Then you need to take your car in as it is not functioning normally.

 

I've never noticed V4 vs V8 transitions. I had to watch the gauge cluster and look for the V4 which only came on for very short periods of time and I would have never even known about V4 until I read about V4 on this forum several weeks ago. I was in tour mode so exhaust was quiet and I was just cruising on the highway at around ~70mph.

 

Well, I guess we need to define normally. Car is dealer maintained, I have no reason to believe there's any issue with it not performing as designed. I just don't agree with the design when it comes to V4 mode and the lack of ability to turn it off in all modes..

 

C8 Corvette bogs in v4 mode until it eventually changes to V8

If any part of this statement is true, your car is not performing normally.

 

It bogs and it also has a 'chirp' noise. I have to constantly use the paddles to downshift or hit the throttle to keep it in V8. It's annoying. I mean they need to decouple engine settings from DCT settings. I love track mode but you can't have the DCT hold 2500 rpm all the time, it's wasteful.

 

Yes there's a bunch of cars that go in/out of V4 with no perceptible change. Then there's the unlucky owners that have a car that clunks and sometime jerks during the transition and then when in V4, the car drives like crap.

 

I would really appreciate it if you could

 

OK. The only reason brands from Fiat to Ferrari, VW to Rolls Royce, Mini to Mercedes, and the pinnacle of motor tech (F1) haven't switched to "cheap, simple, superior" voice coil technology is because they're short sighted. If you say so.

 

Agree. I don't notice anything remotely like "bogging" in my C8, no matter the mode.

 

Same reason why NASA and SpaceX don't still use vacuum tubes.

 

Frankly there is something wrong with your car OR the way you drive! From what you say you are doing to avoid V4 it appears to me it's THE WAY YOU DRIVE.

I often drive in Z-Mode Power set to Track. I have zero issue with the car shifting at too high an rpm. Because when in town, I use a light right foot! BUT I also use MY Mode and have zero stumble etc. I'm with the group that only knows it's in V4 by looking at The Dash Indicator. BUT I am not using a heavy right foot when in my Mode (set to Sport.) In fact, my guess is I get as good as gas mileage as you do when I'm in in Z-Mode not driving aggressively. My car is not downshifting. No need, with a light throttle it's very responsive. Of course, Z-Mode set with Power to Track it does not every go into V4.

You should watch this video and see why this fellow always drives in Z-Mode power set to Track. Note his car in may drive situations is not shifting at high rpm. Like you says he hates the downshifting when V4 allowed. As I said, how it drives, what rpm it shifts is very right foot dependent.

What is a bit silly is the 0.33:1 8th gear Over Drive Ratio. Also 7th, even 6th OD ratios. Did you know 4th gear is and overdrive ratio?? 5th at 0.67:1 OD is about the same as the 0.7:1 many slushbox box transmissions used in the past!

A Main Reason for the higher gears and crazy OD ratios for GM to get the best mpg driving at the max hp the EPA test requires (probably 75 to 80 hp) i.e. with very little throttle. It's only for getting good gas milage if on a flat interstate driving under ~65 mph. If you are using more throttle to mess with gear selection by having it downshift YOU ARE WASTING GAS! Try a light right foot in Z-Mode Power Set to Track.

You Tube

 

I HAVE to do something to get the car to downshift otherwise it wants to be in a high gear at 1250 rpm when steady cruising. At those low rpm, the engine makes a bog low drone and a chirping noise when there's slight load. What would you like me to do to not have that happen? I would like to have it solved. It seems that the other poster has same issue.

 

Bogging down is a subjective term - when I read it, I think of the hesitation that one feels in older, carburetor engines when the throttle piston pump is not adjusted properly. You press the pedal, get a brief hesitation, then the car takes off. I get nothing like that when mine transitions from v4 to v8. If it is in V4 at steady cruise, and I press very very lightly on the accelerator, I can sense very subtle low frequency rumble that is remotely reminiscent of engine lugging (but its very subtle - and I'm not saying it is lugging). I don't perceive that as bogging. But if I use any more throttle, it will instantly exit V4 without perceivable hesitation. The Service Manual says it takes 250 msec and two revolutions of the crankshaft (not sure those are consistent but that is what it says) to switch between modes.

 

If I only push the throttle slightly it will continue to low drone and chirp, only a more forceful application of throttle gets it out of that state. That's what I am saying.

