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2017 - STi exhaust on FA20 - NOT recommended!

('14-'18) 
24K views 41 replies 16 participants last post by  16fxt_van 
#1 ·
Hi people, im not sure in anyone here has done it but i went ahead, after a techy recommended it, and installed an STi exhaust on my Forester 2.0XT 2017. Here is my verdict:

1. Fuel efficiency sucks now
2. Sound is awesome but droning is pretty annoying
3. The CVT has a weird jitter.

I talk to Crawford Performance (they have nothing to do with this. I simply have good contact with them from other activities) and they said this should happen. Im now swapping to the stock exhaust and see what happens.

All back to normal...Mileage great again and torque is back. The awesome sound is gone. Bottom line, the STi Performance exhaust does not work for any vehicle equipped with an FA20 engines.

M FXT has the new 2.0 turbo and is not as torquie as the EJ25...That why maybe you did not notice any issues.
Final Verdict For now: NOT RECOMMENDED.


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#2 ·
I will be interested in your results with the standard exhaust. I have a '15 and installed a '15 STI exhaust a couple of years ago. I did not notice a mileage reduction but did have the drone. It was really bad at low speed in I mode.

You can remove the drone by blocking or partially blocking one of two muffler outlets. There is a resonance and disupting the sound from one on each muffler will remove the drone. I reduced the area of the outer 2 pipes and the drone has gone. I think that, unless one is racing the Forester, the open 2 pipes will flow well enough. It is an exhaust system for a 2.5 l engine, the pipes are slightly larger and also have smoother bends
so I cannot see that my reduction of outlet area would make any difference. And I have seen no change in mileage or driveability.

There may be some differences in your '17 so my experience may not apply.
 
#6 ·
All back to normal...Mileage great again and torque is back. The awesome sound is gone. Bottom line, the STi Performance exhaust does not work for any vehicle equipped with an FA20 engines. M FXT has the new 2.0 turbo and is not as torquie as the EJ25...That why maybe you did not notice any issues.



This is my city reading 10km/L I was at 5km/L...Big difference.



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#7 ·
It is strange that you saw so much difference in mileage. On my 2015 XT I have the 2015 STI OEM exhaust cat back with 4 outlet pipes and average around 8.2 l/100 km (12 km/l) overall city and highway.
That is using S# almost all of the time running regular (87 AKI) gas. The mileage does drop in the Winter with cold starts and lower temperatures.

So very little if any change in gas mileage for me with the STI exhaust. Were there any other changes made?
 
#9 ·
Backpressure wouldn't cause this big a change in mileage. Not sure what did it, but suspect your car is just setup or tuned a bit differently then normal. Perhaps if you also ran a Cobb Stg 1 map you would see more normal numbers (not that it's needed when just doing catback exhaust).
 
#10 ·
No idea, i have done many bolt on upgrades to several of my cars but never have i had such a noticeable increase in consumption. Very odd. But im sure it has to do with the back pressure as well. Never did I think the exhaust would also screw with the CVT algorithms but apparently it did.


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#13 ·
The best way I can describe it is I only got 250 to 350kms from a full tank combined and and my Infiniti Fx35 gives me 500km combined being a V6 with 305bhp. Its my first experience with Subaru and I cant say its been the best. The dealer hates me because I have honestly been a nag about this but hey, they recommended the STi exhaust from the get go and said it would not hurt the warranty...Of course I said yes....because I wanted a invidia or a nameless catback "designed for the FA20" and they said it would screw my warranty up... So, I went ahead with the STi.
I have heard in other forums about the CVT acting up though...You feel the jitters much more with a free exhaust i suppose and it gets annoying. Its my first and last CVT thats for sure.
Im 46 yrs old and I have had several Jeeps from Sahara to Rubicon's, Infiniti, Corvette, Honda Si, Mazda, VW GTi, Suzuki Swift GTi and I so wanted a Subaru but its been a bitter sweet experience so far.


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#14 ·
Wait a second here. I'm not sure what's happening to your car, but there's absolutely nothing wrong with running the STI performance exhaust on the FA20. Check the WRX option sheet, it's listed right there as an option. Highly doubt Subaru would offer it as an option on an FA20 car if it did the things you are describing. I've had that exhaust on my XT for over 15,000 miles without any issues, OR any loss in fuel consumption. I ran this both on the stock tune and now on the Cobb Stage 1 OTS. I'm going to guess that you either had an extremely horrible leak going on, or some other issue.

