NPP exhaust valves on my SW 3" pipe set

[GOLDCYLON]

Originally Posted by BigJohn

Have you ever heard Callaway Megaphones!!!

What? I cant hear you and im bleeding from my ears.

[WARP TEN]

Originally Posted by ZZZZZR1

Question

Could you add the npp and the mild to wild switch? With mild to wild you can press a button to open and close the exhaust Possible? Thanks
David

Hi David--That's what I have with the electric cutouts. Stock system for quiet (well, a little louder than stock with headers and no cats) but then I can open up the cutouts all the way to a complete straight through system. Very loud. What I have been doing is running with the cutouts cracked just a little bit to add some rumble. Quite livable. But it is fun when they are wide open. -Bob

[ZZZZZR1]

Originally Posted by WARP TEN

Hi David--That's what I have with the electric cutouts. Stock system for quiet (well, a little louder than stock with headers and no cats) but then I can open up the cutouts all the way to a complete straight through system. Very loud. What I have been doing is running with the cutouts cracked just a little bit to add some rumble. Quite livable. But it is fun when they are wide open. -Bob

Bob

You have Corsa and electric cut outs too??

Ohhhhhhh. Details please!!!!

Love these modifications!

Cheers

David

[Paul Workman]

Originally Posted by mike100

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.

OK, I got a clear picture now.

Your approach is interesting, and I suspect has very "digital" (read: either ON or OFF!) characteristic, compared to the direct vacuum line from the plenum to the NPPs (i.e, the FBI approach).

Simple and elegant vs. complex and wonderful?

I don't have a feeling either way, far as which is a better solution. From a simplicity view, the FBI approach is as simple as it gets. However, I think your method has potential to sharpen the NPP operation considerably - especially if dual, electrically triggered solenoids were used; one each for each NPP were to be employed.

Yours is an interesting approach, "fer sher". Thanks for sharing!!

[Paul Workman]

Originally Posted by ZZZZZR1

Bob

You have Corsa and electric cut outs too??

Ohhhhhhh. Details please!!!!

Love these modifications!

Cheers

David

Bob posted a picture of his electrically controlled cutouts a while back - located in place of the elbows behind the differential. The open gates open straight back, and when closed the cutout valves angled outlet point in the direction of the port/starboard mufflers; the only way to go with the single outlet Corsa muffs.

[Paul Workman]

Originally Posted by -=Jeff=-

brand new 2.5"

http://www.ebay.com/itm/380606319348...84.m1423.l2649

http://www.ebay.com/itm/Stainless-St...item58a4d37c31

AH! Thanks very much for the links, =Jeff=!

Dom: As you know my situation was to find a replacement for the one NPP actuator I have with a perforated diaphragm. I found an actuator that might in fact work quite well, in the form of an exhaust heat riser gate valve. But, the gate itself is only about 1.5" in diameter and would be restrictive. So, one would require some bracket fabricating to fit the actuator to the bigger NPP gate.

If Jeff's source eliminates all the fussing to convert it, then I'm all for it! I'll have to check the ID of the NPPs I have, but I suspect the 2.5" valves Jeff located are the correct size (or close enough, especially on a dual outlet 17228 Dynamax muff!)

[WARP TEN]

Originally Posted by ZZZZZR1

Bob You have Corsa and electric cut outs too?? Ohhhhhhh. Details please!!!! Love these modifications! Cheers
David

Sorry to disappoint you Dave but I ditched the Corsas recently after 15 years on 2 different Zs. In my old age I am just tired of the constant noise and my wife thought they were too loud (she always said she could hear me coming about 3 blocks away!). I am back to my stock '95 system (Marc still had it at his shop from the swap last year) plus the QTP cutouts. As I noted in an earlier post, the Corsas are straight through on both pipes of the mufflers so cutouts wouldn't add anything there. The stock setup gives me relative quiet when I want it (slightly louder than pure stock as I have headers and no cats). The cutouts provide a full straight through system for the track or just for general intimidation and grins. I am currently running them cracked open just slightly for a little extra rumble. --Bob

[Pete]

Originally Posted by WARP TEN

Sorry to disappoint you Dave but I ditched the Corsas recently after 15 years on 2 different Zs. In my old age I am just tired of the constant noise and my wife thought they were too loud (she always said she could hear me coming about 3 blocks away!). I am back to my stock '95 system (Marc still had it at his shop from the swap last year) plus the QTP cutouts. As I noted in an earlier post, the Corsas are straight through on both pipes of the mufflers so cutouts wouldn't add anything there. The stock setup gives me relative quiet when I want it (slightly louder than pure stock as I have headers and no cats). The cutouts provide a full straight through system for the track or just for general intimidation and grins. I am currently running them cracked open just slightly for a little extra rumble. --Bob

Bob,as I remember Corsa has one tip open on the mufflers other is a dummy tip, this is why one tip is cleaner then the other.

Trying to push 7500RPM 550hp thru a single 2 1/2" pipe hmmm

Pete

[WARP TEN]

Originally Posted by Pete

Bob,as I remember Corsa has one tip open on the mufflers other is a dummy tip, this is why one tip is cleaner then the other.

Trying to push 7500RPM 550hp thru a single 2 1/2" pipe hmmm

Pete

You may be right about the Corsa mufflers although I thought both pipes flowed exhaust. I do know that the stock C4 Corvette mufflers are like that, however, as the rear two thirds of the stock muffler is a closed section called a helmholz resonator. That's why one pipe is essentially a dummy. The helmholz resonator has a pipe going into it but no exit, so just sound waves go in. Its purpose is to cancel out the sound waves for one of the two resonance frequencies of our engines (I think the one at 1,800 rpm while the center resonator handles the resonance at 3,400 rpm. Or the vice versa). It performs a similar function to that of Corsa's "Reflective Sound Cancellation" approach which has the resonators located around the outside of an otherwise straight through pipe. --Bob

[mike100]

Originally Posted by Paul Workman

OK, I got a clear picture now.

Your approach is interesting, and I suspect has very "digital" (read: either ON or OFF!) characteristic, compared to the direct vacuum line from the plenum to the NPPs (i.e, the FBI approach).

Believe me, I would have liked to have just run from plenum vacuum, (I tried it), but there is rarely a flat stretch of road where I live and the uphill sections raise the engine load and cause the manifold vacuum to drop down enough to let the flapper start to crack open. It doesn't have to open very far before the resonance starts in.

My way requires both a (programmable) minimum rpm and throttle position condition. Surprisingly, it isn't as 'digital' as I would like it since my vacuum hose diameter being restrictive, causes a pretty slow opening and closing. As time permits I will run a second line and fiddle with the vacuum switch setting. I might even tweak the secondary activation curve in the lower revs near the resonance point around 1800-2000 rpm.

It was a fun modification, especially since I have an aversion to all the extra attention loud pipes get you.