 

I've never noticed it from a performance standpoint, but I have noticed it when in My Mode with Engine Sound (Exhaust) set to Track. I was turning a corner, and looked for another car along side me, because it sounded like a modded-out rice burner. Then I realized it was my car, looked down, and saw V4 on the dash...

I think a person is more likely to notice the exhaust sound than the performance...obviously much more so if the NPP valves are open. The only reason I'd have to disable AFM is purely for the sound. It'll more than likely only going to V4 when being driven very casually anyway.

 

Feel bad you are not feeling what I do about my C8 and even more my E-Ray after 62 yeas of EVERY DD being a standard shift, including 5 Vettes. Please watch that complete video. He shows why it's like a different car in Z-Mode Power set to Track. You can watch his miles of driving many in traffic and as I say with a light right foot you will find it does not shift at high rpm (or perhaps after some miles learns not to.)

SIDEBAR
Now if I told my wife the way she takes off is not right, she would be mad so I don't! But although she doesn't drive fast, she takes off very quickly. Don't know why. But her foot quickly comes off the gas pedal and her BMW X5 SUV instantly up shifts. The C8 will not. Start with a heavy foot and Z-Mode thinks you are racing! BTW my wife has never driven any of my 7 Vettes!

I'm going to chuckle when she takes off in her new car we have on order. But convinced her this next should be a PHEV! Not that much more money. BMW uses a pancake electric motor bolted to the flywheel. The rest of the drive train is essentially the same AWD as her prior 3. (Her current 2021 goes, like the last, to daughter in OH.)

The specs are interesting. The 2025 I6 Twin Turbo has more power than her 2021, 375 vs 335. The electric motor is 108 hp for a total of 483. But as with my E-Ray instant max electric torque at 0 rpm. Now it is heavier due to the EV motor and battery, but they quote 0 to 60 in 4.6 seconds. It will travel about 50 miles on only electric, so it has a big battery. Don't have the secs of weight but car weight is much higher than the Non-Hybrid version. It comes with a charger that takes 21 hours to bring a depleted battery to max capacity. On a 120 line. I had a 240 volt line put in the garage when we had the house built 28 years ago. In case I wanted to get a 240 volt MIG welder. I have a smaller one that is 120-volt input so have never used the 240 outlet. We'll see how much we use it. Really never have to plug it in. Can operate like my E-Ray and let it charge the battery when braking and use the extra power for performance. We'll see

More than myself, she is very excited about the $3.5 billion EV battery plant being built not far our airport ~10 miles away. The steel framework for what look like a 4 story building is up (may be just high ceailin? It is owned my a Janasese Compny with ties to a Chinese company. The city is building a massive traiing center near the plant sight. They will be supplying batteries for Hybrids and EV's to BMW in the Western part of the state. hey have 11,000 folks building SUV's for the World at that complex.

 

As you may know, regardless of the engine sound setting, when the car goes into V4 mode it closes all the valves. If you have NPP both the cylinder deactivation exhaust flow control valves and the tailpipe exhaust flow control valves all close in V4. If you do not have NPP, then just the cylinder deactivation exhaust flow control valves close. But, yes, I can hear a change in exhaust tone when it goes into V4 mode.

The following is from the Service Manual:

Exhaust Tail Pipe Flow Control System Description and Operation

Engine Exhaust Flow Valve System
The engine exhaust flow control valve system has two subsystems:
1. The exhaust tail pipe flow control valve system. Also known as the exhaust sound quality valve control system.
2. The cylinder deactivation exhaust flow control valve system. Also known as the active fuel management (AFM) exhaust flow valve control
system.

Exhaust Tailpipe Flow Control Valve System
The exhaust tailpipe flow control system is used to tune the exhaust note for high performance vehicles. The vehicle is equipped with two tailpipe
exhaust valves. One in the left tailpipe and one in the right tailpipe. Each exhaust tailpipe valve is installed in the low restriction exhaust path of a
dual outlet muffler, near the exhaust tip.
When a tailpipe exhaust valve is open, the low restriction exhaust path is opened to the atmosphere, and the exhaust note becomes more
aggressive.
An output circuit from the chassis control module is used to control the actuator that opens the left and right exhaust tailpipe valves. The exhaust
flow control valve opens and closes when the chassis control module commands the actuator by pulse width modulation of the control signal.
To provide a more aggressive exhaust note when the vehicle is started, the exhaust tailpipe valves are opened during an engine crank event during
specific modes of operation if that option is available. Once the engine is running, accelerator pedal position, transmission gear and engine speed
are used to determine the commanded state (open or closed) of the exhaust tailpipe valves.
There are four specific exhaust performance modes that result in different behavior of the exhaust tailpipe valves. These modes are:
Note:
You may notice an exhaust tone change due to the AFM system activation, or during certain driving conditions to meet Federal noise pass-by
regulations. Review the cylinder deactivation exhaust flow control system operational modes listed below for additional details.

