Npp exhaust question - Page 2 - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

ZMEnow · 05-19-2021, 12:36 PM

Quote:

Originally Posted by Dega Man

The exhaust valve is only closed between around 2100 rpm's to around 3000 rpm's otherwise it is open.

Actually it is closed/open based on available vacuum not RPM's thus at a cold start there is less vacuum to help in warming the CAT's. After the car is warm they remain closed on subsequent starts at idle.

larry_g · 05-19-2021, 12:57 PM

Quote:

Originally Posted by ZMEnow

Actually it is closed/open based on available vacuum not RPM's thus at a cold start there is less vacuum to help in warming the CAT's. After the car is warm they remain closed on subsequent starts at idle.

I'm going to have to disagree on this. There's a vacuum storage system, because I can close the flaps before starting the car.

ZMEnow · 05-19-2021, 02:39 PM

Quote:

Originally Posted by larry_g

I'm going to have to disagree on this. There's a vacuum storage system, because I can close the flaps before starting the car.

Not sure what you are disagreeing with. I didn't say there was no vacuum, I said it is controlled.

larry_g · 05-19-2021, 04:55 PM

I'm just saying that the reason they are open at idle is due to programming and not available vacuum. Even with the car sitting over the weekend, I can flip my switch and hear the flaps close before I start the car.

If I remember correctly, the stock programming has them always open at idle, then they are open or closed based on rpm, speed, and throttle position.

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Genob4c · 05-19-2021, 09:25 PM

I'd like to know more about this setup. Can you point me to the details and instructions? Thanks.

Quote:

Originally Posted by larry_g

I thought it was pretty easy. There was a good writeup here with a wiring diagram.

Basically you break the line from the FPCM to the fuse block and run it through a three position switch (probably similar to M2W.

One position is open, same as fuse pull. One position is closed, same as normal operation. And one position goes to ground, full closed.

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larry_g · 05-20-2021, 06:32 AM

Quote:

Originally Posted by Genob4c

I'd like to know more about this setup. Can you point me to the details and instructions? Thanks.

This is the post I referenced...

https://www.camaro5.com/forums/showthread.php?p=7584544

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12oclockshadow · 05-20-2021, 11:00 AM

Quote:

Originally Posted by larry_g

This is the post I referenced...

https://www.camaro5.com/forums/showthread.php?p=7584544

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Well that is alot easier. Assume this will work on a ZL1 models as well?!

RobZL1 · 05-20-2021, 12:17 PM

Quote:

Originally Posted by 12oclockshadow

Well that is alot easier. Assume this will work on a ZL1 models as well?!

Sure does!

Genob4c · 05-20-2021, 07:35 PM

Thanks very much!

Quote:

Originally Posted by larry_g

This is the post I referenced...

https://www.camaro5.com/forums/showthread.php?p=7584544

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ZMEnow · 05-21-2021, 11:17 AM

Quote:

Originally Posted by larry_g

I'm just saying that the reason they are open at idle is due to programming and not available vacuum. Even with the car sitting over the weekend, I can flip my switch and hear the flaps close before I start the car.

If I remember correctly, the stock programming has them always open at idle, then they are open or closed based on rpm, speed, and throttle position.

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The Fuel Pump Control Module receives accelerator pedal position, transmission gear and RPM information via serial data from the engine control module. The Fuel Pump Control module uses that information to determine a target position for the exhaust valves. To achieve the target position, the Fuel Pump Control Module commands the Exhaust Flow Control Valve Relay On or Off.

When commanded On the Exhaust Flow Control Valve opens the Exhaust Flow Control Valve Solenoid which exposes the left and right tailpipe exhaust valves to vacuum. When exposed to vacuum the tailpipe exhaust valve will close. When commanded Off the Exhaust Flow Control Valve Solenoid closes the Exhaust Flow Control Valve Solenoid which isolates the left and right tailpipe exhaust valves from vacuum. In the absence of vacuum the tailpipe exhaust valves will open. This is the reason I stated its controlled by vacuum. The ECU takes the data for a cold start and removes vacuum, but I believe as it warms it it applies vacuum unless the other metrics mentions above are met then the ECU also applies vacuum.

I am two weeks away from changing oil, trans fluid, rear end fluid, brake bleed, and the front two struts. Since I will have it on the lift for the day in the garage I will check the valves after warm and report.

CJ27 · 05-21-2021, 02:27 PM

Quote:

Originally Posted by larry_g

True, NPP is open at idle. That's why I put in a three way switch so I can go full closed at startup early in the morning.

It really should be this way from the factory. The Corvette is. It would be nice to be able to adjust it with custom tuning as well.

larry_g · 05-21-2021, 03:53 PM

Right, I misunderstood what you were referring to...they are vacuum operated but controlled electronically. Different ways to say the same thing.

