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I found a set of 3" NPP's from a Z06 that I put on my Grand Sport with LT's and no cats and 3" all the way back. I have the mild to wild and it will make wild when they are open and I'm in aggressive driving mode...... also have an A&A set up with Meth....... I am a fan of being able to close it off when on a trip and the wife is making conversation......
I put this video together just for this topic since I see it come up a lot. Here's some idle, driving both in car and out of car with my npp mufflers. Both open and closed.
Like others I had a home made M2W switch that I almost always left open. Then I got long tube headers with high flow cats. They made the exhaust too loud and droned at cruise, and was too raspy over 4000rpm at WOT. So I installed some little bullet resonators which fixed the rasp at WOT, but didn't do much for the drone. So I installed some little clamps to hold the valves slightly open when in mild mode. Now I mostly use mild mode and am happy with the sound again
Here's a quick and easy way to control your NPP exhaust for about $10 in parts and 10 minutes of your time.
Parts, Tools & Supplies Required: • Mini add a circuit unit • 2 position toggle switch (recommend 20 amp rating) • #16 gauge automotive wire or #18 heavy duty speaker wire {normally I would not recommend using speaker wire for anything but speakers, but since you’re only running a maximum of 10 amps through the circuit the compact design of heavy duty speaker wire has some advantages in terms of a quick clean setup and can easily handle a 10 amp load.} • Small piece of Velcro tape • Black electrical tape • 3 female electrical connectors • 2 male electrical connectors • Wire cutter, stripper, crimper tool • General working knowledge of automotive wiring systems
Step #1 Pull back the carpeted area at the front of the passenger foot box to expose the fuse panel.
Step #2 Using the white fuse puller located at the top of the fuse panel remove the red 10AMP fuse at the lower right corner of the fuse panel as this controls the NPP exhaust.
Step #3 Wire up the mini add a circuit unit and toggle switch as shown in the diagram below. It does not matter which wire goes to which post on the toggle switch. Please note, however, that in order to plug the return wire from the toggle switch back into the mini add a circuit unit you will have to cut the spade of a standard male electrical terminal in half being careful not to cut off too much.
Step #4 Plug the mini add a circuit unit into the fuse panel in the lower right corner where you removed the 10AMP fuse in Step #2 above.
Step #5 Attach the toggle switch to an appropriate spot in the glove box with the Velcro tape making sure that the switch will not interfere with the opening and closing of the glove box AND that the opening and closing of the glove box will not crimp, cut, or gouge the wires going from the toggle switch to the fuse panel. Secure any loose wiring with black electrical tape or similar material.
I really love my NPP muffs and many people have mentioned how good they sound. If you run them with the stock manifolds, they will not be that loud. If you run them with headers and cats, they are quite a bit louder when open. If you run them with headers and no cats, they are allot louder and sound amazing. I did the later. Kooks 1.75 headers w no cats thru used set of NPP. Yes I tied them open as others have suggested at first, but then spent the extra money and added the NPP in a box controller. I think I spent about $600 with used NPP and controller. Best bang for the buck!
Here is a vid of my 10' GS m6 with stock everything short of a k&n intake. IMO not loud at all. Good sound and no drone. Hope this helps.
I love the occasional pop you get between gears with the NPP mufflers. This video highlights it perfectly when you took off.
Side note: When you have the NPP valves closed via the switch, do they open up at all when you are heavy on the throttle? Mine tend to crack open a bit and I'm thinking my vacuum line must be pinched a little bit. I expected them to stay fully closed regardless of throttle position, but there doesn't seem to be enough vacuum to keep them completely closed.
I love the occasional pop you get between gears with the NPP mufflers. This video highlights it perfectly when you took off.
Side note: When you have the NPP valves closed via the switch, do they open up at all when you are heavy on the throttle? Mine tend to crack open a bit and I'm thinking my vacuum line must be pinched a little bit. I expected them to stay fully closed regardless of throttle position, but there doesn't seem to be enough vacuum to keep them completely closed.
If you have an NPP optioned car, then these are the circumstances under which the butterflies are closed or when they are commanded open:
Car is not running, the valves are closed.
Below 30% throttle and 3,500 rpm the valves are closed.
Above 30% throttle and 3,500 rpm the valves will open.
Between 30% throttle and 80% throttle and above 3,500 rpm the valves are open.
Above 80% throttle and above 2,800 rpm the valves are open.
If you have installed a switch (like Mild2Wild, or manual switch) that replaces the EXH MDL fuse, then with the switch closed, the operation should be as above. It's the same as having the fuse in place.
If the switch is open, then the butterflies stay open whenever the engine is running. It's the same as having the fuse pulled. Throttle amount is irrelevant. The butterflies need vacuum to close, not open.
There is no position of the switch that would keep the valves closed under the 'open' conditions above. All of this assumes that all the components are functioned correctly.
Keep in mind that without vacuum, the butterflies stay open. If you have a vacuum leak, the usual symptom of that would be that they might not close completely, or open a bit under acceleration when the vacuum drops even if you don't meet the conditions as described above.
