Does NPP in sport mode give better gas mileage than a non NPP equipped car? In general does NPP affect gas mileage at all?

 

I haven't seen anything on this, I would be surprised if it did. I have NPP, but I drive in myMode with the exhaust set at "track". I've never driven the car without it being in track setting so I don't know if it would be any different. Even in track mode the NPP is pretty quiet.

 

My guess is NPP cars on average would show lower mpg, but that it would more a function of driving style. Those ordering NPP are probably more likely to operate at a higher average rpm, to enjoy the exhaust note that prompted them to order it in the first place.

At lower rpms, the 2 NPP valves are more likely to be closed, depending upon setting, in normal street driving.

 

Your wanting a Corvette cause of gas mileage? I mean going down the highway in 4 cylinder I have seen some high numbers. Most people that are concerned about gas mileage are thinking of an economical car. My last Corvette I averaged 18. I believe it will be similar with the C8. To tell you the truth I doubt NPP alone will do much for mileage either way.

 

I got it so that I wouldn't upset the neighbors in the morning.. that is, i keep it in quiet mode around the neighborhood. BUT I wanted FULL POWER.. all 495 horses, not 490.
Since it's on and off, hard to say about mileage.

 

This was driving back to Colorado Springs from the dealer just before 500 miles. Best 50 mile average was 34.9 mpg. Around town with no highway 18 mpg. At 85 mph on interstate I get 29 mpg. I find the computer is a little high by around 1- 1.5 mpg. Going 2 miles to the club 12 mpg. By the way I only set the cruise control to video the tachometer red line change at 500 miles.

 

Is the NPP option working out good for you? I leave the house before 6 a.m. most mornings and, like you, I don't want to make too much noise then. I'm not concerned about the extra 5 h.p. though. I'm still on the fence about ordering the NPP on my car, so I'd appreciate any info. you can provide about it as to the ability to control some of the engine exhaust noise. I thought I read previously that the engine starts up with the exhaust fully open which would make more noise. In which case the NPP option wouldn't do anything to decrease that noise. Sorry, but I'm confused???

 

Based on C7 and what I’ve read here on CF about C8, you are correct - the exhaust will always be open at cold start regardless of setting. My neighbors got used to it, I assume, I tried to be courteous by switching NPP close the exhaust quickly.

 

Nope! NPP valves are closed (even if set in Track Mode as I have mine) when you're looking to consider mpg. In fact drive the car like some Grandpas (BTW I have two Great Grandsons and NEVER drive that way) and the valves will always be closed. Drive at larger throttle openings (as I often do in Z Mode Powertrain set to Track) and the valves are often opened and my mpg goes low! When I drive in MY Mode I have set to Sport it goes in all gears and if just cruising will go into V4 Mode and 8th gear - NPP valves closed at that point. ( BTW in Z Mode Power set to Track it will seldom shift past 5th and won't every go in V4!)

Bottom Line: if trying to measure mpg you'll be in a mode where NPP valves will not be open! Question answered.

 

If you get NPP regardless of what Mode you drive, on start-up:

1. The NPP valves are open
2. Engines rev's higher for ~30 seconds
3. Mixture is richer
4. All above to warm up the CATs.
5. Note some of us wish it could stay that loud- but doesn't

If car is in the garage start up with the doors closed!

 

As someone above pointed out, it starts open, but .. As I drive away with the car slightly warmed up, it's closed. I don't then bother the neighborhood. Coming home, same deal. With it in quiet mode I can putter on in and up my driveway without disturbing anyone.

Hard to tell if I'm actually getting more power. How would I know, never having driven one without it. Seat of the pants probably woudn't show it.

 

So is there a way to open and close the NPP valves manually? Or does NPP operate only under the above conditions?

I too am confused about it's operation and the reason to purchase this option in the first place.

 

^^^
No, can't open manually or electronically as was possible in the C7. NPP was designed and built by Tenneco who supplies the whole exhaust system (they did for the C6 and C7 as well.) It operates with stepping motors. There is feedback to the C8 system. They are either fully open of fully closed. In the C7 you could pull the fuse to the electric motors and it would not trip a CEL. With the 4V valves that operate fully open or "partially closed" in V4 Mode a CEL will drip if disconnected.

When the NPP valves open is dependent on drive mode. In the C7 with my M7 it was easy to define about when.
In Track the opened at ~1700 rpm
In Touring at about ~2500 rpm
In Sport somewhere in-between

In the C8 it "may be" about the same. It says there is a Stealth Mode when set in Weather. Not sure they will never open BUT as I said, on start-up they will be open for 20 or 30 seconds to heat up the CATs quickly to reduce exhaust pollution.

It's cheap compared to what I consider a better sound, Borla. Just checked they have several sound levels but cost ~$4500!

No one can tell you to order or not, it's up to what you want. I have had NPP in my C6, 2014 Z51 and 2017 Grand Sport. It's OK, easy to order and relatively cheap. Does it sound like the Borla's I have on my street rod- no! Not even as good as the Flowmasters I installed on my 1988 Vette or S-10 truck. But easy to order and relatively cheap. PS: You'll never "feel" the extra 5 hp! No one buys for the hp increase! Frankly with the low noise C8 Coupe, not nearly as loud as on my C7s. Worth $1100, is to me.

 

Thanks Jerry, I am just trying to understand how they operate, at first I thought there was an on off switch which I probably would prefer. I hear some say it's not loud enough but I'm not looking for Borla type sound, just a little extra that reminds me what I am driving! I'll keep them on my build.
Dan

 

I do not want to disturb the neighbors too, so when I leave early I start the car with the door down. The NPP is open at startup..After a few minutes it quiets down..Then I head out...

 

Once you've started the engine you could put the car in Weather mode which invokes the NPP Stealth mode (closes the NPP valves).