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Seems like I am always cleaning what appears to be a little bit of dried black liquid drip and dirt off of my outer two exhaust ports/tips, but the two on the inside never get dirty.
When the NPP valves are open (Sport & Track), the exhaust has a direct path through the end pipes. When closed, the exhaust is rerouted like a chambered muffler.
When the NPP valves are open (Sport & Track), the exhaust has a direct path through the end pipes. When closed, the exhaust is rerouted like a chambered muffler.
There is always exhaust going through the inner pipes, but they are connected to perforated pipes inside the muffler cans as depicted by STZ's illustration above. They don't don't get as dirty as the NPP outer pipes (also perforated inside the mufflers) that pass mostly straight through with the valves open. With outer valves closed, most of the exhaust is exiting via the inners, with the outer pipes blocked at the exit point and exhaust contained in the mufflers. That's why it's so much quieter.
I had assumed the inner exhaust pipe are also open and the outer exhaust pipes are used when the NPP valves are open.
Here are cut-away pics to better illustrate the inner-workings of the NPP. Yes, the inner pipes are perforated and always open, but the exhaust flow is muffled. When the NPP valves are opened, the exhaust follows the least restrictive path, which are the outer two pipes...
Seems like I am always cleaning what appears to be a little bit of dried black liquid drip and dirt off of my outer two exhaust ports/tips, but the two on the inside never get dirty.
The reason for the "black liquid appearing stuff" is that is what it is! Water is the main product of combustion. Typically the exhaust is hot enough to have it exit as water vapor-which is what it does in the center tips as they are always open.
The outside tips have a butterfly valve just behind them (look inside you can see it.) It closes at various rpm's depending on Drive Mode setting from about 1700 in Track to ~2500 rpm in Touring. When the valves are closed, some carbon and water can accumulate behind the valve. Under certain conditions (as with cold exhaust pipes) when you accelerate and the valves open that accumulated "stuff" behind the valves comes out and some drips on the bottom of the tip! But the sound is cool!
Here are cut-away pics to better illustrate the interworkings of the NPP. Yes, the inner pipes are perforated and always open, but the exhaust flow is muffled. When the NPP valves are opened, the exhaust follows the least restrictive path, which are the outer two pipes...
Thanks for the pics. Really helped to understand the internals
The NPP is certainly effective, and it’s evident that a lot of R&D went into its design and functionality. Nonetheless, I went with the Corsa set-up... and find that all four tips have an equal amount of soot
The NPP is certainly effective, and it’s evident that a lot of R&D went into its design and functionality. Nonetheless, I went with the Corsa set-up... and find that all four tips have an equal amount of soot
That's what I'm hoping for someday (when I can sneak it past Mrs. DGA3 in our budget)!
This is my experience with an A8 base car with NPP and the Mild to Wild switch installed.
Normally the stock system will close the NPP valves at low RPMs (~1400 to 1800) to eliminate “drone” in sport and track modes. It will also close the valves when “backing down” eliminating the burble.
Activating the Mild to Wild switch is the same as pulling the fuse. In that mode the valves are always open in all modes and that means you will get both drone in the 1400 to 1800 RPM range and also the burble when backing down.
If you go to the top of the CF C7 page you will see a recent "Ask Tadge" question about the NPP exhaust differences between the ZR1 and Z06. His answer is pretty detailed and informative about the NPP exhaust and how it was designed.
The NPP is certainly effective, and it’s evident that a lot of R&D went into its design and functionality. Nonetheless, I went with the Corsa set-up... and find that all four tips have an equal amount of soot
NPP is fine, reminds me of cut-outs "In The Day!"
However Tenneco, who I think is still the Tier 1 Exhaust Manufacturer for the Vette did a fine job considering the cost constraints they were no doubt under! However the Borla mufflers I put on my 1988 Vette and FlowMasters on my S10 truck when between Vettes sounded better, IMO.
I've listened to the several C7 Borla options offered on the Net and a friend had one on his C6 that sounded better than my C6 NPP.
Although I am happy with NPP there are better sounding systems available. Not cheap but a better sound.
Funny, had no idea they started in the natural gas distribution business! Know them as an OEM Exhaust supplier, Walker Muffler, etc.
There were an early customer in VA where they have ~125 MIG welding robots making exhaust systems for car companies etc!
Found this: Tenneco is a multi-national corporation with 93 manufacturing facilities in 26 countries located on 6 continents, with major centers of operations in North America, Europe, Australia and Asia. There were 30,000 employees in 2016.
04-24-2018, 10:57 AM
When are the two inside exhaust ports/tips used?
NPP is fine, reminds me of cut-outs "In The Day!"