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CAUTION!!!!
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9,883 Posts
its not restrictive at stock power levels, but once you add heads, cam, LTs and so on, then yes, the 04 2 inch piping does inhibit a bit of power.
 

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Premium Member
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1,281 Posts
Not just more HP.

GMLIFER said:
is it that restrictive, am i going to see enough hp gain to justify $700 or more?
Hi GMLIFER. Justification depends on you. I have an 04-A4 and I recently installed a Magnaflow catback on mine. What a difference in breathability. As well as noticing an increase in hp,I actually get a few more miles per gallon.
Oh, and the sweet sound and no cabin drone.
And as far as the stock system being restrictive, Just get under there and look for yourself.They are also lighter than stock and are an easy install.
Now, before you get if you do get, Their are several to choose from ie; Magnaflow(stainless)-Flowmaster(aluminized)-Corsa(stainless)-Borla Not sure of etc. You may want to listen to some sound clips to find one to your liking.

I can also share a discount code that this forum has if you don't already know it for Hottexhaust.com and put LS12GTO in the coupon field that brought mine down to $526.90 Shipped.
If you go Magnaflow, The catback for 04's is 15868. If you go with any catbacks, you might want to order the gaskets to replace the originals-or re-use.
 

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Registered
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694 Posts
Discussion Starter #5
i guess my main thoughts are, will some less restructive mufflers be enough or do i needa cat back. Im leaning towards needing it but im just not sure.
 

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Ima lead farmer, motherf__er!
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939 Posts
It would be cheaper to pick the mufflers you want and have a shop bend you some pipe. I went this way instead of spending $700+ on an SLP system because I wanted a dual exit on my 04. Including the cost of the SLP mufflers, it cost me a little over $300 for my cat-back.
 

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F-body owner
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1,437 Posts
If I were in your position, I'd keep the 04 stock catback, and just add some cutouts and save yourself $500+.
 

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Ka-Boom!
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1,987 Posts
Just my opinion but I think catback is more about sound than performance until a significant amount of mods.
 

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Growing up is an option
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17,296 Posts
Hot Sauce said:
It would be cheaper to pick the mufflers you want and have a shop bend you some pipe. I went this way instead of spending $700+ on an SLP system because I wanted a dual exit on my 04. Including the cost of the SLP mufflers, it cost me a little over $300 for my cat-back.
there's is no compelling reason to get a cat back. if you start making more HP just do the mufflers and get some 2 1/2" pipes bent from there to the tips. those pipes stock are 2 1/4" with some pretty good crimps. you're already 2 1/2" from the manifold to the muffs now.
 

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Go Tigers!
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2,455 Posts
svede1212 said:
there's is no compelling reason to get a cat back. if you start making more HP just do the mufflers and get some 2 1/2" pipes bent from ther to the tips. you're already 2 1/2" from the manifold to the muffs now.
Not this is some good advice. :hail:
 

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Objects in mirror dont matter
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3,777 Posts
Do you have the cam in your sig actually in the car? Big cam, with big exhaust wants big flow. I love the sound of my o4 catless with LTs on the stock back half. Perfect tone, absolutely collecting compliments at full throttle all the time, but no drone, stc.
I would love to see the dyno #s after tuning that cam on a stock catback, as I am hoping my 3" cutouts give me a big hit and it would be snice to see what you made with the stock catback. I decided not to give up on the sound, and use variable opening electric cutouts for that extra power moment now and then.
My tuner and head builder think my factory catback is holding me back from at least 25 hp with my combo in sig. We shall soon see.

PS EDIT...I just looked at your dyno thread. You would pick up a little with a pair of cutouts, and keep the sound you love.
I swapped heads too, and got like 396 through 3.91 gears, which show about 10% less on the dyno. I have my cutouts in a box, waiting to go on in a week or so.
 

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hello officer...
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447 Posts
climb under ur car and take a look, theres tons of kinks that were put there for sound that restrics airflow. IMO it was worth it.
 

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Objects in mirror dont matter
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3,777 Posts
bryced1 said:
climb under ur car and take a look, theres tons of kinks that were put there for sound that restrics airflow. IMO it was worth it.
No doubt, the stock 04 catback sounded tons better than the quickly cobbled together 05 setup, but correct, it was more than adequate for bolt on or stock, but when flowing big cam at 6800rpm, those sound and clearance kinks are a bit much. I just don't want to sound any louder. 240 exhaust duration and big valves= every cop in my zip code knows when I am coming now, and it would only get worse with true 3" and Magnaflows, which were my choice before I decided to go cutout. On highway, you can partially open them for flow, and race time, open em all the way for no restriction, as both mufflers and open cuts are dumping exhaust.
If I hate that, I will go local shop fabbed with Magnaflows. Save lotsa money.
 

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Beer Geek
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3,713 Posts
+1 on svede and swampgoat's comments. The stock system is fine on a stock drivetrain, but just barely.

With a big cam, even allowing for a conservative tune, the stock system is already holding you back.

You don't have to blow $700 on a bolt in cat back though. I have no idea how shop rates in TX compare to rural NC, but I got quotes from two different custom shops for a full custom system built on quad two inch pipe, both shops came in under $500 using SS tubing.

All you really have to do is pick what kind of muffler sound you like (chambered, absorbtive, etc) and find a shop. You are size limited on the 2004 same as me, but if you drop the underskirting behind the rear axle you'll have about 35" horizontal to work with on each side and plenty of room for 5x9 ovals.

Probably want to fab up some kind of heat shield for the passenger side. So you'll need a piece of donor sheetmetal, old washing machine or whatever; a few minutes with a hammer and some spray paint. This isn't rocket science. Might as well invoke a good Sears stick welder and some angle iron while you are gathering materials.
 
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