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Old 03-14-2012, 02:26 PM   #26
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Quote:
Originally Posted by hognutz View Post
Removing Cats never hurts the car. Cats are a restriction in the exhuast for eviromental resons. there is no perfromance or tuning benifit to cats that I have ever heard of.

If it is a track car ditch them. on my 01 mustang GT it had 4 cats and I noticed more power from the midpipe swap than the catback changover. you do get more fuel smell with no cats though. If you will ever drive it on the streets high flows are bit nicer smell wise sitting at a stop light.
One might be lucky to see up to 10 RWHP with a CB, especially on ZL1, because of the valves. If they're anything like the 'Vettes mufflers, internally, it's just a perforated pipe the valves are connected to. If you're running a lot of boost, or moving a lot more air through LSA, then maybe you might see more, but, for the first time, I'm not really considering a CB or a AB I'll still mod' the mufflers, but that will be mostly for sound

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Man they look exactly the same as the ls3 cats... Could be a easy swap to say a solo performance cat and get a nice sound with the valves open.
Getting back to hognutz post - it's my understanding the further you move the restriction from the exhaust port, the less influence it has on efficiency, and ultimately - power (hence why I'm still in a quandry about LTs not necessarily being that effective...). Considering there are four cats' almost immediately downstream of the manifolds, eliminating them, or replacing them with high-flow units would probably be a lot more beneficial than a AB and even moreso, with a CB. I think cleaning-up the headpipe and H-pipe are going to be primary areas for power gain, at mostly modest power levels - probably not a whole lot, but moreso than anything with the mufflers. The pipe size appears relatively generous, though, I don't really like the turns just before the mufflers... Anyways - I'm obsessed with exhaust, so I'm always open to ideas and comments.

I think replacement cats' could be something to consider, especially from Solo

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Also can someone explain the reason why you have a x-pipe or a h-pipe? Why not just have a straight pipe?
Just like adamgl mentions below Having a correct sized H-pipe can enhance scavanging from the exhaust ports by balancing the exhaust pulses as they move down the exhaust. A properly designed manifold (and headers, for that matter) will place the pulses in such a way that while the pulse moves down the exhaust, it moves with little restriction (by way of pipe diameter and shape, among other things) and prevents it from pushing another pulse, closer to it's relative exhaust port, back into the combustion chamber (the most desireable condition, in the combustion chamber, in terms of exhaust, is having a completely clean, new charge, with every new combustion cycle; if, on the exhaust and intake strokes, and residual gas from the previous cycle is left, it will, in essense, contaminate the new air/fuel charge, and lower efficiency and power). Having said that - if we disregard the cats' (for the moment, since we're talking about the H-pipe now), a properly placed (as near the exhaust port as the chassis will allow) and sized H-pipe, will do much the same, as it will enhance scavanging and pull exhaust down the system through vacuum. Some tests show that X-pipes are even more efficient than H-pipes (I believe mostly because the turns are more gradual and ultimately, provide less restriction through smoother-radiused bends).

In the past - tuners and magazines have taken apart OEM H-pipes ('Vetts are what I'm visualizing right now), and what we see on the outside is a lot different than the inside. The inside of the assembly is actually smaller because smaller tubes are implanted, for whatever reason (maybe to keep the heat high ), and I'd read tests where just the mid-pipe was changed with an aftermarket H or X-pipe, with correct sizing, and there were improvements in efficiency and power.

Please don't get me wrong - I'm not poking fun or suggesting GM's exhaust is sub-standard. It looks outstanding from what we can see, and I'm sure testing against aftermarket systems will probably yield little to no efficiency gains. I do know the OEM's have different standards and other considerations to abide by, so sometimes, there are improvements than can be made. I really like the fact there are no resonators on ZL1 and am very pleased with what GM looks like they're giving us. I'll be saving a lot of money over what I thought I was going to have to do to reach my goal in this regard

JMVHO

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Originally Posted by adamgl View Post
It allows scavenging, it pulls the exhaust gases out better than straight pipes.

Gas passed through the x or h from one bank and it helps pull exhaust from the other bank.
I'll be watching ARH and Kooks, among the others, for mid-pipe replacement that include H' or X-pipes It improves the sound a little more, too
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Old 03-14-2012, 02:29 PM   #27
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Here's the one pic' I have of the mufflers from 'Vette, just for referrence.

