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Discussion Starter #1
Hello everyone.

New to the forum and new to the modding world. I've had my 08 impreza 2.5i since may (first car) and have been trying to learn as much as possible.

Here is a scenerio I want to run by you and hopefully you can let me know what I am doing wrong or can do differantly.


I want to purchase the SPT catback for the wrx while it's still listed at $330.00.

Now.... After I install this will I be able to throw on a stromung high flow cat. Will there be fitment issues with the 3' spt piping?

Also.. Headers. I want UEL to go along with all this....

Basically what I am trying to figure out is

A) Will all of these components fit together?
B) Do I need to install them all at the same time or can I go bit by bit?
C) If a/b are not and option then how would I go about new headers/cat/catback and what are my options?

Thanks in advance for your patience,

Jack
 

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Rallyshark is the man to talk to about NA imprezas'

he should be chiming in at any moment....
 

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well ill add my 2 cents in before the guru arrives. The Borla UEL headers and the Stromung HFC should def fit. I just got the UEL headers (the end is like 2") and im shipping them to get coated tomorrow, and my Stromung HFC arrives friday. as for the exhaust, im fairly certain the Stromung ends in 2.25", so my guess is that trying to get a donut gasket to stretch from 2.25 to 3 is gonna be tricky.

also, hopefully the headers/cat will bolt on to stock cat-back before upgrade because thats how i plan on doing it (step-wise).

hope this helps!

(btw i would say, and im sure rallyshark would too, dont bother getting the 3" SPT just because its cheap, get a custom 2.25" for less, or do what im doing and getting custom piping with a Stromung muffler (will be about $500))
 

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well ill add my 2 cents in before the guru arrives. The Borla UEL headers and the Stromung HFC should def fit. I just got the UEL headers (the end is like 2") and im shipping them to get coated tomorrow, and my Stromung HFC arrives friday. as for the exhaust, im fairly certain the Stromung ends in 2.25", so my guess is that trying to get a donut gasket to stretch from 2.25 to 3 is gonna be tricky.

also, hopefully the headers/cat will bolt on to stock cat-back before upgrade because thats how i plan on doing it (step-wise).

hope this helps!

(btw i would say, and im sure rallyshark would too, dont bother getting the 3" SPT just because its cheap, get a custom 2.25" for less, or do what im doing and getting custom piping with a Stromung muffler (will be about 0))

Cheers dude,

Are you going to run 2.25' from the stromung hfc? Is it possible to order a hfc from stromung that is 2.5'?

Interested to see how your project comes along.... Seems like I may be taking the same route if all goes well. So let's hope it does :)

Jack
 

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thanks! the Stromung only comes in 2.25" but im pretty sure you could connect it to a 2.5" midpipe. you may have to drill your own gasket holes or something i have no idea. but yeah im running custom piped 2.25" from the Stromung HFC to a Stromung dual muffler, and then ill run both exhaust pipes together past the axle, separate them, and make it look like a true dual. Basically im switching from a true dual to a false dual, but im still gonna lose backpressure overall due to 1.75" or 1.5" to 2.25". hope that helps get some ideas rolling. ill keep everyone posted with updates, but im sending the headers to shipped tomorrow to be coated so theyre gonna be ready to install in about 2 weeks.
 

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Sorry I'm so late to the party, but I come with some possibly useful news :)

First, don't buy the SPT exhaust just because it is cheap, it doesn't sound all that great and if you are looking at buying a HFC, loudness is not an issue (the SPT is really quiet), I'd recommend as battlesnake says..."get a custom midpipe and axleback piping but use a stromung muffler. My 2 cents, I think you'll be much happier with the sound of UEL, HFC, and stromung custom catback.

Second, I took some measurements of the stock 08 2.5i exhaust which I'm sure more than just the poster may be interested in... (these are all hatchback measurements...so they are probably different after you get back the midpipe resonator)
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The cat pipe has two diameters:

The pipe diameter that connects to the header side is 2 inches...the pipe diameter that connects to the midpipe is 2.5 inches
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The midpipe is also kinda interesting....it is initially 2.5 inches to mate up with the cat pipe correctly, and then within about 1/4 inch it tapers back down to 2 inches again which is the diameter of the remainder of the pipe on the exhaust.

