Custom Exhaust System

[GrassyKnoll]

Ok, so im tired of the lack of Legacy Exhaust kits so I'm building my own.

I was wondering what people's thoughts are on stock diameter exhaust vs. improving. I would like to improve performance obviously but I heard too big of a diameter is bad. If stock diameter is the way to go, then would it be ok to keep the existing pipe?

I was planning on getting a Random Technology High-Flow Cat along with a muffler / exhaust tip and keeping the existing piping. Would this work okay or would it be much more adventageous to replace piping (with same diameter or bigger?) Thanks

[NewGenSTi]

I would say 2 inch or 2 1/4 would be sufficient.. most turbo vehicles come with 2 1/4 or 2 1/2 and upgrade to 2 1/2 or 3
I believe stock a tad smaller than 2. so your best bet might be a 2 inch exhast system

[badbasser98]

Why not just change the piping? Pipe is cheap, you will be spending all your money on the cat, muffler, and other goodies. If you are going to do it, do it right.

I believe that NA stock Legacy's are between 1 7/8" to 2" in diameter. I wouldn't recomend going above 2 1/4" on a non-turbo engine...

[strat81]

your exhaust will only flow as well as it's smallest point.

upgrade to 2.25" piping. it'll give you a nice top end gain without sacrificing low end power.

[Sarra]

your exhaust will only flow as well as it's smallest point.

upgrade to 2.25" piping. it'll give you a nice top end gain without sacrificing low end power.

that's mostly correct. However, on a 2.2, you may lose a bit low end grunt.

For best results, open up the intake as well as the exhaust. The right intake, header, cat, and cat-back will result in an increase everywhere in the rev-band, not just the top end. :)

go for it. 2.25" is good, 2.5" if you want to upgrade the cams, or super/turbocharge it.

[strat81]

i never said you might not lose a bit of low end... but you don't completely sacrifice low end with 2.25" because you still maintain enough exhaust flow velocity to make power down low :wink:

[GrassyKnoll]

Right. Thing is> Stock is 2.25 (I have 2.5L on the GT)

I already have custom high-flow intake and BORLA headers

I'm getting the Random Technology high-flow cat (bolt-on/stock size)

So the question is, what to do cat-back?

[Plays_with_Toys]

I've not heard that the GT has 2.25"... I'd double check, because I know alot of people who have upgraded their exhausts to 2.25" on the GT/outbacks, and if the piping truly was 2.25 mandrel bent from the factory, people wouldn't be swapping out, and I think L owners would be looking for those pipes so that they could upgrade.

[legacy92ej22t]

Go with a mandrel 2.25" if you are pretty much staying stock. go mandrel 2.5" if you're going to do other engine mods. Also replace the headers. You only flow as well as your smallest point.

[Reason]

Are you talking about the mid pipe? If so get a Stromung mid pipe. It sounds good with my SPT axle back. It will sound great with a Borla header and high flow cat.

[badbasser98]

I highly doubt your car has stock 2.25" exhaust piping. If so, your must have been the only one. Mine doesn't even have 2.25" piping. But it will this summer :twisted:

I would seriously double check the diameter of the piping on the car. Even if it is stock at 2.25" as you claim... I would not exceed this diameter, unless as Sarra said, you turbo or supercharge it.

+1 for the Stromung mid pipe.. I would recomend the Stromung high flow cat pipe too :wink:

-BB98

[strat81]

mandrel bends will not make a noticeable difference on an NA car... press bent will suffice. avoid crush bent if you have a system bent for your car.

as for the stock piping being 2.25", i also highly doubt it..

cat back... go with your choice of muffler, your choice of tip, and have a local shop bend up a 2.25" system for you. (make sure they do press bending and NOT crush bending) best muffler choices will be a straight through design (borla, dynomax, magnaflow, etc). i'm partial to borla myself.

[mr_choung]

stock GT is NOT 2.25..more like 2!
the cheapest route to go is like mine, wrx mid-pipe, wrx axle back.
PLUS it STAINLESS STEEL!

[GrassyKnoll]

aight thanks guys.

I just ordered the Random Technology high-flow cat.

Now im trying to decide between the Stromung mid-pipe + some sort of muffler rig or going with a cat-back system.

Any of you guys have a cat-back system in mind for around $450 or less? Does the Stromung cat-back sound nice? I would kind of like a loudish sound.

[Sambo]

Ok so is the ej25 supposed to have 2,2.25 all the way back? Mine has a 1 7/8 (if not smaller) and its all stock. Im trying to make a custom exhaust setup. from reading this i think im going to go 2... maybe 2.25. heres a crazy question... how bad does putting 2 inch piping on affect the gas mileage?

[ouch1011]

Stock for both 2.2 and 2.5 is about 1 7/8". I compared the stock exhaust from my BD GT vs a GC L I had as a parts car. Aside from the exh system length, the they were exactly the same, including diameter.

The stock exhaust on my BL GT is only a smidge over 2.25" (its actually 60mm, or about 2.38") and its got about 100hp on the BD. So yeah, no way stock BD exhaust is 2.25"

I went with 2.25" on mine mainly because it was easier to find exhaust parts in that size and because I have headers. If I was keeping the stock manifolds, I wouldn't have gone past 2", because it wouldn't have been worth it. The stock manifolds/cats still neck down to less than 2" in places.

[ScaryFatKidGT]

Are you talking about the mid pipe? If so get a Stromung mid pipe. It sounds good with my SPT axle back. It will sound great with a Borla header and high flow cat.Where? I called boxer4 and they said they were discontinued and I could only get them in a 10+ group buy.

[TGX4776]

Get a Vibrant Street power muffler. Makes it deeper and looks stock.

[90lsturbo]

so if i went 2.25 on my 00 bh i shouldnt ahev that much exhaust flow loss at the mani folds being less right

[Wiscon_Mark]

Where? I called boxer4 and they said they were discontinued and I could only get them in a 10+ group buy.

Check the dates, Shane made that post 5 years ago.



so if i went 2.25 on my 00 bh i shouldnt ahev that much exhaust flow loss at the mani folds being less right

If you're going 2.25" do it all the way from the engine to the muffler tip. It won't really benefit you otherwise. Remember that exhaust gasses spreading out, cooling down (and as a result slowing down) causes backpressure which hurts torque and horsepower.

[SativaMan04]

Do headers cause a CEL light? Will throwing in a high flow cat decrease gas mileage? Will I still be able to pass smog in CA with headers and a high flow cat?

[Huffer]

^^ how long is a piece of string?

Some headers cause a CEL- though normally people that it happens to have a high flow cat or a track pipe.
You can just buy headers and a high flow cat, install the headers, go get smogged, then get home and swap the cat section for the high flow unit.

[SativaMan04]

I actually want to have a setup like your's Huffer. Headers, keep stock cats, and STI muffler. Did that mean you had an exhaust shop customize your midpipe? So, Im assuming they welded your stock cats and resonater to the custom piping?

Thanks Huffer.

[Huffer]

^^ no - I installed my Borlas when my timing belt was being done, and had previously had a shop fab up a custom midpipe with my old stock flanges, and then they mated that to my STi axleback.

Borlas - stock cats - custom midpipe - STi axleback (w/ modified hangers)
Total cost of the exhaust has been around $300 installed, including parts n labor. This is over 2 years. I'm kinda patient.

[SativaMan04]

Sweet I can't wait to hear the sound clip!