should i change exhaust systems?

[evolegacy]

currently I have borla headers, magnaflow cat and magnaflow muffler on a 2.5" pipe setup. The sound is great but I have a lot of back pressure when driving 45+mph, and I've already gone thru 2 sets of exhaust manifold gaskets from the pressure. I wanna change to something with less back pressure but still retain that boxer rumble that we all love. I was looking at the stromung setup and it seems decent, but does anyone know a good setup that not only gives a better exhaust flow, but improves on performance and keeps the boxer rumble?

[aznguy0087]

you can always go 3'? that would help with the back pressure!

[Plays_with_Toys]

Ummm... you know you need some constriction to actually get any exhaust velocity right? Think about a garden hose, it flows faster the tighter you have the end. It's a matter of balancing the speed with not making the engine work too hard to push the flow out, but quite frankly, you'd have to have a very extensive mod list to really demonstrate the need for a 2.5" exhaust, much less a 3". Remember, your car isn't turboed...

[rougeben83]

What gaskets are you using? It would be very hard to break a metal gasket. Youre not having gasket issues because you have "too much backpressure". 2.5" is the limit (some say even too big) for even a cammed n/a ej25. Hell people have done flow calculations and have said an ej25 will only flow enough exhaust out to for a 2" exhaust.

You're having exhaust leaks it either from worn mounts, bad mating flanges or a combination of both.

[evolegacy]

seems like, from what you all have told me, that my current setup is more for a turbo/highly modded engine, neither of which I have. I figured that the blown gasket was from the broken bolt on the driver side mount from the previous install (overtightened) was causing the gasket to go on me, I just wanted to verify that because it was fine for a few months.

So final verdict, according to what you guys have told me, I should downgrade to 2" or 2.25" piping and go with a cat that is a little more restrictive.....does stromung sound like a good idea? if so, should I keep the headers that I have or go with something like OBX EL headers?

[99SUS SFD]

You'll lose the "boxer rumble" with EL headers.

[1996Battlewagon]

Yep, your headers are fine for what you want; just keep them. Your plumbing on the other hand is probably too big. You're actually probably losing backpressure with a 2.5", which means less torque down low. You don't have a turbo and you don't have a H6 and you don't have cams; so you don't really need what you have. I'd go to 2.25" piping and hold on to the rest of it for when you get cams.

[Reason]

Ues all OEM subaru gaskets. For the manifold use OEM gaskets and red RTV, the rest of the gaskets you don't need to. Keep your piping at 2.25", no more. If you want to change anything, change that muffler out with an N1 style muffler. Stromung is nice and sounds awesome but it's a lot of money.

[sexystover]

fix the broken bolt first, either drill and tap or get new heads

[evolegacy]

Ues all OEM subaru gaskets. For the manifold use OEM gaskets and red RTV, the rest of the gaskets you don't need to. Keep your piping at 2.25", no more. If you want to change anything, change that muffler out with an N1 style muffler. Stromung is nice and sounds awesome but it's a lot of money.


money isnt that big of an issue for me since I live at home and only have a few small bills to pay, and I can't keep my piping at 2.25" if its not already there! lol! so the situation atm is fubar until i get the money to change out the system, which shouldnt take long, 3 weeks at most unless i decide to work O.T.


fix the broken bolt first, either drill and tap or get new heads

I'm going to drill and tap it, if its a sucess, yay!, if not, then I'll have to pick up another set, but the break isnt bad, imo anyways, I'll snap a shot of it either tonight or 2morrow and show you it.

