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I was wondering if anyone considered putting on a new blow off valve on our current ascent turbo. I know that some can push air back into the turbo and may require a time due to this but is there one that is similar to OEM for a louder sound?
 

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I was wondering if anyone considered putting on a new blow off valve on our current ascent turbo. I know that some can push air back into the turbo and may require a time due to this but is there one that is similar to OEM for a louder sound?
I think you'd find it difficult with the Ascent's piping. And, among other things, the Ascent uses an electronically controlled, servo driven, continuously modulated, variable wastegate with (IIRC) 255 different open positions. I think you'd really piss off the computer by adding one.
 

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Blow off valves sound best on a manual tranny when you shift gears. With our cvt I don’t think you’d get the same effect.
 

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The blow off noises aren't going to come from anything to do with the wastegate, different parts of the turbo system altogether. A panel filter or intake upgrade would be more likely to give you some noise, or a 50/50 hybrid valve but you would want a tune for it. Its all a lot of work and money for some worthless noise in my opinion. The reason for the Bypass Valve vs Blow-off valve is the MAF system, all air entering the intake tract is metered and fueled appropriately, allowing metered air out of the system via a BOV would result in a rich condition which the ecu would not like.
 

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The blow off noises aren't going to come from anything to do with the wastegate, different parts of the turbo system altogether. A panel filter or intake upgrade would be more likely to give you some noise, or a 50/50 hybrid valve but you would want a tune for it. Its all a lot of work and money for some worthless noise in my opinion. The reason for the Bypass Valve vs Blow-off valve is the MAF system, all air entering the intake tract is metered and fueled appropriately, allowing metered air out of the system via a BOV would result in a rich condition which the ecu would not like.
Exactly, and thus the ECU would go crazy trying to make the wastegate make up for it, slamming it open only for no boost to be found.
 

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Exactly, and thus the ECU would go crazy trying to make the wastegate make up for it, slamming it open only for no boost to be found.
Not exactly the two work at different times they wouldn't overlap unless the BPV was leaking, which is completely plausible given Subaru's history with them. The wastegate is normally open and the BPV is normally closed.
 

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Not exactly the two work at different times they wouldn't overlap unless the BPV was leaking, which is completely plausible given Subaru's history with them. The wastegate is normally open and the BPV is normally closed.
The Subaru Ascent wastegate doesn't have a normally open position. It only has 255 different stages of variably open, that continuously change to ensure we never exceed a mediocre boost that's a far cry from the 22 or 24 psi that the MGT22 can handle in design range.

It's not easy to determine when it's closed. I spent a bunch behind the scenes discussing this with some tuners, as well as ensuring they realized the data they were looking at wasn't correct (they were only finding "open" and "closed" which didn't match what it was doing at all).

There's the problem. The wastegate can indeed be open or closed, or in 254 other stages of not fully open but not closed, and, one needs to know how to figure that out. COBB figured it out, and the tuners I was chatting with eventually did too...

Serious Question:
So, my question is, how does one tie that (the digital "I'm really open - I am not at 0.7% open or 47.3%") to a BOV?
 

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The Subaru Ascent wastegate doesn't have a normally open position. It only has 255 different stages of variably open, that continuously change to ensure we never exceed a mediocre boost that's a far cry from the 22 or 24 psi that the MGT22 can handle in design range.

It's not easy to determine when it's closed. I spent a bunch behind the scenes discussing this with some tuners, as well as ensuring they realized the data they were looking at wasn't correct (they were only finding "open" and "closed" which didn't match what it was doing at all).

There's the problem. The wastegate can indeed be open or closed, or in 254 other stages of not fully open but not closed, and, one needs to know how to figure that out. COBB figured it out, and the tuners I was chatting with eventually did too...

Serious Question:
So, my question is, how does one tie that (the digital "I'm really open - I am not at 0.7% open or 47.3%") to a BOV?
Semantics, throttle closed, when the BPV would be working, would call for the turbine side to be releasing pressure. In previous vehicles including my 2010 legacy that meant 0% wastegate duty cycle. 100% duty cycle was closed 0% open, whatever the servo position it means the same thing, bypass as much exhaust as you can. Position 253, 247, 235...doesn't matter the theory is the same
 

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Semantics, throttle closed, when the BPV would be working, would call for the turbine side to be releasing pressure. In previous vehicles including my 2010 legacy that meant 0% wastegate duty cycle. 100% duty cycle was closed 0% open, whatever the servo position it means the same thing, bypass as much exhaust as you can. Position 253, 247, 235...doesn't matter the theory is the same
Except, it absolutely isn't, and that wastegate is far more active than you'd imagine. I've looked at the data. Tuners had problems with it because it doesn't act anything like the older Subaru open/close/flutter wastegates. There is no zero and 100%. And when they thought they saw fully closed, it was indeed open.
 

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Except, it absolutely isn't, and that wastegate is far more active than you'd imagine. I've looked at the data. Tuners had problems with it because it doesn't act anything like the older Subaru open/close/flutter wastegates. There is no zero and 100%. And when they thought they saw fully closed, it was indeed open.
Its still semantics, the turbocharger works like every other turbo ever made, it just has a (hopefully better) wastegate control which allows a semi-open wastegate rather than a duty cycle of open/close.
 

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Its still semantics, the turbocharger works like every other turbo ever made, it just has a (hopefully better) wastegate control which allows a semi-open wastegate rather than a duty cycle of open/close.
Right, but that's where things confuse me. The wastegate is rarely fully closed in most people's drives. But, the wastegate is also rarely fully open - including when you ease up on the pedal. The exception to this being when the car is in auto, shifts into "fake 8th" and drops to 1,700ish rpm - pretty sure that 'gate is in some stage of closed almost all of the rest of the time.

