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Old 12-16-2009, 04:04 PM   #1
Aaron1121
 
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High Flow Cats with Shorty Headers?

I am installing a catback system. I would love to also install some long tube headers, but since I live in the golden state I won't pass a smog inspection with them. I don't really feel like swapping out the headers before every smog inspection.

From everything I've seen on the forums, it looks like most people are seeing 25-30 HP gains with longtubes and high flow cats, and people with shorties and stock cats are getting 4-9HP. It seems like the most restrictive part is the stock cats.

Has anyone tried just replacing the stock cats, or shorty headers with high flow cats? What type of gains have you seen?

If shorties and high flow cats worked well, it would be pretty easy to just swap the cats with a couple bolts prior to the inspection.

Thoughts?
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Old 07-02-2010, 03:46 AM   #2
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Old 07-02-2010, 03:55 AM   #3
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Different cars but a buddy of mine with a G8 has shorty headers with stock cats and a corsa catback and made 20 less rwhp than myself with solo high flow cats, stock manifolds and solo catback. We have got our tunes from the same dyno also. Personally I think you may gain a little power in the mid range but not enough to warrant the cost of shorties unless you want more sound to go with your high flow cats. Well if you plan on going the maggie route you may have to get shorties anyway to get as much flow as possible.
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Old 07-02-2010, 05:54 AM   #4
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first u dont have to smog ur car for atleast 5 years since its new. 2nd tons of smog shops out there look to see if u have cats, thats it. not if theyre relocated not if u have LT's. if you have cats then ur good. u just need to find one. and u can install LT's and Catted mid pipes.
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Old 07-02-2010, 06:53 AM   #5
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check my thread out aaron, you may find it helpful. I have DT shorty headers and SOLO hiflow cats.

http://www.camaro5.com/forums/showthread.php?t=91945
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Old 07-02-2010, 10:15 AM   #6
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Regardless of what "some shops" may do/say, the letter of the law states that if you move or replace FUNCTIONAL cats, you are in violation of the inspection. Take it for what's worth and make your own decision from there.
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Old 07-02-2010, 10:25 AM   #7
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Quote:
Originally Posted by axis View Post
Regardless of what "some shops" may do/say, the letter of the law states that if you move or replace FUNCTIONAL cats, you are in violation of the inspection. Take it for what's worth and make your own decision from there.
I am hoping the Magnaflow replacement cats I am getting will fool the visual inspection, since they look identical and flow a bit better, or so they say. I won't know until I get them installed (parts are ordered, install not scheduled, yet) and go through inspection (September).
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Old 07-03-2010, 07:54 AM   #8
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Gen III/IV engines essentially have shorty headers from the factory. In other words it's a gigantic waste to buy an aftermarket set. I am just starting to really learn about the 5th gen so I don't know what all is available at this point, but if there is a 50 state legal (C.A.R.B. approved) mid length header available that may be something you want to check into. Those will not move the cats back like LTs do and would be 100% legal. Also, as true as it is that swapping working cats is illegal, good luck to any inspector that tries to prove they didn't replace dysfunctional cats or ones that were removed by another owner. If you have cats and EGR you can often pass a visual with LTs too but with that one you're really at the mercy of the inspector. If they look for the C.A.R.B. sticker on the headers you will have a problem. Granted nothing stops you from going to as many shops as you need to in order to pass. If you don't mind some possible hassle I'd get LTs with emissions hookups and some high flow cats.
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Old 07-03-2010, 08:43 AM   #9
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Not a gigantic waste since. The DT Shorties are lighter weight, look better and because of the ceramic coating, will allow less heat into the engine compartment. That is why I am going with them.
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Last edited by bi11ymc; 07-03-2010 at 08:44 AM. Reason: waste (not waist) lol
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Old 07-03-2010, 09:23 AM   #10
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Quote:
Originally Posted by bi11ymc View Post
Not a gigantic waste since. The DT Shorties are lighter weight, look better and because of the ceramic coating, will allow less heat into the engine compartment. That is why I am going with them.
1. Lighter weight by how much? Is this weight savings anything that will ever be discernible to you? I think not unless you are building a drag car and are doing several other things along with it that add up to a large overall weight savings.

2. If a $500 (plus hassle or cost of install) under-hood decoration is your thing that's your business. This is America.

3. Lower temps in the engine bay are a plus, but assuming the current heat is not causing any problems I don't see how this is a major factor? If it was you would see it reflected on dynos. On a stockish car the only purpose I could see it serving is maybe (big maybe) helping hoses last longer. Those should really be changed long before they have a chance to be a problem though.

I will concede that they are at least a little better than stock manifolds and may manifest a more notable gain over stock manifolds on a decently modded engine or a high RPM application than they do stock. I do see that you have a cam coming soon so maybe that will make them a bit more useful. Just speculation there. But what is not speculation is the for the cost/hassle involved I personally find shortys on LSx engines extremely underwhelming. Its not my goal to attack you dude and sorry if my opinion offends you but it is my opinion. I like mods that actually make my car do something notably different than it already does. If you're into paying $100/hp that's your business.
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Old 07-03-2010, 10:43 AM   #11
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Quote:
Originally Posted by Wilburbeest View Post
1. Lighter weight by how much? Is this weight savings anything that will ever be discernible to you? I think not unless you are building a drag car and are doing several other things along with it that add up to a large overall weight savings.

2. If a $500 (plus hassle or cost of install) under-hood decoration is your thing that's your business. This is America.

3. Lower temps in the engine bay are a plus, but assuming the current heat is not causing any problems I don't see how this is a major factor? If it was you would see it reflected on dynos. On a stockish car the only purpose I could see it serving is maybe (big maybe) helping hoses last longer. Those should really be changed long before they have a chance to be a problem though.

I will concede that they are at least a little better than stock manifolds and may manifest a more notable gain over stock manifolds on a decently modded engine or a high RPM application than they do stock. I do see that you have a cam coming soon so maybe that will make them a bit more useful. Just speculation there. But what is not speculation is the for the cost/hassle involved I personally find shortys on LSx engines extremely underwhelming. Its not my goal to attack you dude and sorry if my opinion offends you but it is my opinion. I like mods that actually make my car do something notably different than it already does. If you're into paying $100/hp that's your business.
Why do people change anything about the car? People spend much more just to change the sound with a cat-back and it does nothing to performance. I say, it is only money and if shorty headers allow me to stay in the county I live in, improve many aspects of the car no matter how small, and cost so little, I say "why not"?
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Old 07-05-2010, 06:51 AM   #12
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Quote:
Originally Posted by bi11ymc View Post
Not a gigantic waste since. The DT Shorties are lighter weight, look better and because of the ceramic coating, will allow less heat into the engine compartment. That is why I am going with them.

yes
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Old 07-05-2010, 09:08 PM   #13
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My shorties gave the the car a little bit more growl out of the Solo exhaust and look great for only $200 new.
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Old 07-05-2010, 11:33 PM   #14
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Definitely replace the Cats with some high flow/spun units to realize better HP gains.

Agreed, the factory manifolds are not bad at all.

The Shorties Def give a better look, just don't look for LT Header performance out of them.

Best of luck to you sir!
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