[sexystover]

im in the same position, i snapped 2 studs off, one on each head, so i drilled one, but it wasnt a perfect drill so i had to go up a size and then it went through the head to the coolant passage and the other one is so close to the frame rail i cant fit the drill there to drill it so i think im just going to get new heads since i want to build my block anyway, so good luck with yours

[ScaryFatKidGT]

WOW so seriously instead of getting a $600 stromung exhaust to go down to 2.25" I'd spend the money on CAMS! then you could brag that you have the 2.5" piping for a reasin lol, instead of just getting a different exhaust id get some stage 2 regrinds...if you wana go that way but then you wont have a worthless exhaust laying around and you will have more power

[ScaryFatKidGT]

but I also have a question and ill try to keep it in here instead of making new threads about the same thing

I'm all set to buy a almost brand new OEM STi cat-back which is 60mm (about 2.55") I was under the impresson the whole 2.25"-2.5" debate was personal preferance as long as you didnt go to 3" you were good, but you guys seem pretty set that 2.25" is best I am planning on getting some borla knockoff headers, fab up a hi-flow cat pipe and then down the road get cams and/or a wrx turbo kit (but then I wouldn't need the borlas) so would 2.5" be hard on the car at all? and would I actually LOOSE tq or would I just not gain as much as I would with 2.25" piping till I install the cams?

I guess I could always go with the OBX 2.25" cat-back off ebay Because that was the other exhaust I was looking at but its almost double the price

And I though there was a dyno graph somewhere that someone talked about in a similar thread that showed there wasn't much difference between a 2.25" and 2.5" with just some bolt-ons on it?

[rougeben83]

but I also have a question and ill try to keep it in here instead of making new threads about the same thing

I'm all set to buy a almost brand new OEM STi cat-back which is 60mm (about 2.55") I was under the impresson the whole 2.25"-2.5" debate was personal preferance as long as you didnt go to 3" you were good, but you guys seem pretty set that 2.25" is best I am planning on getting some borla knockoff headers, fab up a hi-flow cat pipe and then down the road get cams and/or a wrx turbo kit (but then I wouldn't need the borlas) so would 2.5" be hard on the car at all? and would I actually LOOSE tq or would I just not gain as much as I would with 2.25" piping till I install the cams?

I guess I could always go with the OBX 2.25" cat-back off ebay Because that was the other exhaust I was looking at but its almost double the price

And I though there was a dyno graph somewhere that someone talked about in a similar thread that showed there wasn't much difference between a 2.25" and 2.5" with just some bolt-ons on it?

2.5" and 2.25" either one is fine. I had a 2.5" mandrel to an sti catback and an EL header when I was on the original engine. I had no perceivable loss of "torque" even when I had it bolted up to the stock manifold, then to a borla knockoff, and then finally to the TWE header. STi catbacks are 60mm, a little over 2 3/8". It's a good sounding exhaust. My only reason to definitely go with a 2.5" is dependent on your future modifications (namely, headwork and cams; the real power adders for these engines). It pays dividends to only buy your exhaust once. Otherwise 2.25" is better because it's cheaper.

Stromung is too much money for what youre getting, but that's just me. I'm sure their materials and workmanship are quality, but the tone is too raspy for a lot of folks and a $200 exhaust shop job will do exactly what their exhaust will do.

And backpressure is bullshit when it comes to exhaust design. Don't let anyone tell you otherwise. Its all about exhaust velocity. Gas velocity is directly related to gas temperature. The hotter a gas is, the faster the molecules are moving. Too big of a pipe and the gas spends too much time in the system and it cools and slows down. This is where you notice the loss of power from going with too big of an exhaust. Too narrow of a pipe and youre creating turbulent flow. The best of both worlds in an exhaust getting just enough diameter that will create smooth laminar flow while keeping the exhaust temp high, helping it get out of the exhaust faster (this is helpful for things like scavenging). Google more because I just gave a sort of layman explanation about this...

[ScaryFatKidGT]

Sorry you are correct 60mm is a little under 2.5" I was looking at a jacked up ruler

Thx it's nice to hear from someone who has done this and had it on stock and borla headers. I'm guna go with it, and I'm planning on getting cams and at least an exhaust port match when I get headers might do head work when I do cams but idk yet

[evolegacy]

hmm, maybe i should just go with getting the cams done as well, I was thinking pistons too but that wont be for a while.

question on the port matching and port polish, anyone know where i can get it done in the north shore area of MA and when should i do it?