There are little clamps available or one could rig their own up to set the flaps any amount of open they would want regardless of vacuum. Perhaps yours had them?
Love my NPP! American Racing Headers (1 7/8) through high flow cats to the American racing x-pipe...attached to the stock NPP system. Dead pedal switch for the mild-to-wild. Great sound up to 3500rpm...LOUD and racey further on up the revs. Headers and exhaust are all ceramic coated inside and out...with exception to the inside of the cats. This REALLY reduces the heat transfer in the tunnel.
Can be quiet 100% of the time with a vacuum canister and check valve.
Please explain how this works. In the stock set up there's vacuum to the solenoid whenever the engine is running. The solenoid either presents the vacuum to the actuators, or releases it. What is it that the canister would do to change that?
If you wanted the butterflies closed all the time, I'd just pull the fuse and clamp them closed at the actuators. Easy enough to reverse back out. Or pull the fuse and bypass the solenoid with a piece of hose so that there was vacuum to the actuators whenever the engine was running, but that's more work for the same result.
Last edited by FatsWaller; 08-17-2021 at 08:06 PM.
FatsWaller nailed it way better than I ever could but yes, mine will open up on their own with the mild setting selected. Thanks man, i drove the car 170 miles home and made this video before i even pulled in my driveway. So def a rookie take off and pull.
Please explain how this works. In the stock set up there's vacuum to the solenoid whenever the engine is running. The solenoid either presents the vacuum to the actuators, or releases it. What is it that the canister would do to change that?
If you wanted the butterflies closed all the time, I'd just pull the fuse and clamp them closed at the actuators. Easy enough to reverse back out. Or pull the fuse and bypass the solenoid with a piece of hose so that there was vacuum to the actuators whenever the engine was running, but that's more work for the same result.
when you floor the gas, or are in high gear and floor it, going up a hill, or as some say here are over 3,500rpm and some percent of throttle the vacuum goes to zero or near zero and the flaps will open. The vacuum canister stores vacuum so as soon as the vacuum drops the check valve closes holding the vacuum in the canister and lines keeping the flaps closed. Actually after
I shut off the engine my flaps will remain closed for a few hours.
when you floor the gas, or are in high gear and floor it, going up a hill, or as some say here are over 3,500rpm and some percent of throttle the vacuum goes to zero or near zero and the flaps will open. The vacuum canister stores vacuum so as soon as the vacuum drops the check valve closes holding the vacuum in the canister and lines keeping the flaps closed. Actually after
I shut off the engine my flaps will remain closed for a few hours.
This is exactly what's happening to mine. My car did not come with the NPP mufflers, I added them with the "NPP in a Box" to control the actuators. When I have it in "mild" mode, the flaps open up when I really get on the throttle in the lower gears or when I'm going up a hill cruising in the higher gears. I can be cruising at 1200rpm in 6th, give it some throttle to pass someone or go up a hill, and the flaps definitely open up. If I'm just cruising at a constant speed, they'll stay closed and quiet.
when you floor the gas, or are in high gear and floor it, going up a hill, or as some say here are over 3,500rpm and some percent of throttle the vacuum goes to zero or near zero and the flaps will open. The vacuum canister stores vacuum so as soon as the vacuum drops the check valve closes holding the vacuum in the canister and lines keeping the flaps closed. Actually after
I shut off the engine my flaps will remain closed for a few hours.
In the stock setup, the flaps will not stay closed if the RPM and throttle conditions are met regardless of the canister. When the conditions are met, the Exhaust Tail Pipe Flow Valve Control Module gets a command from the ECU, which in turn commands the vacuum solenoid to open, which cuts off the vacuum to the actuators, and spills the vacuum in them. Vacuum is prevented from reaching the actuators. That's the way the system was designed to operate and the canister can't prevent that from happening if it's hooked up at the head of the vacuum line (isn't it?). The design doesn't depend on reduced vacuum caused by engine load. I never noticed the valves opening otherwise because of lack of vacuum, but I don't drive it that much with the circuit enabled.
Edit. To emphasise, for the above to apply, the car needs to have the NPP option from the factory. Aftermarket solutions don't have the same control modules and logic.
Last edited by FatsWaller; 08-17-2021 at 11:31 PM.
Reason: Clarification
In the stock setup, the flaps will not stay closed if the RPM and throttle conditions are met regardless of the canister. When the conditions are met, the Exhaust Tail Pipe Flow Valve Control Module gets a command from the ECU, which in turn commands the vacuum solenoid to open, which cuts off the vacuum to the actuators, and spills the vacuum in them. Vacuum is prevented from reaching the actuators. That's the way the system was designed to operate and the canister can't prevent that from happening if it's hooked up at the head of the vacuum line (isn't it?). The design doesn't depend on reduced vacuum caused by engine load. I never noticed the valves opening otherwise because of lack of vacuum, but I don't drive it that much with the circuit enabled.
Edit. To emphasise, for the above to apply, the car needs to have the NPP option from the factory. Aftermarket solutions don't have the same control modules and logic.
My system is vacuum only, no electrical, I have 100% control of the mufflers. My car did not have NPP from the factory.
08-12-2021, 10:20 AM
