meyerweb

This thread:

https://www.corvetteforum.com/forums...ck-result.html

and many others talk about the 1700 rpm hitch, when the NPP valves close, even in track mode, below 1700 rpm. Quoting from the post above

My car, built in late April of this year, doesn't seem to have this behavior. I've tested it in several ways. In all cases Engine Sound Management is set to Auto.

Cruising in 6th at speeds between 55 mph (about 1200 rpm) and 65 mph (about 1500 rpm). Mode switch set to Sport. Switch mode to track and the exhaust note gets significantly louder. Switch back to sport, and it gets noticeably quieter. Based on the linked post, I would not expect it to get louder when switching to track below 1700 rpm.

Cruising at about 65 in 5th (IIRC). In any case, engine rpm about 2000. Mode set to track. Gradually slow down until revs drop well below 1700. I don't notice any sudden change in tone or volume at any point.

Am I missing something in the way I'm doing the above tests? I've done them multiple times, and the behavior described is consistent. I can't get it to quiet down below 1700 rpm in track mode. Is it possible Chevy has heard the desires to have the valves stay open all the time in track mode, and made a running change in the software?


Something else that is different than I expected, but maybe everyone else already knows: I had assumed the valves were either open or closed. But it appears they operate at intermediate positions, too. Switching from Tour to Sport make the exhaust louder, and switching it to Track makes it louder still, while staying at the same speed and rpm. (I mostly notice this at slower speeds, where wind noise doesn't mask the exhaust note so much.) That seems to indicate that in Sport the valves were open only part way, while in track they were open further / fully.

Higgs Boson

they operate off more than just RPM. throttle position, i am sure also things like manifold pressure, vehicle speed, driver demanded power, etc just to name a few things.

this is why Theta created/is working on a manual switch to over ride the seemingly unpredictable NPP logic.

Elite275

I wired mine up via Theta's DIY and it was relatively simple and works like a charm. I have mine open 99% of the time, but it's nice to be able to shut them for coming home late at night. Prior to this, I had simply pulled the fuse and left open all the time. With Theta's method when the switch is off it is like pulling the fuse, when the switch is on it operates the way your current setup is working stock where the mode selector controls the behavior of the valves.

meyerweb

I understand Theta's mod, which is designed to let you keep the valves open, even under 1700 rpm. Based on the post I linked, the under 1700 rpm seems like a hard limit. I'm saying that mine stay open under 1700 rpm even without the mod.

Higgs Boson

in track mode they rarely close. open at idle as well.

c6switchblade

Just to confirm, I just got a set of NPP mufflers which are arriving tomorrow for my non npp car. If I do not hook up the rear actuators, they default to always open, correct?

xp800

Interesting observations. The hitch was more noticeable (to me) on light acceleration through the 1700RPM point rather than steady state cruise. Entirely possible things have changed. My current mid-December '15 A8 has hitch issues, but not like the M7 did.

Try this experiment...

1. Set ESM to Track so that the mode dial won't be a variable.
2. Gradually accelerate.
3. From 2-3 shift soon enough that the RPMs fall to maybe 1500.
4. As you tip in to accelerate through 1700RPM, pay close attention to the sound.
5. Try this for the 3-4, and 4-5 shifts where the shift point allows 1500RPM or less on the upshift and then tip in through 1700.

In this scenario, the change in volume at 1700 would be night and day when in ESM Off/Track if things are still programmed they way they had been.

For me, it was annoying since this RPM range of operation was 'normal' driving around town. Anything spirited it's a non-issue. But I have to say not nearly as annoying as the A8 and incessant AFM mode I'm dealing with now... But that's another matter.

I never explored all the other ESM modes (or left the ESM in Auto) when I had my M7. I, like many others, wanted ESM Off/Track to be be loud all the time and that was it. When that wasn't happening, it lead to the fuse pull and now the cool new MildToTheta switch.

If you can definitively confirm a programming change, I'd be happy to update the NPP thread. I have no access to a '15 M7 to test this on my own though.

meyerweb

Sorry, I missed your reply. I'll give what you suggest a try in the next couple of days, when I can get some highway time in.

meyerweb

So I tried doing this in 4th, 5th and 6th gears. I repeated this multiple times yesterday evening, and this morning and evening. (Too much traffic to run that fast in 7th.) But I got some interesting results.

In 5th and 6th, there is definitely no "step" between 1500 and 2000 rpm, either accelerating or decelerating gradually. In 4th, however, the step at 1700 rpm is very, very obvious.

What I'm not sure of, though, and will need to try to listen for, is whether in 5th and 6th the car is staying in quiet(er) mode even beyond 1700 rpm, or whether it's coming out of quiet(er) mode before 1500 rpm. I'll try some tests in 5th running lower than 1500 and above 2000 to see if I notice a step. I may have to wire in Theta's remote switch mod so I can manually switch the valves are between open and Track mode and see what happens with the sound. It'll be a while before I get around to that.