PowerLabs

Video Here

The stock Corvette exhaust is way too quiet, and aftermarket mufflers are too expensive, too heavy, or too loud... Fortunately for us Chevrolet saw it fit to retrofit some of their vehicles with the clever NPP Bi-Modal exhaust that is loud when you want it, but quiet when you don't... Here is the easiest, quickest, cheapest way to get the NPP action in a car that was not fitted with it in the first place.

First you need NPP mufflers, of course. I bought a pair of C6 Z06 mufflers for about $350 and run them with my Kooks 1 3/4" headers and a 3" catted X-Pipe. Before them I ran GHL exhaust (intolerable drone), then Corsa Sports (raspy, and 22lbs heavier than the GHLs). Before today I was running them open all the time, and the drone was really starting to get to me.

For this, all you need is:

16 feet of 5/32" rubber hose ($15)
2 3/16" vacuum "T"s
1hour or so of your time

First connect the two butterfly actuators via a rubber hose into a 3/16"T". Make sure to loop the hose between the bumper beam an the muffler bracket, so it does not hang down:



Use zip ties to make double sure that these hoses can not pop off. You will have a vacuum leak if they do:



Connect a 15 foot long hose to the T, and loop it through the frame, heading into the rear driver side wheel well:



Loop the hose around the fuel tank filler line, then down towards the drivers side door sill. This ensures that the hose stays flush with the wheel well. N/A cars won't have the red Boost-A-Pump there, but fitment is the same:



Use a wire, or something similar, to snake the hose on to the front drivers side wheel well, then up along the windshield washer reservoir, and out by the brake booster:



"T" into a vacuum line and connect this line into it. Because of my supercharger kit, my brake booster line is "T"ed for the blow off valve and the Kenne Bell Boost a pump pressure sensor; I simply tied it in there.



THAT'S IT!!! $25 and about an hour of easy hose routing...
Now, how does it work?
It is very simple: The muffler butterflies are actuated by engine vacuum; when there is vacuum on the intake manifold, they close, quieting the muffler down. When the intake manifold vacuum goes away, they open, making the car loud.
Engine vacuum is proportional to throttle opening; open throttle = no vacuum (or boost in my case), closed throttle = vacuum.

On engine startup, they are open; the engine comes to life with them on loud then they close up and the car quiets down a split second later.
On cruise control, or light cruise, they are closed.
Around 50% throttle they begin to open progressively, and the car becomes louder with increasing throttle application.
Around 75% throttle they go full open an the car is as loud as it is going to be.

Want them open all the time? No problem: just pull the muffler hose off the "T" and cap it off:



Or simply crimp the line so the vacuum can't pass through

Here is a quick video showing the mufflers in action:

http://www.youtube.com/watch?v=1nx3nmWapgw

PowerLabs

Here is what I like and what I dislike about this system:

Dyno testing shows that a supercharged C6 stands to lose as much as 40HP+ with the butterflies closed. For me, a simple system that has them all open or all closed is not acceptable because I need them fully open no matter what when I go full throttle, otherwise exhaust backpressure will be excessive.

PROS:
Car starts up with them open, all the time. I wouldn't want it any other way.
Butterflies are always open at high throttle settings, so the mufflers never restrict engine horsepower when I am trying to make power.
Light cruise is now QUIET!!!
No drone!
No need for me to do anything; they open when I want power, they close when I drive mildly.
Simple, light, reliable system.
CHEAP!

CONS:
Deceleration burble is just about gone, since the mufflers are always closed on decel, no matter what.
I have to get out of the car if I want them open all the time.
My car is supercharged, so at WOT, I am actually applying pressure to them.. I believe they will be OK with that, but that remains to be seen.

Overall I am very happy with the way it worked out, and just wanted to share it with the forum... Enjoy!

3 Z06ZR1

Nice job! The easy way, for sure the cheapest!

PowerLabs

Yup, your post on power lost and gained with the butterflies open and closed inspired me to do this

carlrx7

i have the same setup,, but i used 3mm high temp vacuum tubing. love it!! around town i cap the line.. for long highway trips i hook it up..

-carl

PowerLabs

Oh man, and here I was thinking this was my original idea
Your car is N/A, right... How quickly do your butterflies open? I've noticed that mine open very fast and at relatively low throttle settings; I wonder if you need to be near WOT with an N/A car for that to happen?
My tubing works out to almost 4mm btw.