Sorry - back on topic
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Old 03-14-2012, 09:46 PM   #28
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So radz, from strictly a sound perspective, what would you feel will boast the loudest sound while maintaining the stock mufflers (I like the valve idea) but more importantly, not ruin the efficiency of the exhaust flow?
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Old 03-14-2012, 11:00 PM   #29
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Originally Posted by toilets View Post
So radz, from strictly a sound perspective, what would you feel will boast the loudest sound while maintaining the stock mufflers (I like the valve idea) but more importantly, not ruin the efficiency of the exhaust flow?

what people do is cut the muffler open and take calmps and put them over the perforated section of pipe you see in the picture above. this turns it into as close to stait pipe as you can with the factory system in tact. this is basically like instally cutouts in a way. then you can close the switch to co back to mild exhaust.
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Old 03-15-2012, 10:49 AM   #30
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So radz, from strictly a sound perspective, what would you feel will boast the loudest sound while maintaining the stock mufflers (I like the valve idea) but more importantly, not ruin the efficiency of the exhaust flow?
Like hognutz mentions, below, once you're in the muffler, you could use stainless band clamps, and wrap them around the perforated by-pass pipe. This essentially would seal the perforations, and make the muffler nearly 100% "closed" when the valves were open. Others were doing essentially the same, except they'd cut-out the perforated pipe and replace it with the same-size regular exhaust pipe and weld that in. That would really do the same thing but probably cost a little more.

That's what I'm planning on doing. That will probably add a little more rasp (but not by much) and it might get a little more boomy in the car. Neither of those should do anything to impair exhaust flow, however. It should improve it, if it's done correctly. I don't know that I'd say it's cost-effective, however, I like what I see in the factory exhaust and unless there is a more cost-effective aftermarket alternative, I'm sure I'll spend the money to do this.

JMO

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Originally Posted by hognutz View Post
what people do is cut the muffler open and take calmps and put them over the perforated section of pipe you see in the picture above. this turns it into as close to stait pipe as you can with the factory system in tact. this is basically like instally cutouts in a way. then you can close the switch to co back to mild exhaust.
I wish I had a picture ready, but a search can show everything I was going to try to show
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Old 03-15-2012, 06:17 PM   #31
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Originally Posted by radz28 View Post
Like hognutz mentions, below, once you're in the muffler, you could use stainless band clamps, and wrap them around the perforated by-pass pipe. This essentially would seal the perforations, and make the muffler nearly 100% "closed" when the valves were open. Others were doing essentially the same, except they'd cut-out the perforated pipe and replace it with the same-size regular exhaust pipe and weld that in. That would really do the same thing but probably cost a little more.

That's what I'm planning on doing. That will probably add a little more rasp (but not by much) and it might get a little more boomy in the car. Neither of those should do anything to impair exhaust flow, however. It should improve it, if it's done correctly. I don't know that I'd say it's cost-effective, however, I like what I see in the factory exhaust and unless there is a more cost-effective aftermarket alternative, I'm sure I'll spend the money to do this.

JMO



I wish I had a picture ready, but a search can show everything I was going to try to show
Thanks all. Are you planning on anything else to go with this? Like hf cats or x pipe?
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Old 03-15-2012, 07:30 PM   #32
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So if the car has dual cats per pipe and the second burn chamber further conditions the exhaust gases why place the oxygen sensor in the middle, wouldn't it be better to be after the last converter?
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Old 03-16-2012, 01:18 AM   #33
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Thanks all. Are you planning on anything else to go with this? Like hf cats or x pipe?

in my case I will go high flow cats with X-pipe. x-pipe just produces better power. Cats cost money but they do reduce fuel smell. I have not figured out why factory uses h-pip still. itis cheaper maybe that is why.
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Old 03-16-2012, 06:43 PM   #34
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in my case I will go high flow cats with X-pipe. x-pipe just produces better power. Cats cost money but they do reduce fuel smell. I have not figured out why factory uses h-pip still. itis cheaper maybe that is why.
I like this set up. Any worries about boost loss?
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Old 03-21-2013, 10:32 PM   #35
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I know this thread is a year old, but what cats are you guys using. I can't seem to get a good answer from Solo if the SS cat will work for sure. All I can get from them is they should, and they don't seem to have anything specific just for the ZL1.
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Old 03-22-2013, 12:11 AM   #36
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I know this thread is a year old, but what cats are you guys using. I can't seem to get a good answer from Solo if the SS cat will work for sure. All I can get from them is they should, and they don't seem to have anything specific just for the ZL1.

Well the JBA catted mid pipes will fit I know 100%. they place I bought my mods from though is trying to talk me out of doing that though say's the cats are not high enough quality.

right now I am contemplating just going catless. I can't make up my mind basically.

I just want some more volume out of the exhaust really. The JBA off road pipes are only $200 so I might just try those for the giggles.

He is trying to talk me into stainles power o/r longtubes for $699.
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Old 03-22-2013, 09:36 AM   #37
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I just purchased Kooks LT 1&7/8 and Kooks green Cats. The headers are at the coaters now. I am going to dyno stock first then dyno after I put the headers and cats on. I will be keeping the factory exhaust. I will post my result. I also am NOT going to tune
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