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Old 09-29-2004, 10:24 PM   #1
jamesfacts
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Impreza GC8 Should I do this to a stock EJ25 header?

I have the opportunity to pick up an extra header for my car... so I've been thinking I'll just make some minor modifications to it.

I'd like to port it, strip the heatshields off and gutt the cat.

Is this a good plan? What might I break/damage?

Thanks,
James
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Old 09-29-2004, 11:08 PM   #2
Patrick Olsen
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There's little chance you'll break anything, and there's little chance you'll gain anything. The stock header/cat arrangement is so retardedly convoluted that no amount of porting is going to make any difference. A gutted cat may help a wee bit, but you'd be better of just getting rid of it.

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Old 09-29-2004, 11:12 PM   #3
jamesfacts
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I suppose, but I want to keep this on the cheap. I'll only spend money for the wrap I'll need to replace the heatshields, and I'll have a spare for emissions time.

Thanks,
James
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Old 09-30-2004, 01:17 PM   #4
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Bump... any more insight?
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Old 09-30-2004, 02:50 PM   #5
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Sounds like it might be more work than its worth

(go huskies? you go to UW?)
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Old 09-30-2004, 03:05 PM   #6
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please don't gut the cat... there really isn't that much to be gained from it and you'll pollute a lot more.
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Old 09-30-2004, 03:30 PM   #7
jamesfacts
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Well, I have three cats, so I figuire loosing the pre-cat won't make that big a difference, will it? This is all on a spare set, so I'll go back if I don't like it.

As for the Huskies... I go to UCONN.
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Old 09-30-2004, 03:39 PM   #8
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3 cats? Do you own a WRX or an RS. The RS's only had 2 cats and they are not redundant. The both have different chemicals in them to clean different chemicals from the air. When you buy a replacement cat it will often be listed as a 2way or 3way. This means it has both chemicals in one cat.

As for your other intended mods, removing the heatshields and them wrapping the header will do very little for you.

Porting the flange where the header meets the head might help a minute ammount if done correctly, but there is no way you can get far enough into the header to make it flow any better.

Just save your money and buy a real header.

J
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Old 09-30-2004, 03:46 PM   #9
HeMan1320
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get it extrude honed...(SP?) but that's money you prolly don't wanna spend.
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Old 09-30-2004, 10:50 PM   #10
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Extrude honed? It tubular steel already.....stamped halves forming a tube for the first pairings. There's not much material to take off. The many responses to look at other headers for any kind of gain didn't get posted by accident.

If you buy a spare manifold....look at it closely and then try to figure out how you can make it better without totally getting rid of the crappy collector.

Jay Storm
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Old 09-30-2004, 10:57 PM   #11
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my '04 RS definately had 3 cats. Anyway, I think I agree with everybody that there is not much point. Save and wait for a used Borla header or something. They aren't great, but it'll help a bit at least.
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Old 09-30-2004, 11:32 PM   #12
squeech
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GC RS = 2 cats in midpipe
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Old 10-01-2004, 03:25 AM   #13
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My 03 has 3 cats.

The stock heat sheild would be better then heat wrap.
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Old 10-01-2004, 09:10 AM   #14
Pat L.I.
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If the 03's and 04s are like MY02. What you are thinking is the third cat is actually a pre-res chamber on the midpipe.

Gutting any cats will make your car sound horrible, and you will notice little to no gains, pollution of the air increases, and you will have to deal with the smell which will give your girlfriend headaches!
If you are looking for a cheap solution look at the borla headers. They give a great sound, and a small boost in power. Certainly more than you will see from toying with the stock headers. At 220 they are not THAT expensive.

Do you have anything else in the intake/exhaust system modified?
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Old 10-01-2004, 12:44 PM   #15
jamesfacts
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Quote:
Originally Posted by jeffg
3 cats? Do you own a WRX or an RS. The RS's only had 2 cats and they are not redundant. The both have different chemicals in them to clean different chemicals from the air. When you buy a replacement cat it will often be listed as a 2way or 3way. This means it has both chemicals in one cat.

As for your other intended mods, removing the heatshields and them wrapping the header will do very little for you.

