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Discussion Starter #1
right, i am having a 2.25 inch cat back and exhaust made up for my 2.ltr

just want to know if there are any sensors i have to worry about and if this would be the optimum size.

also, would going from the cat back be a waste? i plan to install a hi flow airfilter, but cannot find an ecu in oz and more importantly some one who will tune it for me.

so i really am limited to exhaust and air filter.

what you all think?

btw, it will be made in stainless steel.
 

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Optimum for power, you should be lookin at 3". But no matter how big ur pipes are, just go for a tune. That should optimise your car.
 

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2.25 sounds like a good size for n/a, youll want to keep some backpressure becasue its na, biggest id say to do is 2.5.
 

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Back pressure is a debateable subject but I can tell you that on my 95 T/A and 96 SHO Taurus both with V-8 I went with 3" exhaust. Seemed to lose a little bottom end torque but openned up the top end a little more. You shouldn't need a tune with a CBE or CAI with an N/A engine. As for sensors they should be probably between the first and second cat if it is anything like the WRX. But I would bet that there are no sensors past the cat where you would start a CBE.

Seth
 

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Well, with a V8 you can go 3", with a four cycl you can't. Go with a 2.5", any bigger and your motor won't be effective in pushing out the exhaust. As far as sensors go, if you can get a look under there, see if there are any sensors. They will most likely be near the cat.
 

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Point taken Coop. I still haven't seen any good arguments about the advantage of backpressure in modern piston engines. Consider that Suby engines are used in aircraft applications with straight pipes off the manifold and no back pressure there. Plus if you are worried about back pressure the cats will certainly produce some.

Seth
 

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I have seen the planes too, but what size piping are they using? I doubt that it is 3", plus the motors are built differently, internally.
 

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Discussion Starter #8
thanks for the info guys,

after talking with alot of guys in the exhaust area around sydney australia for n/a subarus, iv found that everyone says 2.25 is the optimum size.

im thinking of having it installed this weekend if i get a chance. will post up some pics when it all done- cant wait!

now just gota find a hi flow panel locally :)
 

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Oh yeah... I forgot that you have the 2.0L, then the 2.25" would be good. For some reason I was thinking that you have the 2.5L
 

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I forget that they are 2.0 too. Does it make as much HP as the 2.5 does here? I am not sure as far as exhaust size on the planes. I am sure it isn't 3" as weight is a factor in everything in a plane.

Seth
 

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I know you are getting alot of conflicting info but:

2.25 is optimum for the 2.5L NA engine....the NASIOCers and myself from trying it out personally all think so...

I'd imagine 2.0 to 2.25" exhaust should be in the range for the 2.0L engine...backpressure is a big deal with a small NA engine...you have to get just the right balance for optimal power.
 

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Hey shark just a question here for my own knowledge. What exactly is the back pressure good for? What does it do to the engine as opposed to one with little or no back pressure? Thanks.

Seth
 

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Discussion Starter #13
well my car makes 110kws at the rear wheel, but as much torque as last years 2.5 if that makes anysense.

good tip on thinking it is a 2.5, maybe i should keep the stock catback and just get a muffler as im pretty sure the oem one is 2 inchs.
 

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Hey shark just a question here for my own knowledge. What exactly is the back pressure good for? What does it do to the engine as opposed to one with little or no back pressure? Thanks.

Seth
The question of backpressure is a tricky one because there is alot of conjecture as to what actually causes an engine to have too little backpressure. (i've found that opinions on this are widespread, some of them ludicrous). I personally don't know the correct answer either and your online research is just as good as mine.

However, the results are easily seen and documented across many engine types.

The first thing to note is that NA engines and Turbo engines are somewhat different in regards to backpressure.
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A turbo car's powerband is smoothed out and more efficient with less backpressure as compared to an NA vehicle (a more extreme example is a turbo car with an electronic cutout on a downpipe...aka, the downpipe just vents directly to the air bypassing pretty much the entire exhaust)

Top end dramatically increases with a cutout...I have a friend with an evo and the thing is crazy smooth when he opens the cutout (albeit this is top end power and he probably loses some low end torque, but the top end makes up for it.)
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In a non-turbo car, no backpressure causes a large loss in low-end torque, although lack of backpressure WILL increase horsepower up in the high rpm range.

So, logically, some backpressure is good to maintain low-end torque and a more free flowing exhaust is good for more horsepower in the high rpm range. Thus you need a good balance to get a desired result.

Good acceleration performance for a car is based upon a good power and torque curve. Who cares if your NA engine tops out at 200 hp at the 6250 rpm redline if you don't get any power delivery until 4700 rpm....the car will be slow.

I think you guys get my point, I won't beat the dead horse any longer :p
 

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I know you are getting alot of conflicting info but:

2.25 is optimum for the 2.5L NA engine....the NASIOCers and myself from trying it out personally all think so...

I'd imagine 2.0 to 2.25" exhaust should be in the range for the 2.0L engine...backpressure is a big deal with a small NA engine...you have to get just the right balance for optimal power.
hello again
I'm changing just my muffler with HKS Legamax premium. Again I'm using a 2.0L N/A 08 Impreza. would you think I will still need to change my midpipe?
 

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No you don't need to change your mid pipe to put a new muffler on it.

Seth
 

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Discussion Starter #19
hokay,

so i went to the muffler shop, in a bad mood and with my girlfriend.

i took the day of work- planned to get the rims on by 10, be at the muffler shop by 11.

so the wheel shop i was going to screws me over, big. he says he opens on saturdays, but he never showed and the shop was closed. grrr.

got to exhaust place late.

massive wait for them- over 2 hours before my car went on the rack.

then they tell me if i want to keep my mid pipe- which i do, that they will have to make a flanges and because they havent done this subaru before - they will have to make up an exhaust.

grrrr. my mrs was there getting the shits, i already had the shits, so i just said wack a muffler on.

because of all the cars they had there and how busy it was, it took another 2 hours!!!!!!!!!! like omg!

but, i got the muffler fitted. went to dinner, saw a movie and calmed down.

opinions. i went for a small almost hot dog style muffler- the reason i didnt go any smaller is that it became raspy and unplesent.

the sound is okay, but nothing spectacular and deffinatly no boxer rumbler. however the sound is there and is much better than
stock.

for a bit of noise, nice deep and no drone, it is very good, and althought i cant tell a difference powerwise, it defintaly sounds healthier uptop of the rev range.

also, the stock muffler is heavy as. you wont beleive how big it is. its huge!

i have pics but am sooo tired, so il post 2moro after some sleep.

those looking for a cheap way to sound up their ride, this is good, but a cat back is definatly needed as there is a middle resinator muffler thing that is further making it more quiet. i.e not good.

going to have the mide pipe replaced next week.

btw, since there was no difference in weight from mild steel, to stainless steel ( if anything stainless was heavier ) i decided mild steel since it comes with a 2 year warranty. and i figured if a cheve that was getting a full system done in mild steel could be good ( was a drag/ steet car ) then i guess its good enougn for my subi.

my 2 cents.

btw, dose an exhaust take time to get run in? i.e will it sound better after time?
 

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btw, dose an exhaust take time to get run in? i.e will it sound better after time?
no the exhaust doesn't need time to run in. the only change in sound is probably caused by carbon build up especially if you run catless. but its almost negligible unless you're extremely sensitive.
 
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