NPP exhaust valves on my SW 3" pipe set

[mike100]

The one thing I completely forgot about was that once the secondary is activated, it will stay on until less than 5% throttle position occurs. You have to let off the gas all the way briefly to get it to set back to quiet.

Another less complicated method might be to use the vacuum switch to just trigger on plenum pressures x amount of KPa near atmospheric or full throttle-high load. hmmm. thanks for the ideas...

[WARP TEN]

Originally Posted by mike100

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.

This is why I like the electric cutouts--you can adjust them whenever you want. I run them closed around town for a quiet stock sound, or cracked slightly open for some extra rumble. For the track--or just for grins--wide open. --Bob

[HAWAIIZR-1]

Sorry, I'm a bit late...........but FRIGGIN SWEET!! Thanks for sharing.

[Paul Workman]

Originally Posted by mike100

The one thing I completely forgot about was that once the secondary is activated, it will stay on until less than 5% throttle position occurs. You have to let off the gas all the way briefly to get it to set back to quiet.

Another less complicated method might be to use the vacuum switch to just trigger on plenum pressures x amount of KPa near atmospheric or full throttle-high load. hmmm. thanks for the ideas...

Intriguing situation...

Well, having thought about your circumstances a little - specifically the hill/mountain factor (almost foreign to us FBI and other flatlanders) - there are perhaps a couple solutions: Go to a manually controlled, electrically switched cutouts (as Bob suggested) or control the vacuum solenoid with a sensor sampling and triggering on the TPS voltage perhaps???

The manual approach is, well, manual! (But, NOT spontaneous by any stretch, which is the main purpose of NOT going that route.).

I like the TPS voltage approach because the "on or off" aspect depends on throttle position only, and the spontaneity, of course. The threshold could theoretically be adjusted to trigger at any desired amount - even on the fly, if that was desirable too (several interesting options - discussed further down).

To address your concerns for lag and latent "on" mode (until the throttle dips under 5%), it might be addressed in three parts:

1. locating your EGR type vacuum solenoid(s) at or near the NPP valves, and
2. install a vacuum ball reservoir also close by the NPPs
3. triggering electrically from actual throttle position instead of ECM secondary control.

Having the solenoid close to the NPPs localizes the access to atmosphere, and further reduction in vacuum bleed off in the NPPs could be cut in half again by twin EGR type solenoids; one for each NPP, if even necessary.

Vacuum closing the NPPs would come from the vacuum ball nearby when the vacuum solenoids* is/are switched "off".

*Keys to the system are 1) a sensor/switch that reacts to perhaps the specific TPS voltage without interfering with its intended purpose (such as perhaps a high input impedance op amp circuit set to trigger at a predetermined voltage close to the WOT value), and 2) the vacuum solenoid needs to isolate the vacuum side of the switch when "ON" so as not to bleed air into the vacuum ball reservoir when the NPPs are switched open.

In the end, hypothetically the system would spontaneously react very quickly ON and OFF, according to throttle demand. And too, the system could be turned off completely with a switch, so as to avoid nuisance activation, OR locked ON too, for that matter.

In the end, this could also quicken the response to the vacuum only (FBI) setup, IF desired...IF.

The current vacuum system would change (the sound) from a mmmmWAAAAAH and back to more of a mmmmBAAAAH and equally/nearly as quick back to "mmmm" sort of thing!

Food for thought...

[mike100]

Originally Posted by Paul Workman

...
To address your concerns for lag and latent "on" mode (until the throttle dips under 5%), it might be addressed in three parts:

1. locating your EGR type vacuum solenoid(s) at or near the NPP valves, and
2. install a vacuum ball reservoir also close by the NPPs
3. triggering electrically from actual throttle position instead of ECM secondary control.

I like those ideas. Next trip to the wrecking yard and I may come home with another GM vacuum ball and another EGR solenoid. A high impedance TPS monitor circuit should work, as would going low-tech with a micro-switch just like my old nitrous system used to employ. It isn't too bad on the secondary though, just more instant activation would probably be a good first adjustment.

[Paul Workman]

Originally Posted by mike100

I like those ideas. Next trip to the wrecking yard and I may come home with another GM vacuum ball and another EGR solenoid. A high impedance TPS monitor circuit should work, as would going low-tech with a micro-switch just like my old nitrous system used to employ. It isn't too bad on the secondary though, just more instant activation would probably be a good first adjustment.

I get the sense that you're getting very close to something good here, short of transplanting the entire NPP electronics and hardware to this app.

Bouncing this back and forth, for the sake of discussion, I completely glossed over you mentioning moving the vacuum switch to the plenum. That might work w/o designing a TPS voltage sensor/switch.

Now, the one thing that is NOT a problem with the electrical/manual cutouts or the relatively slower to react FBI system, i.e., the plenum activated NPPs, is rapid oscillation between ON and OFF or "chattering". This problem would depend largely on the sensitivity of the particular vacuum sensor/switch, primarily at the critical moment vacuum level crosses the trigger value. (I wouldn't want to unnecessarily "fix" a problem that never existed, but worth keeping in mind it could happen, and a fix could be applied if needed.)