Porting the flange where the header meets the head might help a minute ammount if done correctly, but there is no way you can get far enough into the header to make it flow any better.

Just save your money and buy a real header.

J
Save my money? I'm getting this free!

I thought I had 3 cats... is it just a resonantor in the midpipe, perhaps?
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Old 10-01-2004, 12:47 PM   #16
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Quote:
Originally Posted by Pat L.I.
If the 03's and 04s are like MY02. What you are thinking is the third cat is actually a pre-res chamber on the midpipe.

Gutting any cats will make your car sound horrible, and you will notice little to no gains, pollution of the air increases, and you will have to deal with the smell which will give your girlfriend headaches!
If you are looking for a cheap solution look at the borla headers. They give a great sound, and a small boost in power. Certainly more than you will see from toying with the stock headers. At 220 they are not THAT expensive.

Do you have anything else in the intake/exhaust system modified?
Ahh... I see.

I know what the impact would be if I gutted all the cats... just curious what would happen if I gutted one, as I didn't think aftermarket headers even had cats (typically, I know you can buy them w/ cats)

As to the Borlas, I'm not going to bother w/ those. They are not going to give me any gains at all... and lord knows how long they'll last.

The other I/E mods I have are: 3" intake w/ K&N panel filter, WRX axleback.
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Old 10-01-2004, 12:52 PM   #17
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You dont think borla headers will give you anything, and you think messing up the stock headers will....

And actually no headers have cats in them. The cats are bolted to the headers.

How about this.... you go do whatever you want to your car, you obivously have it set in your mind that its the greatest mod ever, regardless of what others might know.

Have fun
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Old 10-01-2004, 01:05 PM   #18
jamesfacts
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Quote:
Originally Posted by jeffg
You dont think borla headers will give you anything, and you think messing up the stock headers will....

And actually no headers have cats in them. The cats are bolted to the headers.

How about this.... you go do whatever you want to your car, you obivously have it set in your mind that its the greatest mod ever, regardless of what others might know.

Have fun
I don't have anything set in my mind man, I just thought it might be interesting to see what it would be like if I messed around w/ a spare header.

I didn't say I knew what would happen... that's why I posted this.

If you'd like to offer advice, fine...
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Old 10-01-2004, 03:14 PM   #19
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Honkey3k has a Borla SS header and highflow cat ( which also eliminates one cat )on his 98 Legacy OB. It has a 2.5 and with the new additions, it revs alot quicker and pulls waaaaay harder. I suppose you could go to an exhaust shop with your whole cat pipe ( that has both cats ) and have them make you a custom pipe that uses one of your stock cats ( so you can have some resistance ) and eliminates the other. Then find a cheap header and your good to go. I bet you could have that custom cat section made for under $50. The guy will probably tell you he cant make the pipe because it would be illegal to put on your car. Just tell him its for an offroad vehicle.
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Old 10-01-2004, 04:39 PM   #20
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americanyouth,
I don't think that you will get very much from doing anything to the stock headers. From my understanding, is that they have a lot of turbulance inside them throughout, I am not certain on this though. You are probably better buying some aftermarket headers. However, that being said, it would give you a chance to practice portin n polishing on the flanges if you want, or something else. Practice never hurts I suppose. You should work on finishing the catback and a high flow cat, just a thought. Any way good luck
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Old 10-01-2004, 04:53 PM   #21
jamesfacts
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Quote:
Originally Posted by CatchMyDrift
I bet you could have that custom cat section made for under $50.
I'll have one eventually... right now I'm trying to avoid spending money.

impy.... I'll report back w/ my results.
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Old 10-01-2004, 08:43 PM   #22
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Quote:
Originally Posted by americanyouth
As to the Borlas, I'm not going to bother w/ those....... and lord knows how long they'll last.
They have a great warenty I belive.
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Old 10-01-2004, 09:44 PM   #23
jamesfacts
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Quote:
Originally Posted by RS_to_WRX_swap
They have a great warenty I belive.
I don't buy things new.
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Old 10-01-2004, 10:09 PM   #24
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I'm currently modifying a set of headers for my OBS-S (Supercharged Outback Sport)
Straight back into a X pipe than out the sides, just in front of the rear wheels
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