[Eldi Z]

Can anyone elaborate on the following:

1.) Difference between the "NPP" and the "Regular" SS system?

2.) Difference between the SS /1LE (if any difference to the "regular" SS?) "NPP" and the ZL1 "NPP" ?

Trying to learn stuff about my new 1LE

[Juiced1]

The NPP system has an active valve that will open and close at certain rpms kind of like a cut out. They keep the car quiet while cruising and give more volume when you are on the throttle. So it's basically a muffler bypass or a bi-modal muffler. One side of the muffler is a straight through pipe for maximum volume and performance and the other half is a very tame muffler. The standard SS exhaust with single tips on each side is a basic exhaust system that keeps the car way to quiet imo.

[Eldi Z]

O.K., thanks.
What about ZL1 stock system, compared with the SS "NPP" ? Any significant differences between the two?

[Boost Creep]

The ZL1 tips appear to be bell mouthed compared to the 1LE/SS NPP tips.

[JamesNoBrakes]

When you start it, it's like a bomb goes off.

[Casalino]

I want more sound from my npp. I plan on keeping the mufflers with the bypass valve.....possibly change something between the mufflers and the engine. What are my options? I want the car to pass inspections and have no dash lights triggered

[Alpha1BC]

Originally Posted by Casalino

I want more sound from my npp. I plan on keeping the mufflers with the bypass valve.....possibly change something between the mufflers and the engine. What are my options? I want the car to pass inspections and have no dash lights triggered

Simplest options are to get an aftermarket system that still has NPP valves or cutouts.

Aftermarket systems will keep all the functionality that the current system has, but both open and closed modes will be louder than they are with the stock system. You'll also likely get a different exhaust note that will be unique depending on muffler manufacturer.

Cut-outs are simply another set of valves that you install somewhere else on the system, typically somewhere between the cats and muffler. These will give you a 3rd "mode" that is louder than the open dual mode system, but will require you to install some form of additional wiring to be able to open and close them. Might also sporadically get codes for cat efficiency depending on what conditions you open them with since the flow restriction of the mufflers is gone when the cutouts are open.

[davef]

Originally Posted by Casalino

I want more sound from my npp. I plan on keeping the mufflers with the bypass valve.....possibly change something between the mufflers and the engine. What are my options? I want the car to pass inspections and have no dash lights triggered

I recommend simply having an exhaust shop cut out the secondary cats and replace them with a plain section of pipe. Many members here have had that done including myself. It added a bit of volume and more popping on decel. Plus it was super cheap. My shop only charged me $100! But I've seen members here pay up to $200 at their shops. Still worth it.

I want to add that I have no lights on the dash. If the weld is done correctly you won't have any codes but if there is a leak some people have seen codes because the primary cats are very close to the secondary ones and their sensors detects the leak. Of course if you have a visual inspection in your state you probably can't get away with this. My state doesn't.

[ST1LE]

Originally Posted by davef

I recommend simply having an exhaust shop cut out the secondary cats and replace them with a plain section of pipe. Many members here have had that done including myself. It added a bit of volume and more popping on decel. Plus it was super cheap. My shop only charged me $100! But I've seen members here pay up to $200 at their shops. Still worth it.

I want to add that I have no lights on the dash. If the weld is done correctly you won't have any codes but if there is a leak some people have seen codes because the primary cats are very close to the secondary ones and their sensors detects the leak. Of course if you have a visual inspection in your state you probably can't get away with this. My state doesn't.

This is good advice, I will add if possible to use your suggestion with clamps as to reverse when inspection time comes.

As you point out, there are solutions, but they take some work to get around tuning and inspection.

[Eldi Z]

Back to the question about the differences between the SS NPT and the ZL1 system.
Apart from the different sound, is there a difference in flow / performance / diameters / muffler and/or CAT designs and materials?

Another piece I forgot to ask about are the headers: SS NPT system headers Vs. ZL1 headers?

What I am getting at is: If I happen to install a power adder I.E. PD or Centri charger, is the SS NPT system overall going to perform / flow like the stock ZL1's?

Talking about the same power levels of ~ 650 crank-HP (as the ZL1 has stock).

[Ecchi667]

Originally Posted by Eldi Z

Back to the question about the differences between the SS NPT and the ZL1 system.
Apart from the different sound, is there a difference in flow / performance / diameters / muffler and/or CAT designs and materials?

Another piece I forgot to ask about are the headers: SS NPT system headers Vs. ZL1 headers?

What I am getting at is: If I happen to install a power adder I.E. PD or Centri charger, is the SS NPT system overall going to perform / flow like the stock ZL1's?

Talking about the same power levels of ~ 650 crank-HP (as the ZL1 has stock).

I'm not certain of this, but I *think* the SS exhaust system is 2.25" and the ZL-1 exhaust system is 3". Other than that, it's the same system.

All forced induction kits are designed to work with the stock system. A more free-flowing exhaust system will allow more power gains if you were to mod further, however quoted output by vendors is with the stock exhaust and - as far as I know - it isn't a limiting factor at those levels. In other words, you should be just fine doing FI first and then when you want more power still, upgrade the exhaust at that point.

[Eldi Z]

Thanks for the quick reply!
This is what I thought, but out of interest wanted to know the differences to the ZL1 stock piping / headers and materials (mufflers, CATs, Etc.)

[JeromeS13]

Originally Posted by Ecchi667

I'm not certain of this, but I *think* the SS exhaust system is 2.25" and the ZL-1 exhaust system is 3". Other than that, it's the same system.

All forced induction kits are designed to work with the stock system. A more free-flowing exhaust system will allow more power gains if you were to mod further, however quoted output by vendors is with the stock exhaust and - as far as I know - it isn't a limiting factor at those levels. In other words, you should be just fine doing FI first and then when you want more power still, upgrade the exhaust at that point.

That is not correct. Both systems have 2.75" piping.

[Eldi Z]

Originally Posted by JeromeS13

That is not correct. Both systems have 2.75" piping.

So is it safe to assume that the SS "NPT" and ZL1 stock systems are similar in the performance and overall flow (Incl. the headers and all the way to the rear mufflers?