NPP exhaust valves on my SW 3" pipe set

[mike100]

I liked the extra top end power on my recently purchased SW 3" Cat-back, but lets not even try to be diplomatic- it's pretty much loud enough to piss off your neighbors and give you a headache on a long trip.

So I got some C6-Z06 mufflers with the NPP exhaust flapper valves (vacuum actuated).

Note that the inside pipes are the loud, high flow straight thru section. This will be blocked during cruise conditions.



Hacked them off to put them on my loud-*** SW mufflers.



Working out the fit- had to rotate them a touch to fit the vacuum can.
Also the diaphragm comes loose and you can reposition it so the vacuum nipple points in any direction.

[mike100]

Got the staggered tip the same on both sides- sort of follows the fascia curve.

[mike100]

So I finally received the adjustable vacuum switch. When the vacuum controlled secondary throttle is activated on the LT5, so is my loud valve. I set it to 12" of vacuum (12 in Hg).



The switch powers a junkyard EGR vacuum solenoid. This couples the vacuum to the muffler valves. It either connects the vacuum to the valve, or vents the vacuum to the atmosphere thru the little foam filter on the 3rd port. It never has a vacuum leak on the source end. Perfect $8 solution (I should have pocketed it but I was feeling honest). The vacuum source is the nearby vacuum ball used for the a/c and air injection diverter valve. The 12v was easy too- I tapped into the under hood lamps which of course aren't even connected on my car anyhow.


This is actually a second MAP sensor just to monitor the secondary throttle system. I 'T'-ed into it. Vacuum here means all 16 runners and injectors are working on the LT5 and it was a simple idea to switch the NPP valve off of this computer controlled load function.


Here it is idling- the loud section of the muffler is blocked off (left pipe). Will try to get a video on Saturday.

[mike100]

Just in case you missed the picture of the SW muff. One pipe is straight-thru, the other actually muffles:

[XfireZ51]

So whaddya think?

[mike100]

Originally Posted by XfireZ51

So whaddya think?

It's great! Bit of a treasure hunt to get the Z06 mufflers I found. I could leave it well enough alone, but I think I can get faster opening and closing if I run a 2nd vac solenoid and have a dedicated feed to each actuator. Bleed down would have twice the vent capacity.

I do rather like lugging the revs a tad and not droning (at all).

[Paul Workman]

Really interesting setup Mike!

I think I have the jist of what you've done, but pls allow me summarize what I think I understand, and then maybe you can clear up where I "lost your trail".

The adjustable vacuum switch receives vacuum from the "T" connection that also feeds vacuum to the MAP (under the ECM on a 1900 Z). At or below 12" Hg, the switch closes, activating the vacuum solenoid.

Normally, this solenoid connects plenum vacuum to the NPPs - keeping them closed. But, when plenum vacuum drops below 12" Hg, the vacuum solenoid receives its signal and "vents" the vacuum to the atmosphere (through the foam filter), thus relaxing the NPP diaphragms and thus opening the exhaust gates.

Now, if not already, is where I get a little...

You referenced a second MAP, and dedicated vacuum solenoids for each NPP valve. I get the reasoning for the dual system - decreasing bleed time - but I'm missing a link here...

It looks like the vacuum solenoid (pictured) would directly operate the NPPs. But, it is this additional MAP you mentioned, and the electric/vacuum circuitry at the NPP end that has me . I gather the system as it is now is a "work in progress", is it? By that, I mean the NPP end of the setup is yet to be upgraded for individual operation???

As you can see, Mike, I wandered off the path somewhere...

[mike100]

Originally Posted by Paul Workman

Really interesting setup Mike!

I think I have the jist of what you've done, but pls allow me summarize what I think I understand, and then maybe you can clear up where I "lost your trail".

The adjustable vacuum switch receives vacuum from the "T" connection that also feeds vacuum to the MAP (under the ECM on a 1900 Z). At or below 12" Hg, the switch closes, activating the vacuum solenoid.

Normally, this solenoid connects plenum vacuum to the NPPs - keeping them closed. But, when plenum vacuum drops below 12" Hg, the vacuum solenoid receives its signal and "vents" the vacuum to the atmosphere (through the foam filter), thus relaxing the NPP diaphragms and thus opening the exhaust gates.

Now, if not already, is where I get a little...

You referenced a second MAP, and dedicated vacuum solenoids for each NPP valve. I get the reasoning for the dual system - decreasing bleed time - but I'm missing a link here...

It looks like the vacuum solenoid (pictured) would directly operate the NPPs. But, it is this additional MAP you mentioned, and the electric/vacuum circuitry at the NPP end that has me . I gather the system as it is now is a "work in progress", is it? By that, I mean the NPP end of the setup is yet to be upgraded for individual operation???

As you can see, Mike, I wandered off the path somewhere...

Ok, there is some reference to the 2nd MAP sensor- that was meant for another non-ZR-1 forum where people aren't aware of the function of our vacuum secondaries (for those of us who still run them anyways).

To clarify, manifold vacuum closes the muffler flap- they are open at rest.

-To have run the valve straight from the secondary pump would have had the logic 180 reversed- plus they draw too much air and would have messed up the function probably.

So what I did was use the normally open contacts on that adjustable vacuum switch that triggers another vacuum source (through a GM EGR solenoid) when the secondary activates. What it actually does is release the actuator vacuum to the vent(when u step on it) as the solenoid is allowing vacuum through in the off condition (during cruise conditions). It is sort of reverse logic.

The vacuum source is NOT plenum vacuum. it is an is a check-valve isolated source (the vacuum ball under the d/s headlamp.

[-=Jeff=-]

Mike,

you needed the tips as well correct? mind if I ask how much you paid for the NPP mufflers?

I have seen the valves themselves on eBay for about $100 each for new ones

[GOLDCYLON]

Nice thread and a great solution. Dom did you do this electronically or via vacuum like Mike? GC