I estimate that a 2.75 inch to 2.25 inch catback piping would properly mate to the donut gasket...and a 3 inch and 2 inch would probably work, although there might be some small amount of leakage.
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I've attached a "diagram" below to illustrate the differences between the 99-01 classic impreza and the new 08 exhaust setup. Another 3G member is correct, the 05 legacy NA header seems to be the same as the 08 2.5i header.

If Borla makes a UEL header that works on the 05 Legacy NA, I would be inclined to believe it will work on the 08 2.5i as well. A previous gen impreza UEL may work, but it takes a completely different path than the stock header does, so it's a gamble (shown below).

So to answer your questions:

A) If you can get a UEL header that will work with the 05 Legacy NA, then you can theoretically bolt up a HFC that bolts to the same header and run with it. However, you may have to modify the angle of the piping on the cat section, it is hard to say...we are blazing a new trail here :) The SPT may have trouble fitting to the 2.25 inch HFC since the stock cat is 2.5 and the 3 inch midpipe is already at the upper limit of fitting on the stock cat....so you may have to decrease the pipe diameter down to what will fit on the HFC.

B) If this was a complete bolt-on system, I'd say go bit by bit...but there are alot of wildcards and variables here...i'd say it would smart to get all the stuff and get it all modded at once. The last thing you would want to do is have to mod the exhaust once to fit...just to find out that you'll need to mod it again because the part you just got in doesn't work with the way the exhaust was previously modded.

C) I think the route you may end up having to take is the one similar to battlesnake...buy headers, buy a HFC, buy an axleback exhaust and get a shop to make all the custom pipes to connect them all.

Here is the diagram by the way.

 

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wait so the 08 headers are not the same as 06/07??? how so? do they just run to the other side of the engine or what?

and do you think the Stromung HFC will bolt on to the stock midpipe?? i have the stock donut gasket and a subaru OEM one that i think is larger i dunno...
I cannot vouch for the 06-07 Header design as I've not crawled under an 06-07 2.5i...I know the 99-03 2.5RS's share the same borla header design (which is the one I illustrated In red)

I don't have direct info on the 04-07 header design.

If you got headers that will work on an 06-07...it is likely that they'll work on the 08 although i'm just guessing.

As far as i can tell, they just exit on the other side of the centerline of the car. The exhaust ports look the same and such.

There is a video on youtube of a 2006 2.5i with borlas, so they probably bolt up fine.

What model year is the stromung HFC designed for? If it is a 99-03, then you will need to modify the pipes to mate up with the stock midpipe....although once you do your custom catback, it is no big deal obviously.
 

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heres a look from above of 06/07 headers. (in this pic the Borlas will run to the right instead of left)

http://i131.photobucket.com/albums/p306/ZeppelinPie792/UEL faq pics/Copyofexhaust001.jpg

this guy was able to bolt on UELs so ours should be fine.
I would agree then...UELs made by borla should have no problem fitting the 08 then...

It is important to note that borla has only made headers for the 99-03 impreza RS and they are the same design for all these models years (if the pictures on the borla website are correct)...therefore, you can probably buy a borla header made for any NA impreza (that has dual exhaust ports on both sides) and fit it on an 08.

Using the above info, the stromung high-flow cat should bolt up directly to the borla headers...you will probably only need to modify your midpipe to fit correctly to the HFC, add an 02 sensor extension, and maybe using the mechanical defouler mod (rallitek also sells a spacer) to prevent CELs.

Great research battlesnake, +1
 

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rallyshark/battlesnake+1 you guys both obviously have a wealth of knowlege reguarding us n/a 2.5s and i for one appreciate it!
let me pose this question would i gain any volume/power by installing a wrx stock exhaust on my 2.5i sedan?
 

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rallyshark/battlesnake+1 you guys both obviously have a wealth of knowlege reguarding us n/a 2.5s and i for one appreciate it!
let me pose this question would i gain any volume/power by installing a wrx stock exhaust on my 2.5i sedan?
Thanks chad, we do our best. I view it as a fun challenge to figure out exactly how to make it work.

