Deftly

I have searched this, but nothing really answers what I want to know. I know the exhaust tips have valves that open and close depending on RPM, and then I am not sure. Are there other valves in the system that are normally closed and then open when the RPM is right? Doesn't seem like just opening an exhaust tip would do much. Sorry if this is too basic a question, but I have Goggled this and nothing comes up explaining the full operation. All I get is advertisements for mild-to-wild switches.

Walt White Coupe

Basically there are two outlets from each muffler. The butterfly valve is on the straight thru pipe. When the butterfly is closed it forces the exhaust flow out holes in that straight thru pipe and goes thru the entire muffler circuit to quiet it down. Open the valve and it's straight thru. Only one valve per muffler needed.

AtHomeSoda

MOST people install a control to open and close, ANYTIME... to me IF it only opened at 3300 or 3500 RPM. I would not care for it.. Idle would be church mouse quiet... and basic driving would be quiet ALL the time. With a controller Idle sounds great, and low RPM is also great.

talon90

It is only as a result of butterfly valves at the tips. No other valves are in play.

The 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 valves will be open for the first two seconds that the car is started. It requires time for the vacuum pressure to build to close the valves. After that The operation of the NPP is normally closed, open on demand. Have someone stand behind the car and bring up the RPM to 3,500 and you should see the valves open. The butterfly operation is tied to the throttle position sensor and the RPM. It uses the throttle position to determine driver intent. Under normal operation the valves work as follows.

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.

Thrillhouse

One interesting thing to note is that you need to put a wideband probe on the butterfly outlets if you dyno a car with NPP. When I ran my '08 Z51 the dyno tech couldn't get a wideband reading out of the primary outlet. It read fine until I hit the gas, then it spiked to full lean.

wolfdogs

Talon, awesome as usual.... LOL... you rock.

me......now, no offense to anyone please, just giving my 2 cents... i can't get used to, or believe that an exhaust should have moving mechanical parts.....LOL... thats why i did not order this exhaust and switched mine out to a Corsa Extreme after I got the car. maybe im must from the old school.... LOL

cuts outs are different, but I dont have a need for them.

george vee

When you install a MILD2WILD device to this system you can control the mufflers to stay opened all the time or closed all the time.

laconiajack

Yup, your from the old school! But don't feel bad, most Vette owners are!

RedCruiser

I have had my NPP exhaust for about a month now. I bought a new GS convertible and this is my experience with it.
The baffles will open when 3500 rpms are reached, wether you are driving the car or just pushing on the accelerator, making a real nice throaty sound, again, a real nice sound. So if your just cruising, you will not reach 3500 rpms unless you have a standard transmission, mine is a automatic. So it was just ok when I first bought it.
I am not trying to sell switches, I really dont care if anybody buys one, but for 89.00, it is the best 89.00 you will ever spend.
You hit a remote and the baffles are open, you hit the remote and you shut them off. So if you have an automatic tranny, paddle shift or not, you have this muscle car, throaty sound at all rpms. Hit the accelerator, you will turn heads. I was cruising last weekend around 70 mph on the highway and there is kind of a drone or noise sound when the baffles are open, hit the remote, cant here a thing. This is really noticeable because I have the rag top. I am sure with the hard top, you would leave them open. But again, it is the best of both worlds when it comes to the exhaust system when you have the option of quiet or muscle car.
With the Borla or Corsa I dont think you can shut them off at your finger tips - Please correct me if I am wrong
Hope this helps

Zoxxo

It's either "open all the time" or normal operation as defined above. Never "closed all the time." At least that's the behavior on my Z06 exhaust with the switch.

Z//

AORoads

Good question, Great answer Paul, as usual.

The NPP is very quiet at idle, and at cruising speeds unless you use the "loud" pedal. That's both good and just OK. I've cruised for hundreds of miles per day, and lower noise is good (and less tiring).

But sometimes, a little sound along the way can be good, too. The folks that brought you "mild and wild" tho also made a very small kit to adjust the NPP valves. They can be adjusted slightly open, or up to all the way open. It's all reversible, and you can take it off completely.

The benefits to this method are you can get a little sound all the way thru the rpm range without having to have NPP all the way on, or all the way off.

I started out with the valve open about half way; too loud and drone at some rpm's. I kept adjusting them back until now they're at just the right amount of sound for me! I hear it, it's perfect for me. Hey! It works!

Just another great product for the Vette. Since the etailer isn't a vendor, email me if you want to know where, etc.

Swiftrider08

Old school? Well then you should remember the spring loaded heat riser butterfly valves that were mounted on the exhaust manifold of just about every car out there that had a heat tube from the exhaust manifold up to the choke pull off. They were even still used when the choke tubes went away as a way to keep heat in the heads so the engine would warm up faster.

I am only 49 and remember all that stuff! Moving parts in the exhaust stream is what is old school.

CH-Z51

Somethings wrong with your M2W. Mine stay in the open all the time or closed (which would be normal) position all the time, depending on how it's switched.

AtHomeSoda

What he said...

Thrillhouse

That's not really possible. The M2W systems just switch power to the exhaust control computer. It's the equivalent of inserting and removing the exhaust fuse as you drive along. When the exhaust system has power the ECU controls the butterflies exactly like it normally would with the fuse installed. Thus they stay closed at low throttle condidions and open when you punch it.

The only way to make them stay closed permanently would be to replace the normal exhaust logic in the ECU or add your own control module and a vacuum reservoir to replace the manifold vacuum source from the control computer.

talon90

Correct, NPP in a box can do it because it supplies it's own vaccum source, M2W can't because and the end of the day the NPP or Z06 dual mode requires vacuum to keep the valves closed and at 3,500 RPM whether you like it or not the vacuum goes away due to the progamming and as such, the valves can't stay closed.

Deftly

Great discussion. Thanks to all who participated and those who will.

Shortimer

Thrillhouse,
I had this happen to me last Saturday. The first dyno run the exhaust probe was inserted in an outer port. For the 2nd run the tech changed the location to an inner, valved port and the run was much better, more power.

Zoxxo

Nope. The M2W, and all other variants of this technique, merely replace the fuse with a switched line. Turning the thing off merely reverts to the stock system/logic. At no point do they "stay closed all the time."

And I don't have an M2W anyway. Rather than pay $90+ for the thing I went to the auto parts store and got a fuse extender, some wire and a switch. About $16 if I remember correctly. I manage to survive without having to activate it by a (and find a place in the cockpit for a) remote control.

Z//

AtHomeSoda

If you ADD NPP to a car that never had NPP from the factory, and you use Mild 2 Wild IN A BOX, it connects to a vaccum source, and you CAN keep Open or Closed ALL the time... I know, cause that is what I have.. Love it, WAY better than having it open on RPM... Stealth when you want, or wild.. up to you...