So, if the wastegate is being held in any position where the ECU is expecting boost, and the BOV flips, then, the ECU will try to compensate. We can surmise it does that from watching how it works very hard to maintain the specific boost it wants - and does so. The FA24F gets a flat 277 lb-ft of torque because of precise boost control and boost limiting to the bottom of the MGT22's boost range. The data was really neat to watch.

I've made the Ascent do dumps. It isn't that easy, and I didn't have the luxury of having the recorders hooked up at the time to see if it actually fully opened the wastegate or not (fully opened, or was trying to maintain some boost).

So, the question is, how would that work? I can't see how putting a BOV in would do much except in rare circumstances where the Ascent ECU actually requested a fully open wastegate, because, at any other time, when that boost starts to drop because of the BOV, the ECU will move the wastegate more shut to compensate.
 

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Probably the only time it would open would be a wide open throttle position probably in low to mid rpms and then abruptly letting off the throttle, and even then it wouldn't be open for very long. If someone was tuned for more pressure and aggressive power it may be opened more often but on a cvt equipped turbo probably rarely. In all my 7 years of having my Legacy I have never heard my bpv open, I guess I don't drive it hard enough. The Ascent has a small turbo, it isn't going to be flowing incredible amount of air ever.
 

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But again as I mentioned earlier Subaru has a history of leaky bpvs in their cars, I've not been convinced that has changed yet, and it would be impossible to know without actually testing it. Some have leaked at as little as 8 psi, so it could very well be the stock unit seeps some boost all the time anyway.
 

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Probably the only time it would open would be a wide open throttle position probably in low to mid rpms and then abruptly letting off the throttle, and even then it wouldn't be open for very long.
That's exactly what the data showed. And that's exactly how I get it to do so. Oh, doing really steep climbs and making it work at low RPMs (and then quickly letting up off the gas) will do it too.

The Ascent has a small turbo, it isn't going to be flowing incredible amount of air ever.
Well, I wouldn't call it small. It's bigger than many STI and WRX turbos, and does great moving Ford F150's and various heavy luxury cars. And it's barely boosting in the Ascent. 15ish psi, maybe 16 psi on bursts before the ECU clamps it down... but it could be doing 22-24 psi (per Garrett/Honeywell).
 

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But again as I mentioned earlier Subaru has a history of leaky bpvs in their cars, I've not been convinced that has changed yet, and it would be impossible to know without actually testing it. Some have leaked at as little as 8 psi, so it could very well be the stock unit seeps some boost all the time anyway.
I dunno. It will be interesting to see. When Subaru commissioned Honeywell to make the "brand new turbo" (Dominic Infante, Subaru VP - new variant really), I think they had the creation of something new and better in mind. Going with the Honeywell MGT22 and having Honeywell build the whole assembly was a great idea, because, Honeywell had already proven (in 60 other MGT22 variants) that they knew what they were doing - including in bigger heavier applications like Ford pickups.

So, Subies coming off the line today with Garrett's MGT22 are using pretty much the same turbo as 60 other big (Ford trucks) or expensive (BMW, Mercedes) applications. Honeywell did different exhaust plumbing, attachments, wastegate, etc... but, I suspect that the team still knew what they were doing.

I'm still digging to see if I can find similar problems with other Honeywell/Garrett MGT22's - haven't yet - but that doesn't mean they don't exist.
 

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Tangential Side Note: it's kinda interesting, but all the first run Ascent turbos are stamped "HONEYWELL" very prominently in a couple of places. All the rest will of course say "Garrett" because Honeywell spun them back off during the build of the first run Ascents (2018).

I had an Ascent owner ask me once if they had a Honeywell or a Garrett turbo. It was one of those "car is a motor vehicle, but not all motor vehicles are cars" answers. "Yes, you have a Garrett MGT22, but whether it says it was made by Honeywell or Garrett depends on if Honeywell still owned them when it was made."

Of course, it's the same MGT22, built by the same team.
 

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That's exactly what the data showed. And that's exactly how I get it to do so. Oh, doing really steep climbs and making it work at low RPMs (and then quickly letting up off the gas) will do it too.



Well, I wouldn't call it small. It's bigger than many STI and WRX turbos, and does great moving Ford F150's and various heavy luxury cars. And it's barely boosting in the Ascent. 15ish psi, maybe 16 psi on bursts before the ECU clamps it down... but it could be doing 22-24 psi (per Garrett/Honeywell).
The WRX uses the same turbo and it is small, its made to be efficient in a certain rpm range, so by definition it can't be big, big turbos flow lots of air and need lots of turbine pressure to build boost. What I mean by small is rated flow/horsepower capacity. For the Ascent and WRX the rating is 280hp, the STI VF48 is rated to 300-380 hp. So it is small in comparison, but has almost no lag. Also, Ford uses 2 of these on its truck engines not 1 that is a big difference.
 

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The WRX uses the same turbo and it is small, its made to be efficient in a certain rpm range, so by definition it can't be big, big turbos flow lots of air and need lots of turbine pressure to build boost. What I mean by small is rated flow/horsepower capacity. For the Ascent and WRX the rating is 280hp, the STI VF48 is rated to 300-380 hp. So it is small in comparison, but has almost no lag. Also, Ford uses 2 of these on its truck engines not 1 that is a big difference.
The WRX uses the IHI VF48 turbo. It's actually smaller. Pic of one below. I posted a side by side taken by another Subie friend, some place in the forums. The size difference is pretty noticeable.
  • EDIT: does the 2020 use it? The IHI VF48 is in the 2000s-2019 WRXs.
As for hp, the MGT22 has been pushed to 500 hp while staying inside Garrett's boost range, on an Ascent engine.

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