By the "stock exhaust" I assume you are referring to the catback (midpipe and muffler sections).

The WRX sedan catback should bolt up directly to the 2.5i sedan....I think it is a slightly larger diameter though.

Would you gain power? If it is indeed a slightly larger diameter pipe, then maybe a little bit of power in the mid to higher RPM range, however, you will probably lose some of your lower RPM power.

This low RPM loss will be due to less back-pressure...subaru configures the 2.5i from the factory to have good low to mid range which is what most drivers want. More mid to high RPM power can be more beneficial for racing...however the power that you gain from just switching a catback will be minimal. On a subaru NA car, swapping the catback is mostly for looks and sound.

If you are talking about the header or cat section, the header will at least need to be modded, maybe the cat section too.
 

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i was referring to the cat back section i am not looking for huge power gains if really any just a little bit of sound really but i may just go to my local muffler shop and see what they can do i dont want two coffee cans hanging out the back of the car i would just like a little bit of volue and some power is all i really expect
 

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always trust the rallyshark :)

but actually assuming the stock WRX catback is 2.5" i dont think you'd see too much loss in low end torque. it wouldnt sound as nice as an aftermarket muffler with 2.25" piping, but its an idea. anything bigger than 2.5" and youll be dissapointed. thats why im not gonna get the 3" SPT, which isnt even that nice sounding anyway (sorry to bash)
 

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i was referring to the cat back section i am not looking for huge power gains if really any just a little bit of sound really but i may just go to my local muffler shop and see what they can do i dont want two coffee cans hanging out the back of the car i would just like a little bit of volue and some power is all i really expect
Your local muffler shop can probably do it for less money than a bolt-on prefab catback.

If you get 2.25 to 2.5 inches from the muffler shop, that will probably be a good diameter, although don't go larger than 2.5 as you'll notice some low end torque loss.

I can't vouch for the sound of a muffler shop's stock mufflers, I guess it depends on the shop.

I've found the stromung has the best NA sound in my opinion, but other muffler brands certainly don't sound bad unless you get a REALLY cheap muffler and then you'll sound like a beefy civic ;) I've heard some people use flowmasters or generic glasspacks...although I have no idea about which models.
 

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Hi guys. I have a quick question. I am new to the subaru scene and a 2008 impreza 2.5i was handed down to me. I'm loving the car so far and have done some suspension mods already. Myself coming from the Honda scene, i'm still new to the Subary scene. I have been reading everyone's responses regarding the UEL headers for the 08 2.5i's and i was looking into it further and comparing photo's etc... I noticed nobody mentioned anything about the Oil filter clearance? Will any of NA headers (Borla or replica's) block access to the oil filter? I really want to do this mod and would like to hear more of the boxer sound without scrificing performance. This car is perfect for a daily commute.
 

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battlesnake already has his borlas on his 08 2.5i, PM him and report back here with the answer about the oil filter.

It looks like it may, but maybe not.

It's hard to perfectly line up reference photos due to perspective and scaling.

This is a good question.
 

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I didnt do the install myself but from what i hear it just makes it hard to fit you fingers in on the header side. But the headers really just go around it so getting it out should not be a major issue, if anything you might need one of those oil filter rubber tong things to grip it but probably not.

Actually the guy said that theres plenty of room with the swaybar too which is awesome and i wasnt expecting :)

as a side note to badpmpnoy, youre probably going to have to install a HFC with it, and then you need to rotate and extend the mid-pipe. If i were you, i would install the cat-back you want on your car at the same tims so you only have to pay for all the welding once. just a tip. oh and in terms of sound, youre still not gonna really hear your exhaust, even with a HFC. That huge resonator and those two huge mufflers (or one in a hatch) really do a number to any exhaust noise. you will hear a louder engine, but you will also hear a lot of ticking from the engine, because the headers are so thin. Mine are coated, and im still wondering if i should have wrapped them. The thing is you have to live with it until you get any kind of cat-back, at which point the exhaust gets louder than the ticking, and joy ensues.
 
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