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Old 30th September 2011, 02:52   #1
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Getting most HP out of stock exhaust

Correct me if im wrong but wouldnt the majority of the 40-50hp gains seen from doing a full cat back exhaust be mainly from the removal of the secondary cats? Has anyone just gutted their stock cats or is there piping sold that bolts on to replace that section? If you dont care that much about sound do you really need to upgrade the whole system or wouldnt the majority of the HP gains come from removing those secondary cats?
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Old 30th September 2011, 03:42   #2
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I think you mean primary cats, and it has been done. Some people have hacked them off and put in straight pipes.
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Old 30th September 2011, 04:49   #3
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I could be wrong but from my understanding the primary cats are connected to the stock headers so you cant just cut them out and replace them with straight pipe. If you are doing a cat back exhaust system most of the power gains come from section 1&2 which is where the secondary cats are as well as the stock x-pipe and resonator is. All that stuff restricts flow which is why you can get some good gains by changing those sections. The big HP/Torque gains come from changing out the headers and going to a high flow cat. Hope that helps.
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Old 30th September 2011, 06:41   #4
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Dont really want to go the headers route esp b/c im still under warranty. Seems like the most expensive part of these exhausts for sale are the mufflers. thats why many of these i see like eisemann and tubi,etc.. are the same price if not more for just the mufflers opposed to say the full system which RPI and agency power offers. Has anyone done piping that will just remove the secondary cats and resonater? If so who sells the piping? I cant hack apart and weld my stock exhaust b/c if a problem arises i need to put it back on for warranty. Any idea's?
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Old 30th September 2011, 07:14   #5
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Any good muffler shop will be able to do a resonator delete or remove the secondary cats. But if you are really concerned about your warranty doing that would be the same if not worst then just replacing the full system. I personally have the Magnaflow section 3 and did a resonator delete and it sounds really good. Not nearly as loud as Tubi for example. In terms of HP gains I doubt I picked up anything. If you truly want more power just spend $3000 and get the RPI or AA full cat back system and youll be happy.
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Old 30th September 2011, 09:29   #6
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Actually, what I was saying was that the majority of the power realized from exhaust mods are found from removing the restrictive primary cats attached to the headers. RPi tested the stock headers and found the design to be solid, hence their focus on just the primary cats. I can attest that a full RPi exhaust is a definite jump in power, but the primary cats are the key to a big horsepower gain.
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Old 30th September 2011, 16:12   #7
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I am stuck on thesameissue as well,as I have been contemplating removing the primary cats. Due to the complexity involved in removing the primary cats which could possibly result in damaging the headers wall,I was inclining going down the same route as rpi or evolve exhaust.But if it is just removing the primaries then I couldnt justify to myself spending $3000 on copied design without cats. I would rather take the risk with drilling them out as they cant cut and welded with straight pipes.

My question is : if I cut the secondarycats out what power gains will I be getting,as they are so easy to weld back on.

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Old 1st October 2011, 01:46   #8
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I saw post were a member did this mod ( sencondary cat del.) and picked up 12-13 hp on a dyno.
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