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Discussion Starter · #1 ·
Just picked up an Ascent for my wife. Got to looking underneath it, and am shocked at how small the exhaust diameter is after the Y-pipe (leading up towards the mufflers). Looks to be maybe 1 3/4" max. Being turbocharged and all, seems like it'd benefit from something a little less restrictive. Is there some rationale I'm missing there???
 

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Just picked up an Ascent for my wife. Got to looking underneath it, and am shocked at how small the exhaust diameter is after the Y-pipe (leading up towards the mufflers). Looks to be maybe 1 3/4" max. Being turbocharged and all, seems like it'd benefit from something a little less restrictive. Is there some rationale I'm missing there???
You don't need it. The 2.4 would never need anything larger unless the j-pipe (the exhaust outlet after the turbo) were to get changed the motor tuned. Take the 2.5 STI or the 2.0 WRX, the only thing changing the rear cans do is make you louder, that's it. They need to change the j-pipe or the downpipe (in the 2.5) and the midpipe and get a tune also to gain any more power. The current restriction is the j-pipe and the mid-pipe getting to the split.
 

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I thought I was the only one that saw this. To me it looks like there is many different diameters on piping connecting to eachother. When you step on the ascent it has a decent growl to it. I can only imagine what a full exhaust system would sound like. An axleback might sound really good this car.
 

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To get really good sound out of an engine (and this is subjective...but i really like it) is a full 3" turbo-back exhaust with no cats or resonators and minimal sound attenuation from muffler. Gives it a little rasp and a lot of volume. I can't imagine it would be pleasant in an Ascent though. The drone would be horrendous without the cats and resonator.
 

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Just picked up an Ascent for my wife. Got to looking underneath it, and am shocked at how small the exhaust diameter is after the Y-pipe (leading up towards the mufflers). Looks to be maybe 1 3/4" max. Being turbocharged and all, seems like it'd benefit from something a little less restrictive. Is there some rationale I'm missing there???
What's the diameter of the two pipes at a header?
 

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Discussion Starter · #6 ·
I thought I was the only one that saw this. To me it looks like there is many different diameters on piping connecting to eachother. When you step on the ascent it has a decent growl to it. I can only imagine what a full exhaust system would sound like. An axleback might sound really good this car.
Yeah the pipe diameter is definitely all over the place depending on where you look. I'm sure Subaru put a ton of R/D into it though, my best guess is they had to restrict it (pipe diameter) a bit to get their torque rating low in the RPM range. For a 4600lb vehicle, I already feel like it's pretty quick; but, I'd really love to see what untapped potential these things have when released w/ a tune and better flowing exhaust.
 

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Yeah the pipe diameter is definitely all over the place depending on where you look. I'm sure Subaru put a ton of R/D into it though, my best guess is they had to restrict it (pipe diameter) a bit to get their torque rating low in the RPM range. For a 4600lb vehicle, I already feel like it's pretty quick; but, I'd really love to see what untapped potential these things have when released w/ a tune and better flowing exhaust.
Yes I believe you are right. To keep the torque down low they had to probably make some parts undersized to create velocity which helps low end torque. Im sure alot of R/D went into it and I do like how quick it feels down low. Thats why I probably would only do an axleback for sound. A full 3inch catback might lose torque down low but gain alot up top, but then that means you'd have to race your car everyday to even take advantage.
 

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Yes I believe you are right. To keep the torque down low they had to probably make some parts undersized to create velocity which helps low end torque. Im sure alot of R/D went into it and I do like how quick it feels down low. Thats why I probably would only do an axleback for sound. A full 3inch catback might lose torque down low but gain alot up top, but then that means you'd have to race your car everyday to even take advantage.
well, no, it wouldn't really matter until you increased the size of the downpipe, which will require a retune, which would probably net you both torque and HP across the board. Exhaust velocity -really- matters pre-turbine. After it gets through the turbine, you want to let the exhaust get out as easily as possible. A dyno might show some sort of net increase/decrease...but probably not outside the change you'd see from 80 vs 90 degree temperatures. Increase in piping diameter post catalytic converter won't do a whole lot, because the cat is the big restriction in the system. Removing the catalytic converter and/or going to a full TBE with increase diameter will be where power and torque increase. Increasing the diameter of the primaries in the exhaust manifold or the up-pipe diameter can decrease performance but you still want them to be able to flow enough to minimize backpressure and prevent reversion (exhaust gases flowing backward into the combustion chamber in the overlap period). Backpressure is force applied against the piston which results in lost power.

Of course, there are situations where not all of this is accurate...but in general, you want exhaust velocity pre-turbo, and flow post turbo...but changes typically require a re-tune of the ECU.

I realize that some of the terminology here isn't necessarily in line with the ascent (downpipe/up-pipe) but the concept is the same. The everything between the exhaust port and the turbine housing are what generate all the back pressure in a turbo system. Anything after that should be free flowing to allow the exhaust to vent and reduce load on the turbine. Any excess pressure in the system works against the ability of the turbine to spin.
 

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well, no, it wouldn't really matter until you increased the size of the downpipe, which will require a retune, which would probably net you both torque and HP across the board.
Yes, exactly. And technically, this is a j-pipe. A downpipe is technically for the 2.5HT EJ motors. The turbo is mounted high and the main exhaust is a down-pipe. With the lower mounted snail, the exhaust is a different configuration. I commented early in this thread, Subi Engineers have the system right. They have a flat torque curve, they have a CVT and they have no drone. If people start messing with this system and they don't engineer the whole thing ... sh*t will happen. Drone, torque loss, fart-noises...

If COBB is working a tune to deliver through the AP ... they will be working on a full system for Stage2 if there is any benefit. My guess is they might make a J-pipe. Same goes for Perrin or GrimmSpeed. But this is my conjecture. Untill there is a big demand for tuning. I doubt it.

This is from a developer of Subaru Performance Parts. BTW, thank you all interest. Sway Bar Bushings are flying off the shelves.
 

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Yes, exactly. And technically, this is a j-pipe. A downpipe is technically for the 2.5HT EJ motors. The turbo is mounted high and the main exhaust is a down-pipe. With the lower mounted snail, the exhaust is a different configuration. I commented early in this thread, Subi Engineers have the system right. They have a flat torque curve, they have a CVT and they have no drone. If people start messing with this system and they don't engineer the whole thing ... sh*t will happen. Drone, torque loss, fart-noises...

If COBB is working a tune to deliver through the AP ... they will be working on a full system for Stage2 if there is any benefit. My guess is they might make a J-pipe. Same goes for Perrin or GrimmSpeed. But this is my conjecture. Untill there is a big demand for tuning. I doubt it.

This is from a developer of Subaru Performance Parts. BTW, thank you all interest. Sway Bar Bushings are flying off the shelves.
can you post a link for your bushings. Im thinking about getting one.
 

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