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2015 WRX STI
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Discussion Starter · #1 ·
Hello to all,

I am sure I am beating a dead horse here, but I am new and never really been on any forums at all. So I am not familiar with it. I just need some help and I am hoping that the subi family is a good one to belong to. My son got me into these vehicles so I am older but enjoy the hell out of the sound and horsepower. Just a fun car to drive. Anyways, here goes nothing.

I got really lucky and got a 2015 STI with a blown motor for next to nothing. It appeared that a kid had it, and cratered cylinder 4. I know it is not everyday you can start with a car without a motor in it. I can get the mods first and add them when installing the motor. I get to start from scratch

I am re-building the car, and everything is all there except the motor. I have purchased a new motor (2016 STI) with only 30K miles on it. I have done a little research and from what I can find the car can be finicky at times depending upon the mods. So what I have chosen to do so far before putting the new motor in is add the 1. IAG Air-Oil Separator 2. Cylinder 4 Mod 3. Mishimoto 2 core radiator 4. Perrin Pitch Stop Mount. For fun I added 5. Kartboy short throw shifter. These have all been purchased before I have even put the motor in the car. I am looking for reliability and I am trying to create that now with the new motor before adding any other mods. This will be a daily driver for me, so I am not trying to go wild on horsepower. Like I said before, I got lucky, REALLY lucky.

Now that the engine is going in the car in the next few days, I know that I am going to need a new exhaust. Well shit! More money!!! So before I just buy a STI factory exhaust, I am trying to find out if I can put on a turbo back exhaust (TBE) without getting a tune. After all, If I am starting from scratch and have to buy a complete exhaust, I might as well find out if I am going to need a tune if I do that. I am not ready for tuning. So If I am going to need a tune, I will just go with a stock STI exhaust. Theoretically, if I keep everything stock, it is plug and play. Please keep in mind I have the stock ECU and the motor is all stock besides what I have already purchased and adding to the car when the motor goes in, which I know does not require any tuning.

I am considering the Invidia Gemini R400 quad with tips. I am wide open and all ears to any and all suggestions for an alternate exhaust with a little more sound. (Love that STI sound) My biggest thing is regarding the tune for the vehicle if I were to purchase a TBE. WILL I NEED ONE???

Again, I apologize for all of this, I am new, and not very familiar with forums. Thank you to anyone for your input.
 

· Not a mod... or is he? Or, is he not?
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15,756 Posts
You can't put a turbo back on without a tune. Companies willing to do the tuning are dwindling. Rumors say Cobb has something in the works with an EPA legal exhaust. Until then. I'd use the OEM downpipe and go with a cat back.

The cyl mod is snake oil as far as I'm concerned. There isn't research that says it's effective. It also can't solve the uneven cylinder temperature issue caused by the unequal length headers. So it's like putting a tiny band aid onto a bone deep chainsaw wound.
 

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2015 WRX STI
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5 Posts
Discussion Starter · #3 ·
You can't put a turbo back on without a tune. Companies willing to do the tuning are dwindling. Rumors say Cobb has something in the works with an EPA legal exhaust. Until then. I'd use the OEM downpipe and go with a cat back.

The cyl mod is snake oil as far as I'm concerned. There isn't research that says it's effective. It also can't solve the uneven cylinder temperature issue caused by the unequal length headers. So it's like putting a tiny band aid onto a bone deep chainsaw wound.

Thank you so much for your response. It is good to hear what sti owners have to say and have experienced. Again thanks for the response.

Next question is where can I get a down pipe to include the upper and lower, and it be stock. Are people on this blog selling them???
 

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Based on years of reading on these threads, IF I was going to mod an STI for best bang for my buck, while keeping the car reliable, here's the route I would go:

Killer B equal length header. This will remedy the uneven temperatures.
Catted down pipe
catback exhaust (the quieter the better, because the car will be much louder)
Cobb Accessport tuned by the best possible tuner I could find, focusing on realiable safe tunes.

I can't remember if an upgraded intercooler is needed for this setup, but I've seen some reviews and people love it. It's said that the power comes on quicker and remains strong throughout the remainder of the rev range. It seems to make the most sense. Don't nickel and dime other crap. Stick to the basics.

As far as the AOS, it seems like you never saw them much until recently, relatively speaking... Now I see them all over the place since they started making them look cool in all kinds of neat colors. I should probably do more homework, but that tells me a lot. I say just treat the car with respect and that might remedy needing an AOS.
 

· Not a mod... or is he? Or, is he not?
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15,756 Posts
There are times and places for air oil separators, often times they are more of a bandaid for an ego or an engine problem. The more research I've done on the topic leads me to the conclusion that in a system where egr is at play one could increase effective knock resistance of the fuel charge.

Otherwise if you have a situation where you are blowing enough oil to need one there may be a problem. Some performance engines excluded as fits tend to be on the more generous side allowing some blow by while not at temp.

Intercoolers should work without a specific tune, but you'll not make use of the heat exchangers efficiency.

The STI becomes fuel limited at either an intake, or turbo back in the VA chassis. The GR you limited after an intake and turbo back. These are all considerations you need to take to task before going down a rabbit hole of sadness.

I don't know who has OEM downpipes. You may have to hunt down a used one, or as mentioned earlier find a shop with the not my problem attitude to tune it. Just be aware if the shop comes under EPA scrutiny so will you.
 

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2015 WRX STI
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Discussion Starter · #6 ·
ProZach626. Thank you for your input especially with the Air/Oil Separator and the equal length tube headers. I was not aware of the equal length header situation regarding the heat. Very valuable information. X-Man, I really appreciate the comment about the band aid for an ego. That is awesome. I appreciate both of you providing valuable information and experience. As far as the Air/Oil Separator, I am going to put it onto the car. I will be treating it with respect, but I will be running through the gears from time to time and have fun with the performance, but I am not trying to kill the car. The previous owner did that as I stated in my first post. All I am trying to do is ensure the efficiency of the vehicle. From reading from both of you, the car may not need it, but it definitely is not going to hurt it. Maybe more precautionary than anything. Thank you guys so much for responding. Hope to see you guys out there some day.
 
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