[oldman]

Originally Posted by Atomic Ed

I'm thinking the same thing Oldman. Considering shorties and a primary cat delete since I see no real advantage on the ZL1 exhaust system

Do you think moving the secondary O2 sensors to behind the secondary cats will work? Not sure if the freer flowing secondary cats will suffice to keep the secondary O2 sensors happy.

To my mind the only potential problem is the second cats especially with larger more surface area Hooker shorties will take 30 seconds longer to light-off and there is a potential in cold weather and light throttle driving after start up to trigger a cat inefficiency light. This is a common problem with most new cars that have a pup cat / primary cat system that is replaced with a larger free flowing exhaust. The problem is self correcting but people freak out anytime the get a check engine light.

I would have gone with ST and front cat deletes myself but I felt that LT would help in the mid range as I have a MSD and a M6. I intend to do cam and heads one day.

For an auto, or for somebody with no intention to move to cam / heads. I would be that ported stock IM, ported TB, aftermarket or slightly cleaned up factory headers and primary cat deletes would be the way to go. Especially now that we know even GM has pronounced the stock system good to 650 HP. Lingenfelter does NOT change the headers and exhaust with their "base" package(s). I use the term loosely as Ligenfelters base goes from mild to crazy. Aslo factory header is similar to the Z/28 at 505 HP and I believe the hot LT1's 535 rating is based on factory header if not the whole factory exhaust.

For the primary cat deletes. You do lose the front hanger that bolts to the front cat. I would fab a new set of hangers as that is a BIG exhaust and there is introduction of false knock. I would probably install a stainless steel flex pipe in one of the front cat deletes (only in one leg probably driver's side). This will break up any resonance / oscillation in the exhaust.

[Atomic Ed]

Thanks for the feedback Oldman. If I understand you right, I should only get a temporary CEL until everything heats up, correct? I can live with that.

This is only a temp solution. I'll eventually get a new tune and just dial the back sensors out. And thanks for the tip on the front hangers. Just gotta crawl under there and figure out a new hanger setup before I dive into this.

And as another indicator of how effective the stock exhaust is, Redline did use LTs on there 1200 hp build, but left the NPP muffler in place. So STs and front cat delete should do just fine for my target of 625 rwhp with a PD.

[oldman]

yep and IMO of course LT less useful I'd either run stock or Hooker STs you target HP is low enough.... Rotofab deffinetly showing more bang for the buck on a base supercharge build IMO.

[Atomic Ed]

You read my mind Oldman. Hooker STs and the front cat delete. I'm going for a DD. Don't need every ounce of hp. I'm going for a more balanced approach (for a change).

Stay under 625 rwhp so I can maintain the stock fuel system and keep the exhaust tone down so I can go wine tasting on the weekends and not draw attention.

No meth injection. Been there, done that. The girlfriend runs the meth tank dry, fries the pump and then it's a tow back home, again.

[suzook]

The zl1 has a bigger rattle too

[jimmypop13]

I bought a cheap zl1 exhaust to put on my SS. I already have SW headers and full x-pipe so I just wanted the muffler for the bigger tips so I cut it 6" from the muffler. I don't know if there's packing in the muffler or not but even though they look identical other than the tips, I swear there was a slightly different tone and it was just a touch quieter. Mine had 9k miles and the ZL1 had around 1k. Not sure that would make a difference even if there was packing material.

[jdasnt3]

My friend's ZL1 certainly sounds very different than my SS with NPP on start up.

[jimmypop13]

Originally Posted by jdasnt3

My friend's ZL1 certainly sounds very different than my SS with NPP on start up.

In what way?

[Atomic Ed]

Another data point. I asked a ZL1 owner to measure the ID on the stock header collector. The ID is the same between the SS and the ZL1.

[nicktechla]

I thought the ZL1 had 3" inlets on the muffler, but the SS is like 2 3/4? Because there was someone on here with an SS in another post that got a 3" full length setup and it was too big for the factory muffler. I'll see if i can find the post

[jimmypop13]

Originally Posted by nicktechla

I thought the ZL1 had 3" inlets on the muffler, but the SS is like 2 3/4? Because there was someone on here with an SS in another post that got a 3" full length setup and it was too big for the factory muffler. I'll see if i can find the post

I have both full systems to an ss and zl1 sitting in my backyard. 2.75" on both.

[oneredry]

the muffler is the same. The tips and the manifolds are slightly different with different GM part numbers.

[jimmypop13]

I looked at my SS and ZL1 muffler today. These numbers are on the actual muffler. Not sure if this proves the mufflers are different internally or if this is just a unique serial number. I just know I feel like the zl1 muffler sounded a little quieter on my car. Maybe it's just in my head or the difference between 9k miles on my SS muffler and 2k miles on my zl1 muffler. I guess it would kinda make sense if they were different internally. The ZL1 with a supercharger and more power is going to be louder. Maybe they had to quiet it down to meet dB restrictions. Or the perceived sound difference could just be in my head

ZL1 NPP in first pic, SS NPP in second pic

[jimmypop13]

Just saw these clips on a TV show of them swapping the internal portions of the muffler for testing. Pretty cool