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Old 11-12-2013, 02:16 PM   #99
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well....just since we talked here...I believe there would be something to be gained. But I am adding headers at this point and testing that gain under cam+FI. After that, we'll see if it is still nice on the interstate (no drone) like it is now. If not, then heck with it, it will get 3" all the way out the back. If it stays docile at interstate cruising then I will ride out the 2.5". The car is making power and has ET's to back it up with stock manifolds, no cats, and dual 2.5" custom exhaust, now. LOL
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Old 11-12-2013, 03:59 PM   #100
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well....just since we talked here...I believe there would be something to be gained. But I am adding headers at this point and testing that gain under cam+FI. After that, we'll see if it is still nice on the interstate (no drone) like it is now. If not, then heck with it, it will get 3" all the way out the back. If it stays docile at interstate cruising then I will ride out the 2.5". The car is making power and has ET's to back it up with stock manifolds, no cats, and dual 2.5" custom exhaust, now. LOL
Lol bought time.
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Old 11-12-2013, 07:14 PM   #101
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Lol bought time.
+1. At the very least his car will sound better. Especially if it drones and he goes full 3". It will sound amazing. I know mine does!
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Old 11-12-2013, 10:44 PM   #102
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If I'm wrong about 15 or less hp I'm gonna owe some " y'all told me so's" to u clowns. We'll see soon enough. At least someone will have some printed knowledge when I am done.
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Old 11-13-2013, 06:32 PM   #103
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I know for a fact that a stock LS3 cat back can support 1120rwhp because I just saw it!!
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Old 11-13-2013, 07:35 PM   #104
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Of course it can, but what was left on the table?
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Old 11-13-2013, 08:32 PM   #105
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If I'm wrong about 15 or less hp I'm gonna owe some " y'all told me so's" to u clowns. We'll see soon enough. At least someone will have some printed knowledge when I am done.
Bring it GG! Lol

Take care of our buddy muddflap, I can't wait for his results. What do you think he'll put down?
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Old 11-13-2013, 09:20 PM   #106
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I lost 1/2lb or so from last time. I have the ECS Paxton 1500 kit. The exhaust still necks down to 2.5 at were the cats were.
Bo White, I've been looking to modify my OBX into a true 3 inch all the way. And I thought up a good way to do it cheap. I'm thinking about buying one of those cheap no-name brand cat-backs off Ebay and just using the two pipes that meet the header and go into the mid-pipe. This will eliminate the HF cats or extensions. If you check them out, you can see that these pipes will bolt right onto our OBX headers and then you can connect it to your OBX mids...no necking down to a 2.5 at all. Here is the link: http://www.ebay.com/itm/DUAL-4-MUFFL...00929180796%26

It will cost you $400 including shipping. But it will take like 10 minutes to install. And then you can just sell the rest of the exhaust...or keep it for future use. Not a bad idea eh?! I'm gonna do this!
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Old 11-13-2013, 09:27 PM   #107
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Why don't you just cut the neck off and weld in 3"piping?
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Old 11-13-2013, 09:49 PM   #108
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Why don't you just cut the neck off and weld in 3"piping?
I don't like welds on exhausts. Experience taught me that they leak after some time. And plus, the HF cat itself necks down. So I'd have to cut and weld to that as well. Or I'd have to get 3 inch piping, weld a ball flange to it to connect it to the headers, then cut and weld to the mid-pipes. After all the materials and labor I will probably end up spending the same $400 if not more. And it won't look as good as it will if I use the cheap no-name brand exhaust pieces...
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Old 11-13-2013, 09:54 PM   #109
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An easy cut on some catless connections and a nice clean weld and you're done. Which reminds me.. my shielding gas tank lease is due.
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Old 11-13-2013, 10:07 PM   #110
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the magic number is 2.2cfm /HP. Any more flow is a waste of money.

Here is a decent unbiased article with science behind exhaust system design
Written by David Vizard. That guy knows his sh!t.
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Old 11-13-2013, 10:34 PM   #111
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Why don't you just cut the neck off and weld in 3"piping?
Unless you have mega-rwhp build, that 2.5" neck down connection point between a 3" header collector and a 3" catback can actually help the engine make more TQ. This works because the collectors are then isolated from the rest of the catback system and it "looks like" an open collector to the engines exhaust gas masses and sonic reflections. So why go to the trouble to cut and weld in a 3" replacement section when you very well would cause TQ to fall off?

No offense meant here, and recognizing that this all may sound counter-intuitive, but if willing to forget what you think you know, and consider that what you don't know, is what you don't know...
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Old 11-13-2013, 10:53 PM   #112
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Unless you have mega-rwhp build, that 2.5" neck down connection point between a 3" header collector and a 3" catback can actually help the engine make more TQ. This works because the collectors are then isolated from the rest of the catback system and it "looks like" an open collector to the engines exhaust gas masses and sonic reflections. So why go to the trouble to cut and weld in a 3" replacement section when you very well would cause TQ to fall off?

No offense meant here, and recognizing that this all may sound counter-intuitive, but if willing to forget what you think you know, and consider that what you don't know, is what you don't know...
I know this was addressed towards thahemp, but I feel inclined to comment. I personally can recognize when I don't fully know or understand something. But I also am a creature of passion. Sometimes, I do things solely because I enjoy the thought of it. I understand that I could possibly lose some hp and/or tq by modifying up to a full 3 inch. But for some reason, I just want a full 3 inch system. If I were to definitely lose a significant amount of power, and if that could be undeniably proven, then I would refrain. But the way I see it, there is no significant losses if any losses at all. There are lots of calculations and math to help decide appropriate diameter as we have seen from several members. But sometimes, real world gains vary widely from what you would expect from paper calculations. I feel that a full 3 inch exhaust that eliminates the HF cats will give me a worthwhile boost. And if I'm wrong, then I can always return it to the way it currently sits...no harm done.
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