 
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#15 ·
Wait a second here. I'm not sure what's happening to your car, but there's absolutely nothing wrong with running the STI performance exhaust on the FA20. Check the WRX option sheet, it's listed right there as an option. Highly doubt Subaru would offer it as an option on an FA20 car if it did the things you are describing. I've had that exhaust on my XT for over 15,000 miles without any issues, OR any loss in fuel consumption. I ran this both on the stock tune and now on the Cobb Stage 1 OTS. I'm going to guess that you either had an extremely horrible leak going on, or some other issue.
Are you running a CVT or manual?


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#19 ·
True. Well, I honestly do not know what went wrong but bottom line is that consumption is back to normal. I did ask the dealer and they said that they sales guy did offer the STi P Exhaust when he should have offered the WRX P exhaust but they did not have have the WRX P exhaust in stock. They do offer both P exhausts but one for WRX and one for STi. Im putting up the options sheet.




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#18 ·
I don't see how that could have happened. You have to have had something else going on. Perhaps a bad batch of gas, etc. There's no situation where any catback exhaust should impact your fuel economy that much. A catback is a catback, no matter who makes it. If it was the catback that was causing your issue, you're going to have the exact same issue with an Invidia or Nameless exhaust as well. They are all just pipes, nothing fancy about them.
 
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#20 ·
Only difference between the two is the resonator. Since the stock STI doesn't have resonators in the downpipe, they add one in the midpipe. Meaning that that one would be a bit quieter on your car than the WRX one, but that wouldn't impact your fuel consumption like that. For what it's worth, I do have the one without the resonator on my car. But I'm sure you saw that enormous resonator on your stock midpipe. I'd highly doubt a higher-flow resonator like the one on the STI version would affect performance in any way.
 
#21 ·
Yes, i did see it. But like I said, i wanted a better sound and i got it but at a huge difference in fuel economy. You're in florida and im in panama city, panama at sea level so i assume there would be no difference btw your car and mine. It could be that im missing the stage one tune....How long did you drive the car with the STi Exhaust on the stock tune?


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#24 ·
No, the dealer did. But I have installed other exhaust in other cars with no issues. I honestly don't get it. Im asking Crawford Performance for help because I don't want a Soccer Mom car...I want a Soccer Dad car...The sound is so cool! Does increase performance but it did sound great. Bummer!


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#23 ·
there seems to be something else going on here... (I am not calling @DannyPTY a liar, just hypothesizing on root cause)

fuel economy isn't impacted as much unless there is a LOT of restriction... the new exhaust has less restriction than the stock... performance (the ability for your car to 'exhale') is impacted by restriction...

this sounds like bad gas (like 87 being put in when it needed 91+)
 
#25 · (Edited)
STi EXHAUST ON FA20 Forester





We have 95+ here and also 109 so fuel is not the problem. If it would have been fuel I would still have an issue. I am using the stock exhaust and the car is back to normal...Im just sharing my experience. Not that some one said he said. It's a mystery to me as well.


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#26 ·
I am at a complete loss... unless somehow the exhaust flow was restricted... you should (based on my research on the interwebs) only see an impact of a few percentage points on your overall mileage...

for now, it seems like you are back to a good place....
 
#27 ·
Yep...Since the STi P exhaust only gives the car a great sound but no performance at all im going for an axle back unit that will not kill the bottom end too much. I will be installing the Crawford Performance Eco-Block and the K&N in box filter in about 10 minutes as well.
Let's be honest if I want a race car I guess I have to get one....This is my daily driver with a pinch pf umpf. Fuel economy is a priority.


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#32 ·
You'll have to cut your bumper to fit the quad tips, but any catback exhaust for the 2015-2017 WRX or STI will fit on a 2014-2016 XT. I'm not 100% on the fitment on newer models. Subaru likes to rotate flanges during mid-cycle refreshes to annoy people.
 
#36 ·
Hi people, im not sure in anyone here has done it but i went ahead, after a techy recommended it, and installed an STi exhaust on my Forester 2.0XT 2017. Here is my verdict:

1. Fuel efficiency sucks now
2. Sound is awesome but droning is pretty annoying
3. The CVT has a weird jitter.

I talk to Crawford Performance (they have nothing to do with this. I simply have good contact with them from other activities) and they said this should happen. Im now swapping to the stock exhaust and see what happens.