PowerLabs

I just made a new video today that does a much better job of illustrating how the system works, and how quickly the flappers move... Enjoy:

http://www.youtube.com/watch?v=nhL6Y...e=channel_page

Pipedreams

Nice job on the install and the write-up. I assume you have a supercharged car? We did some work on this type of system last year and found although it might appear the open when you blip the throttle, on a normally aspirated car this does not work on the road. Even nailing the throttle on the road only caused them to break open but close up almost instantly. We did a ton for on the road test and just found this did not achieve what we were looking for and they were shut 99% of the time. I ask about the supercharger because your results may be much different because of the reduced vacuum. Also just my opinion but I would not tap off the brake booster line, a failure may cause you not to be able to stop.

PowerLabs

Thank you Yes, my car is supercharged, and I am sure that has a lot to do with how quickly the flappers snap open when I get on the gas; I have observed that on the road anything over maybe an inch of gas pedal travel and they open right up... When I leave a light or a stop sign they are pretty much open constantly, then once I have reached the speed limit and ease of the gas they close up... Its perfect! I was wondering how it would work in an N/A car, guess you would be the guy to know that
You can see on my video that both butterflies will go fully open in less than a second as early as 2000RPM.

Regarding tapping the brake line: I'm not very fond of it either. A major leak there would cause loss of the brake vacuum assist, but that would hardly make the car impossible to stop; I have yet to see a single race car or rally car that has boosted brakes, and they don't seem to have a problem. My prevention here is to put everything together carefully, zip tie the connections and route the lines around safe places; I do not antecipate any leaks.

My decision to tap the brake line was very simple; the Supercharger kit has it tapped already for the Blow Off Valve actuator AND the Kenne Bell Boost-A-Pump sensor line... I just added another "T" in there when I couldn't find a better source... That said, if you have a better idea, I am all ears !

Thank you for your input BTW; I really like your products
A question if I may; have you ever seen or heard of issues with those diaphragms when they see boost? I'm running 10PSI and the seem allright so far.

Pipedreams

Thanks. No issues with boost, I am surprised how easy they open for you as they require only 11HG to close, but I am sure it has to do with the blower. I also think your hose size might have something to do with it as I use 7/32". Keep up the good work and if I can help let me know.

AndrewZPSU

Anyone try putting a valve before the T? This might help for an NA car as well.

If you wanted to run on/off you keep the valve open. (Not sure how well this works on N/A)
If you wanted to run closed you start the car, then close the valve.*
If you wanted to run open you close the valve before you start the car.

*Not sure if the closed 100% of the time will work.... but this might be a lot better than capping stuff off.

I am probably going to try this sometime this week.

Pipedreams

Having close to 3yrs hands on with these systems IMO most want the exhaust open at idle and during mild acceleration which running a system like this (especially on a N/A) does not do.

The idea of adding a valve before the "T" and closing it prior to starting will keep them open 100% of the time. Shutting the valve after opening will only keep them closed for a short period of time and then they will just creep open as the available vacuum bleeds off (we have tested this, generly takes 15-30 minutes). We also found you will get "chatter" of the flaps without the proprer vacuum levels to keep them shut.

The system I make does what most want, 100% open and with the press of the wireless button 100% closed, allowing you to start it up in either setting. It's nice to see some alternatives

AndrewZPSU

I'm still waiting for the all electric stuff and this is going to be my alternative for the moment. Can't wait for no vaccum lines!

Pipedreams

Actually we worked with B&B last year on a full electric system, they rejected it for a number of reasons. I Mainly without expensive controls you had no idea of the position of the flaps and they were concerned about the reliability. On the NPP's there is almost no audible difference between 1/4" open and full open so the product was dropped. was lucky enough to work with the engineer that designed the corvette bimode system and he made it clear why vacuum was the best choice., let us know how you make out

AndrewZPSU

I'd like to learn more why vaccum is the best choice, maybe you can pursuade me. I really just don't want to run the lines lines, but it seems like I'm going to do it anyway.

How much vaccum is actually needed and why would running the line such as this not work the same as a car equipped with the NPP exhaust? Isn't it the same vaccum source, and doesn't it drop the same way?

Thanks.

(Sorry to hijack thread)

Pipedreams

Not trying to persuade, just trying to educate, PM sent

greekc6

ttt