[Chris Edwards]

I'm considering adding 2 resonators where the stock cats were, and also a Magnaflow "2 into 2" dual inlet/ outlet muffler in the rear, just before the rear differential. I had done this with my SS sedan and it's the only way in hell to make things civil when using longtubes, even with the stock NPP system.

[BMWM.D.]

I think my car is more than acceptable with the valves closed in the stock muffler. I do have high flow cats, which probably helps. I feel like it would be way too quiet with an extra muffler. I’d do a set of resonators if you’re catless though.

[Chris Edwards]

Originally Posted by BMWM.D.

I think my car is more than acceptable with the valves closed in the stock muffler. I do have high flow cats, which probably helps. I feel like it would be way too quiet with an extra muffler. I’d do a set of resonators if you’re catless though.

Cats make a HUGE difference. They act as a very effective muffler for each bank of cylinders.

I should have specified that this question was directed towards catless headers.

[GT-ER]

I was JUST going to open a thread on this...lol.

With my OBX LT's, no cats and factory muffler, car sounds tinny and raspy. If I close the valves, the valves rattle. :(

I think some resonators will fix the problem, but don't know what to go with.

[Chris Edwards]

Originally Posted by mdmoore23

I know the stock cats can break down under added power.

That's the reason right there.

[mdmoore23]

Originally Posted by Chris Edwards

That's the reason right there.

Got it. I was just about to change my post to quote yours.

[Can'tHave2MuchHP]

Originally Posted by GT-ER

I was JUST going to open a thread on this...lol.

With my OBX LT's, no cats and factory muffler, car sounds tinny and raspy. If I close the valves, the valves rattle. :(

I think some resonators will fix the problem, but don't know what to go with.

It might help but won't take away the tinny and raspy sound. That's unfortunately how the ZL1 NPP seems to sound after adding Headers/no cats. All of the other GM cars sound good with just Headers/no cats or high flow cats but not a fan of how the 6th gen ZL1 sounds with that setup. If the resonators/extra muffler(s) doesn't fix it, then try a different axle-back/cat-back like Corsa or Borla. Borla gives you valves. Corsa gives you control with your foot. Corsa is only screaming loud at WOT or 80%+ throttle and when is any car with headers quiet with 80%+ throttle? Never.

[Chris Edwards]

Originally Posted by Can'tHave2MuchHP

It might help but won't take away the tinny and raspy sound. That's unfortunately how the ZL1 NPP seems to sound after adding Headers/no cats. All of the other GM cars sound good with just Headers/no cats or high flow cats but not a fan of how the 6th gen ZL1 sounds with that setup. If the resonators/extra muffler(s) doesn't fix it, then try a different axle-back/cat-back like Corsa or Borla. Borla gives you valves. Corsa gives you control with your foot. Corsa is only screaming loud at WOT or 80%+ throttle and when is any car with headers quiet with 80%+ throttle? Never.

You’re right. A V2 CTS-V sounds great with headers/ no cats and stock mufflers. But there’s something about the 6th gen mufflers that clashes with the frequencies of catless exhaust. I’ll surely be swapping to Borla/Magnaflow/Corsa if the mid muffler and resonators don’t dial the sound in to something a bit more pleasing to the ear. Loud is one thing but ZL1 NPP + no cats sounds like a coffee can full of rocks and nails.

[Ricco]

I am LT's into Kooks full decat midpipe into stock NPP. I can't even hear the exhaust while cruising at 50mph, even with the roof down!

Are you sure you dont have your NPP set open all the time?

[IneedAZ]

Originally Posted by Ricco

I am LT's into Kooks full decat midpipe into stock NPP. I can't even hear the exhaust while cruising at 50mph, even with the roof down!

nice to know for when i start my mods

[Ricco]

Originally Posted by Can'tHave2MuchHP

It might help but won't take away the tinny and raspy sound. That's unfortunately how the ZL1 NPP seems to sound after adding Headers/no cats. All of the other GM cars sound good with just Headers/no cats or high flow cats but not a fan of how the 6th gen ZL1 sounds with that setup. If the resonators/extra muffler(s) doesn't fix it, then try a different axle-back/cat-back like Corsa or Borla. Borla gives you valves. Corsa gives you control with your foot. Corsa is only screaming loud at WOT or 80%+ throttle and when is any car with headers quiet with 80%+ throttle? Never.

I like my setup better than Scott’s. He has LT’s into stock midpipe into a Corsa axle back.


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[BMWM.D.]

Originally Posted by Chris Edwards

Cats make a HUGE difference. They act as a very effective muffler for each bank of cylinders.

I should have specified that this question was directed towards catless headers.

I agree they make a difference in volume and tone. That’s one of the reasons I always try to run them if possible. I’d think a set of resonators in the spot where the cats/off road pipes go would produce a similar result.

[Jhunsberger]

Not a ZL1 here, but a Whipple SS. I did cat delete pipes with all stock exhaust and HATED how it sounded, and it was embarrassingly loud. So I did the Borla ATAK system and added in their resonator in the mid-pipe, which is ceramic packed, so it wont over heat like the cats could. I am very happy with the exhaust now, and i am sure the resonator made a big difference.

[Rlhay2]

When I eventually install cat-less long tube headers I intend to run dual x-pipes into the stock muffler to quell the extra noise.