Cats

[radz28]

It looks to me like the headpipes are pretty similar, and there's an H-pipe in there, but I think an X-pipe would flow a lot more, considering that cross-over size.

Still - it's a great start, IMO. I might knock out one of those cats' on each side though

[Mikes SS]

Same here, I am actually suprised that GM opted to put the second cats on there since they don't serve a purpose and would allow the ZL1 exhaust to breathe a whole lot better!! this exhaust sure looks pieced together, the mid-pipes and the H-pipe sure look like they have way more miles on them versus the rest of it..plus you can see the extra welds in the pipes.

[radz28]

They wouldn't add more expense unless it was necessary...

It used to be, like on '01 Z06s - they first cats' were pup' cats', just to keep the heat high so the primary (lower) cats' would light-off sooner and work more efficiently. This could be the case here, however, I dont' know if there are pup' cats', and actually think the considerable emissions from LSA are probably what is necessary to keep emissions well within check. I don't know how accurate the reports are for LSA, but when you compare it's carbon emissions to other cars - they are quite high. Of course - LSA is considerably more powerful, but it may just be necessary. However - if LS9 can get away with only one pair of cats'...

I maintain GM would add expensive cats' unless it were necessary

[Mikes SS]

That was my thoughts exactly, the ZR1 has one I thought and I just got a new Silverado two weeks ago and it only has one cat per side on it..just don't see the need is all and your right, the cost of those mid-pipes per car is crazy, they could save a buck or two.

[radz28]

Originally Posted by Mikes SS

That was my thoughts exactly, the ZR1 has one I thought and I just got a new Silverado two weeks ago and it only has one cat per side on it..just don't see the need is all and your right, the cost of those mid-pipes per car is crazy, they could save a buck or two.

Maybe - it's perhaps because on the 'Vette (if I recall), the cats' hang right off the manifolds. That may not be possible on 5th Gens because of packaging, and moving them down the distance they have to go as a result may require the secondaries to keep everything efficient All I know, it I could use a little more sound when the valve are open

[hognutz]

Originally Posted by toilets

Can someone provide me some knowledge about converter removal on this car? I thought I read somewhere that removing the cataylitc converters is a very bad idea on forced induction cars because of the heat?

Can someone confirm or deny this?

Yes, I know its illegal but as people have seen in my previous posts, this will be a track car and will not need to be inspected.

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.

[BowtieBelle]

Meow?




























Sorry, that's what I thought when I saw your post title. Back to the thread

[toilets]

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.

[toilets]

Also can someone explain the reason why you have a x-pipe or a h-pipe? Why not just have a straight pipe?

[adamgl]

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.

[toilets]

Originally Posted by adamgl

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.

Thank you

[radz28]

Originally Posted by hognutz

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

Originally Posted by toilets

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

Originally Posted by toilets

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

Originally Posted by adamgl

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

[radz28]

Here's the one pic' I have of the mufflers from 'Vette, just for referrence.

Sorry - back on topic

[toilets]

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?