I don't recall mine ever being closed at idle but it's been a long time since I ran in the stock configuration. It'll be interesting to see what it does.

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Brutale arancia · 05-22-2021, 08:38 AM

Quote:

Originally Posted by ZMEnow

The Fuel Pump Control Module receives accelerator pedal position, transmission gear and RPM information via serial data from the engine control module. The Fuel Pump Control module uses that information to determine a target position for the exhaust valves. To achieve the target position, the Fuel Pump Control Module commands the Exhaust Flow Control Valve Relay On or Off.

When commanded On the Exhaust Flow Control Valve opens the Exhaust Flow Control Valve Solenoid which exposes the left and right tailpipe exhaust valves to vacuum. When exposed to vacuum the tailpipe exhaust valve will close. When commanded Off the Exhaust Flow Control Valve Solenoid closes the Exhaust Flow Control Valve Solenoid which isolates the left and right tailpipe exhaust valves from vacuum. In the absence of vacuum the tailpipe exhaust valves will open. This is the reason I stated its controlled by vacuum. The ECU takes the data for a cold start and removes vacuum, but I believe as it warms it it applies vacuum unless the other metrics mentions above are met then the ECU also applies vacuum.

I am two weeks away from changing oil, trans fluid, rear end fluid, brake bleed, and the front two struts. Since I will have it on the lift for the day in the garage I will check the valves after warm and report.

Yeah but do you have any real proof or perhaps a detailed accurate explanation for your "opinion"?

Dega Man · 05-22-2021, 01:15 PM

Quote:

Originally Posted by ZMEnow

Actually it is closed/open based on available vacuum not RPM's thus at a cold start there is less vacuum to help in warming the CAT's. After the car is warm they remain closed on subsequent starts at idle.

You could be correct I could be mistaken, I have the service manuals if I remember correctly I thought it was just based on rpm. I will look over the service manual again to verify.

05-19-2021, 04:55 PM	#18
larry_g Drives: 2014 1SS/1LE Join Date: Nov 2015 Location: Louisville, KY Posts: 826	I'm just saying that the reason they are open at idle is due to programming and not available vacuum. Even with the car sitting over the weekend, I can flip my switch and hear the flaps close before I start the car. If I remember correctly, the stock programming has them always open at idle, then they are open or closed based on rpm, speed, and throttle position. Sent from my Pixel 5 using Tapatalk __________________ 830 WHP 700 WTQ, Whipple 2.9 @ 13lbs Boost, Flex Fuel Tune by Blevins Tuning, LSA SBE, 3.5 GripTec, ATI LS3 Damper, AFR 260cc Mongoose, ARP Studs, Yella Terra Ultralites, Johnson 2110R, BTR PDS Stage 3, Melling 10355, Improved Racing Baffle, ID1050X, DSX Triple Fuel Pump, RotoFab CAI, NW 103mm TB, Stainless Works 1-7/8" LTH to 3" Speed Eng w/ X-pipe to NPP, Powermaster 9509 XS, Detroit Speed Motor Mounts, MGW, Monster LT1-S, ZL1 Calipers, DBA Rotors & Pads, Bilstein B6 Struts & Shocks, BMR 1.25" Drop Springs & Adj Rear Bar, Pegasus Solid Bushings, Z/28 Wheels, other misc parts.

05-21-2021, 03:53 PM	#26
larry_g Drives: 2014 1SS/1LE Join Date: Nov 2015 Location: Louisville, KY Posts: 826	Right, I misunderstood what you were referring to...they are vacuum operated but controlled electronically. Different ways to say the same thing. I don't recall mine ever being closed at idle but it's been a long time since I ran in the stock configuration. It'll be interesting to see what it does. Sent from my Pixel 5 using Tapatalk __________________ 830 WHP 700 WTQ, Whipple 2.9 @ 13lbs Boost, Flex Fuel Tune by Blevins Tuning, LSA SBE, 3.5 GripTec, ATI LS3 Damper, AFR 260cc Mongoose, ARP Studs, Yella Terra Ultralites, Johnson 2110R, BTR PDS Stage 3, Melling 10355, Improved Racing Baffle, ID1050X, DSX Triple Fuel Pump, RotoFab CAI, NW 103mm TB, Stainless Works 1-7/8" LTH to 3" Speed Eng w/ X-pipe to NPP, Powermaster 9509 XS, Detroit Speed Motor Mounts, MGW, Monster LT1-S, ZL1 Calipers, DBA Rotors & Pads, Bilstein B6 Struts & Shocks, BMR 1.25" Drop Springs & Adj Rear Bar, Pegasus Solid Bushings, Z/28 Wheels, other misc parts.