NPP Exhaust Control Valves help control resonance without the weight and backpressure of a resonator. However the use of engine vacuum can also cause the valves to open during low vacuum or high MAP conditions. Typically, this happens on inclines causing the valves to crack open increasing resonance. I recently had the opportunity to find an NPP Retrofit kit by Nakid Parts. However, in trying to install it, it didn't work well or not at all. Everything checked out and it did work when using a brake bleeder as a vacuum source. When applying engine vacuum however the exhaust control valves remained in whatever position they were in with engine start. Everything checked out. NakidParts checked the unit and found it to operate properly. They stated that they had 800 units in operation including one for Jay Leno. Maybe it's an issue w the LT-5 v an LS-3 or LS-7.
Reviewing the electrical, pneumatic circuits there was no reason why it shouldn't work. But it just didn't.as Sherlock Holmes would say to Watson,
'How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?'
It's now clear the solenoid used w the NPP in a Box Retrofit kit has an issue, at least, w LT-5 engine vacuum. mike100 has done his own NPP control using a GM EGR solenoid. I decided to try this solenoid in place of the one used for NIAB retrofit.
So here's a video showing the operation of the NPP retrofit BUT using a GM EGR SOLENOID in place of the stock NIAB solenoid.
