Eplain NPP please!
Team Owner
Joined: May 2004
Posts: 82,175
Likes: 1,319
From: McKinney TX
St. Jude Donor '21-'22-'23-'24
The exhaust opens up at 3500 rpm to make a louder sound. It stays open as long as the rpms are above that point. The Mild to Wild setups let you determine when it will be open and when it won't.
Le Mans Master
Joined: Mar 2007
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From: Mission Viejo CA
Racer
Joined: Jul 2006
Posts: 486
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From: Bethlehem PA
To my knowledge, there is no difference in EPA ratings between NPP and non-NPP cars.
Burning Brakes
Joined: May 2008
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From: Ottawa Ontario
Team Owner
Joined: Aug 2002
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Tech Contributor
Cruise-In 11 Veteran
NCM Ambassador
St. Jude Donor '05-'06-'07-'10
The NPP is the RPO (regular production option) code for the bi-mode exhaust that is available on the coupe and convertible. This exhaust is modelled after the exhaust on the Z06. The exhaust uses a butterfly valve over one of the exhaust exit pipes (two total, one per muffler) to vary the exhaust output. It works similar to exhaust cut-outs popular on the street rods.
The exhaust control is operated by engine vacuum pressure. The system is tied to the pcm and monitors rpm and throttle position to measure "driver intent".
Under normal circumstances the exhaust valve is closed and it routes the exhaust gas out of the other pipe after it passes through the baffle chamber of the exhaust. In this case it is quieter. If the driver accelerates hard the valves will open at 2,800 rpm as long as the driver is above 80% throttle. Between 30% and 80% throttle the exhaust will open during acceleration at 3,500 rpm.
Here is a diagram of the routing of the exhaust gas and operation of the muffler system.
Here is a graph of the opening and operating characteristics of the exhaust.
The exhaust control is operated by engine vacuum pressure. The system is tied to the pcm and monitors rpm and throttle position to measure "driver intent".
Under normal circumstances the exhaust valve is closed and it routes the exhaust gas out of the other pipe after it passes through the baffle chamber of the exhaust. In this case it is quieter. If the driver accelerates hard the valves will open at 2,800 rpm as long as the driver is above 80% throttle. Between 30% and 80% throttle the exhaust will open during acceleration at 3,500 rpm.
Here is a diagram of the routing of the exhaust gas and operation of the muffler system.
Here is a graph of the opening and operating characteristics of the exhaust.
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Safety Car
Joined: Dec 2007
Posts: 4,974
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From: Magnolia Texas
The NPP is the RPO (regular production option) code for the bi-mode exhaust that is available on the coupe and convertible. This exhaust is modelled after the exhaust on the Z06. The exhaust uses a butterfly valve over one of the exhaust exit pipes (two total, one per muffler) to vary the exhaust output. It works similar to exhaust cut-outs popular on the street rods.
The exhaust control is operated by engine vacuum pressure. The system is tied to the pcm and monitors rpm and throttle position to measure "driver intent".
Under normal circumstances the exhaust valve is closed and it routes the exhaust gas out of the other pipe after it passes through the baffle chamber of the exhaust. In this case it is quieter. If the driver accelerates hard the valves will open at 2,800 rpm as long as the driver is above 80% throttle. Between 30% and 80% throttle the exhaust will open during acceleration at 3,500 rpm.
Here is a diagram of the routing of the exhaust gas and operation of the muffler system.
Here is a graph of the opening and operating characteristics of the exhaust.
The exhaust control is operated by engine vacuum pressure. The system is tied to the pcm and monitors rpm and throttle position to measure "driver intent".
Under normal circumstances the exhaust valve is closed and it routes the exhaust gas out of the other pipe after it passes through the baffle chamber of the exhaust. In this case it is quieter. If the driver accelerates hard the valves will open at 2,800 rpm as long as the driver is above 80% throttle. Between 30% and 80% throttle the exhaust will open during acceleration at 3,500 rpm.
Here is a diagram of the routing of the exhaust gas and operation of the muffler system.
Here is a graph of the opening and operating characteristics of the exhaust.
does the "closing line" indicate that the baffles stay open until a much lower TPS reading is observed then when they open? I have noticed that you can overcome some of the "burble" by maintaining a slight pressure on the throttle but this chart would say that is not true. just curious
Dan
