. Looking at the old one this new one is clearly much better made and designed, but I think the main problem with the old one was the gasket had a malformed section which may have prevented it from sealing all the way. In my initial drive to the store and back it seemed a little quicker off the line but I could really only do so much on city streets during rush hour. We'll see how it does on the commute tomorrow.
 

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05 OBXT Limited AT
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Sounds good so far! Let us know how it turns out. I'd be curious to hear your thoughts after the swap settles in a bit...if the inconsistencies with boost feel goes away.
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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Discussion Starter #7
After about a week of driving this does seem like an improvement but doesn't seem to have fixed the problem.

I'm thinking what I may need is a manual boost controller, but I'm not convinced as I don't fully understand what's happening.

This is an automatic, but this is what I've figured out:
First gear the boost always works fine now. This was not the case with the old valve.
Second gear I believe the boost always works fine but as it's an automatic I can't swear to knowing when I'm in second.
Third and above is where the problem is. After shifting under load the BOV doesn't seem to re-seal with any sort of predictability. If I didn't keep on the gas through the shift and hit the gas enough to use the turbo it just doesn't hold with any real amount of pressure. It sounds (and feels due to the lack of power) like it's venting at least partially. If I kept on the gas through the shift and I'm still trying to accelerate I'm almost certain that it's still partially venting.

Part of me thinks I need a stiffer spring in the BOV, part of me thinks I need a manual boost controller, part of me thinks I need both, and part of me thinks I don't know enough about this that it couldn't still be something else entirely.

ANY and all thoughts would be much appreciated.
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #9
Just going by gut at this point, but something really feels and sounds off.
 

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Well-loved 2006 2.5XT
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These cars have the "sport shift" mode. "Sport" mode always kicks it better for mine. Also, I've found that once I've "engaged" the turbo once or twice playfully, she seems more willing to blow somebody off the road when I want her to.
 

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05 OBXT Limited AT
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What do you mean by "sounds"? I have never noticed my completely stock XT to produce the atmosphere venting BOV sounds some turbo vehicles make. Maybe you have an intake leak causing funny sounds/performance, they can a PITA to locate sometimes.

For an in depth look at BOVs/BPVs:
http://legacygt.com/forums/showthread.php/technical-info-bov-bpv-set-up-and-operation-150687.html

In case you would like to try logging to see what the boost numbers really are:
http://legacygt.com/forums/showthre...e-tuning-vendor-and-vag-com-cable-158118.html
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #13
If you turn off the ac and the radio you can hear it. It doesn't chirp or anything, but there's a "shhh" sound. I didn't realize what a difference sport mode made, I thought that was just to flip through the gears manually, which it did too slowly to be all that useful. I took the long way home today and it behaved much more the way I would have expected it to.
 

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"Honey Badger" 2005 OBXT Limited 5EAT 108K+ miles
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107 Posts
i hear a "shhh" sound with my XT when accelerating with the radio turned off as well. i just always assumed i was hearing a turbo spooling.
 

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05 Xt beatin' to an inch of its life
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620 Posts
Unless you actually know you what the boost is doing, you're chasing phantoms.
This^. Install a boost gauge. I believe what you are describing is the torque converter's lockup strategy. Power delivery can feel depressed when its unlocked in the higher gears. You can install a lockup switch, but that should only be done once you determine the car is healthy.
 

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2008 OBXTLtd 5MT
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52 Posts
I have been following this because I feel like my boost is inconsistent as well. Don't have a boost gauge and haven't done any troubleshooting, but I do have a manual transmission so the torque converter can't be an issue in my case.
 

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05 OBXT 5eat stg1.2
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Inconsistent power could be a lot of things. The only way to find out is to do some datalogging. All it takes is a vag-com cable, a laptop, and free software. It could be heat soak, knock, etc.
 

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'06 OBXT 5EAT 1.5" lift, stage 1 tune
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49 Posts
Discussion Starter #18
Manual boost controller and VAG-COM cable ordered. I wanted both of them anyways as I'd also planned on doing a stage 1 ECU tune and just like tinkering with things. I went with TurboSmart again and got the boost tee, I considered going with perrin or a few other brands but the price was right on this, I didn't see many bad reviews, and I liked that it has a locking set screw for the knob so I know my adjustment won't slip once I set it.

I still want a boost gauge but it's just not in the budget right now so that will have to wait. I'm thinking that mod for the cubby hole that turns in into a 2-din case using half for sensors and half for a new radio with bluetooth is in my car's future.

Edit: I also meant to ask about this lockup switch, where can I read up on this? I'm intrigued. What benefit will it have to me, what could I kill by doing this, how hard and expensive would it be?
 

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05 OBXT 5eat stg1.2
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You absolutely do not need a manual boost controller. It's pointless when we have access to the ecu via vag-com. The stock ebcs can handle way more than the stock turbo can throw at it.

There are a lot of reasons why a MBC is a bad idea, but I'll just give one for now. If you get a tank of bad gas, the engine will knock. The ECU will pull timing, and if it still sees knock, it will cut boost down to wastegate pressure. You're bypassing a very important failsafe. If for some reason you end up with a lean condition from a vac leak, your engine will assplode very quickly due to the inability to cut boost!
 
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