[rougeben83]

Sorry you are correct 60mm is a little under 2.5" I was looking at a jacked up ruler

Thx it's nice to hear from someone who has done this and had it on stock and borla headers. I'm guna go with it, and I'm planning on getting cams and at least an exhaust port match when I get headers might do head work when I do cams but idk yet

You can weld it up to either size pipe TBH. If you want just a 2.25" muffler, get an 04+ WRX muffler (ie non STi stamped tip), those are actually 55mm and have an extra baffle or two to quiet down the exhaust - this is especially important to an NA engine because there's no turbo there to act as sort of another muffler (my swap is actually quieter than my old na engine with bolt-ons, and its basically a straight pipe to the muffler)


hmm, maybe i should just go with getting the cams done as well, I was thinking pistons too but that wont be for a while.

question on the port matching and port polish, anyone know where i can get it done in the north shore area of MA and when should i do it?

You don't really need pistons, but if you want to work the block, I suppose you can for higher compression (I know some guys on NASIOC have gotten some of their ej25 blocks to around 10.8-11.ish). You can try to get extra displacement out of it, but there really isn't much in terms of boring out the block (not enough material) or changing the stroke...IIRC someone tried to do this and got under 100cc of extra displacement. Again I'm going completely on memory of stuff I just read casually at least 1 year ago so I'm not 100% definite, all I can do is say that this has been done before and point you in the right direction.

And save the $$ from getting a HFC unless youve done all of the engine work already... someone on NASIOC (williaty) just dynoed his engine with both stock cats and a track pipe back to back, the dyno graphs showed basically no change.

Headwork and cams go hand in hand, if youre getting the aggressive cams, headwork (valve job, pnp the ports) along with pnp intake manifold, pnp tb will really make the motor breathe and make use of the larger exhaust system.

[evolegacy]

well, I've been following up on Perdue's N/A guide post from a while ago and follow what others have said, so I do plan to do a lot of work to the engine itself to gain more power from it while trying to keep it street legal.

ok, back to main topic, if I keep my current exhaust system, the borla headers, magnaflow cat and muffler on the 2.5" plumbing, would going with more aggressive cams such as the stage I cams from TWE even things out or do i need to do more?

[ScaryFatKidGT]

I think ur exhaust is fine I wouldn't worry to much about the pressure its not like you have a 3" exhaust so you should be fine

Cams would be perfect for a 2.5" exhaust but your not going to get much more power from stage 1's maybe like 20hp from cams alone, I would go with stage 2 cams unless you were set on keeping the stock ecu for along time then a really aggresive stage 1 would be my choice with stage 1 or 2 PnP. Stage 2 cams will work fine with the stock ecu if you keep the stock redline but if you got stage 2 cams, stiffer springs, port match the manifolds and a stage 2 PnP on the valves, heads and TB you might want a different ECU.

and you dont have to get cams I just think it would be silly to spend money on a new SMALLER diameter exhaust when ur plan is to build the engine up later

[Huffer]

^^ you really should stop throwing random HP numbers out.

[evolegacy]

aright, in any case I've decided what i am going to do, thanks to your help guys.

I'm going to pick up an N1 Muffler and weld that on in place of my current Magnaflow super 44 muffler. I'm having the custom exhaust makers re-build my plumbing for a smaller, 60mm setup. And if I can get the stud out of the manifold, the headers stay. if the headers go on me I'll have to find heads to replace.

I'll post a before and after sound clip of the exhaust when i get this done, most likely I'll be ordering the muffler next week and should have this bolt issue taken care of before then.

[evolegacy]

::bump::

emailed the exhaust tech tonight, hope I hear from him soon.

WCS, does anyone know where to snag an AXLE-BACK N1 Muffler? can only seem to find full systems, although the prices aren't so bad.