All back to normal...Mileage great again and torque is back. The awesome sound is gone. Bottom line, the STi Performance exhaust does not work for any vehicle equipped with an FA20 engines.

M FXT has the new 2.0 turbo and is not as torquie as the EJ25...That why maybe you did not notice any issues.
Final Verdict For now: NOT RECOMMENDED.


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I speak from experience. I had this exact same issue when I removed the stock mid-pipe and mufflers; and went to a Stock WRX and Namless single tip 5 inch mufflers. car felt down on power and loss of torque. boost would not go above 15 psig. CVT acting very weird too. one morning the battery died over night (unrelated to the exhaust and still dont know why, NO DOME LIGHTS ON). so I had to charge it an put in through the Throttle relearn procedure. what a difference but not back to normal yet. I also hated the drone, because there is no resonator in the stock WRX mid-pipe. so i switched out to the STI stock midpipe. big difference!!!! sounded much better still keeping the same Nameless 5 inch mufflers. I had the car stall and i brought it in to subaru to have everything checked out, i also discussed the drive-ability issues i have had been having. The tech decided to update the ECU and TCU with an update that was part of a TSB (the costumer has to complain of a drive-ability issue for this to happen or else they do not do it). they look through the multiple updates and pick one that matches correcting the issues and symptoms that you discuss with the service writer and/or tech. after the update and driving the car like hell for a week, boom all corrected. now the car actually feels like it has more acceleration at high speeds, then when stock.

I think your problem stems from not:
1) doing a throttle body relearn procedure afterward
2) having the dealer reflash the ECU and TCU with updated programming

I am still running the STI stock exhaust with the Nameless 5 inch mufflers, no modifications needed. I suggest getting the genuine subaru exhaust crush gaskets for the mid-pipe to the muffler. NO RTV, just a lite brushing of never seize.



there seems to be something else going on here... (I am not calling @DannyPTY a liar, just hypothesizing on root cause)

fuel economy isn't impacted as much unless there is a LOT of restriction... the new exhaust has less restriction than the stock... performance (the ability for your car to 'exhale') is impacted by restriction...

this sounds like bad gas (like 87 being put in when it needed 91+)
and

There's probably a difference in back pressure between the 2.5 STI motor and 2.0 Forester, perhaps this is what has caused the difference. While a car can benefit from a free flowing exhaust, it does need a certain amount of back pressure.
the turbo is the largest exhaust restriction and in my eyes sets stage for any necessary back pressure, but a larger exhaust flows better, pressure is different from flow.

please read this below @DannyPTY

to be quite honest i think it has more to do with the mid-pipe resonator being removed. the stock Forester XT 14-18 has one in the mid-pipe. the WRX stock does not. the WRX performance STI/SPT exhaust does not have a resonator either. BUT

The WRX STI performance STI/SPT exhaust does have a resonator.

I know the FA20DIT engine from 2017 and up is part for part shared with the WRX and Forester XT. minus the exhaust valve springs. yes i went through every part and compared part numbers on the long block of both cars. the only difference is the exhaust valve springs.
So one would think exhaust from WRX should be fine with Forester XT. FA20DIT butt buddies.

But i think Subaru put the stock resonator in the Forester XT mid-pipe for a reason, and when it is removed while trying to keep a stock tune the ECU does not like it. I suggest @DannyPTY tell the dealer that install this part that they should have recommended the SPT performance exhaust for the STI. and since the dealer know that the exhaust


All back to normal...Milage great again and torque is back. The awesome sound is gone. Bottom line, the STi Performance exhaust does not work for any vehicle equipped with an FA20 engines. M FXT has the new 2.0 turbo and is not as torquie as the EJ25...That why maybe you did not notice any issues.


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I cry for you. it is not your fault, especially since the dealer installed this stuff and advised you on it.

I would put the ball in the dealers court. what did they say when you complained?

-find a used STI SPT performance exhaust
-put it on your self
-bring it to the dealer and discuss the same drive-ability concerns you have told us here.
-dont leave until they update the ECU and/or TCU. the update i got that helped me was "customers with complaints of bad rear wheel traction around turns". tell them that and i hope all works out.
you can have the fun dad car!!!!!
 
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