1. Winter/Eco Mode: Exhaust tailpipe valves will be closed at all times when the engine is running.
2. Tour Mode: Exhaust tailpipe valves are closed when the engine is idling and during normal/non-aggressive driving. Valves open during
aggressive driving.
3. Sport Mode: Exhaust tailpipe valves are open when the engine is idling and during most driving scenarios. See note above.
4. Track Mode: Exhaust tailpipe valves are open at all times. See note above.
It is possible to personalize the exhaust sound. When engine sound enhancement is turned off via the personalization menu, the exhaust tailpipe
valves will be put into track mode no matter which vehicle mode (Winter/Eco, Tour, Sport, or Track) is displayed on the drivers instrument panel.

Cylinder Deactivation Exhaust Flow Control Valve System

As a means to improve fuel economy, the engine management systems in some vehicle applications include provisions to deactivate half of the
engine cylinders under certain operating conditions. For example, under a light load. The cylinder deactivation exhaust flow control valve
subsystem is used to mitigate the impact that powertrain engine cylinder deactivation (active fuel management) has on the quality of the exhaust
sound. When the active fuel management system is in operation, the cylinder deactivation exhaust flow control valve subsystem takes over control
of the exhaust tailpipe flow control system. When active fuel management is operating, the exhaust tailpipe flow control valves are commanded shut
resulting in a quieter exhaust note until the active fuel management system deactivates with increased throttle demand at which time the exhaust
tailpipe flow control returns to the operational status determined by the vehicle specific mode that is being used.
The cylinder deactivation exhaust flow control system controls the undesirable exhaust noise generated during the cylinder deactivation process.
This is achieved through the use of up to two electronically actuated cylinder deactivation exhaust flow control valves in the vehicle exhaust system.
The cylinder deactivation exhaust flow control valves are commanded to the closed position by a pulse width modulated signal from the chassis
control module in response to active or pending engine cylinder deactivation. When the cylinder deactivation exhaust flow control valves are in the
closed position, the engine exhaust flows through a hole machined in the plates integral to the valves. When the engine is operating on all cylinders,
the cylinder deactivation exhaust flow control valves are commanded to the open position in order to minimize exhaust restriction. To provide some
control hysteresis, once the cylinder deactivation exhaust flow control valves have been commanded to the closed position, they are not reopened
until the engine torque reaches a calibrated minimum value that is determined as a function of the driver selectable performance mode.

 

And it does that because you don't want to hear it in V4 mode. It would probably sound like it's missing on 4 cylinders, because it is. My first reaction to my base exhaust was how quiet it was. I kind of liked it. Doesn't mean I might not want to change that. But understanding everything going on with the engine and AFM and the exhaust is critical. I want a tune to eliminate AFM and add some mild performance tweaks, and a dual center exit exhaust with no valves. For a non-NPP I'd think that would just need some AFM valve simulators plugged into to the harness.

 

Ha. And GM's euphemistic version of that is "to mitigate the impact that powertrain engine cylinder deactivation (active fuel management) has on the quality of the exhaust sound. "

They also claim to have active noise cancellation but no-one has ever reported being able to tell if it works or does anything other than issues it created when an aftermarket speaker was added. Its mentioned in the Owner's Manual and described in the 2020 Service Manual. And its on the Bose website here:

https://automotive.bose.com/vehicles...ette-stingray#

although its called Engine Harmonic Cancellation there. Tadge described it verbally a while back, and he said its purpose was to cancel the undesirable sound created by V4 mode, but I have never seen that specific explanation in any GM or Bose material.

 

Interesting. I did not know that - wonder if there's something wrong with mine - happened twice yesterday and I literally looked for another car out the driver side window only to find myself alone....

I'll see if I can get it to happen again. I believe I was in My Mode. I also had the PDR running - wonder if I'd be able to hear it from the recording, and if the overlay shows the driving mode...