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If anyone has an aftermarket exhaust you know V4 sounds like ****. I like driving in manual mode sometimes but not all the time. I also don't like putting my car into track mode all the time. I just don't want the AFM system to be active. I personally think AFM systems are a joke and the MPG gains are so minimal the benefit isn't enough for me to not want to delete mine. I see a Range Technology disabler in my future. Who is running one and what have your results been? I've heard they work great.
This is why aftermarket exhausts that retain the AFM valves are important.
The only way to disable AFM in the C8 is to unlock the ECU and disable it in the tune ($$$).
I’m not aware of any issues with AFM and most times don’t know if it’s active or not but driving yesterday it sounded like it got confused activating and deactivating and made a weird sound as the light kept flickering.
There are several things I wish were owner controlled. The car has a lot of choices in terms of adjustability. but there isn’t a switch for AFM on/off. Same with the 4GLTE connection and Onstar data transmission. Why can’t the owner configure all of these “features” as active or not?
I would gladly forgo any gas savings if I could deactivate AFM….. And I would feel much better about owning a gm vehicle and gm in general if I could turn off the cars connection 4G connection.
Last edited by 24RiptideBlue; Jun 7, 2024 at 06:13 PM.
I’m not aware of any issues with AFM and most times don’t know if it’s active or not but driving yesterday it sounded like it got confused activating and deactivating and made a weird sound as the light kept flickering.
There are several things I wish were owner controlled. The car has a lot of choices in terms of adjustability. but there isn’t a switch for AFM on/off. Same with the 4GLTE connection and Onstar data transmission. Why can’t the owner configure all of these “features” as active or not?
I would gladly forgo any gas savings if I could deactivate AFM….. And I would feel much better about owning a gm vehicle and gm in general if I could turn off the cars connection 4G connection.
Tadge actually spoke about the reason for the way it works. Some may dismiss it as either engineer speak, or corporate speak. And to some extent it might be, but I think it is mostly true. Basically, to meet overall CAFE standards they make certain compromises. And apparently, despite what some think, the Corvette does contribute to the fleet average mpg in a non significant way. And AFM is one way that Corvette contributes to the (what seem slight) reduction in fleet mileage. He said that if certain features that the EPA allowed as reducing fuel mileage can be disabled easily or are being disabled by owners, then they must evaluate the mileage without consideration of the feature. So it goes to why it can only be disabled in certain ways. Here is that text (obviously it is prior to the C8 because he speaks of the mix of manual and automatic transmissions, but it is still relevant):Tadge answered: I am going to start by assuming this question pertains to automatic transmissions only since AFM is turned off in all modes except Eco on the manual. I also assume folks know that when the auto is operated as a manual (i.e. "M" mode on the shifter), AFM is not operational.
As with many things in automotive design, we are not free to simply engineer cars to what each customer might want. We have many other constraints. Government regulations play a huge role in how we execute vehicles. Automobiles are the most heavily regulated consumer product in the world with every major economy in the world governing their design and sale in various ways.
Although it may seem like a simple matter to have a " turn off switch" to allow customers to choose between maximum efficiency and full time V8 operation, it is not. We use AFM (Active Fuel Management, or 4 cylinder mode) to enhance fuel economy under light load conditions. It only takes 12 - 40 HP (depending on model and speed) to push a Corvette down a flat road at highway speeds. Producing that small amount of horsepower with all 8 cylinders firing and then practically closing the throttle is not as efficient as running on 4 cylinders with the throttle blade more open. There are very measureable real world economy benefits in addition to fuel economy label, federal fuel economy standards (CAFE) , and gas guzzler tax benefits. The EPA sets the fuel economy and greenhouse gas emissions test procedures for our cars. They are very sensitive to possible customer "work-arounds" that would let customers quickly and easily by-pass efficiency mechanisms. There are even special test protocols that keep manufacturers from claiming a fuel efficiency performance that few customers will actually see. The way this is done is to require testing in a variety of the vehicle modes that customers are likely to use. If there is any question, manufacturers are required to actually survey customers to find out which modes they are using. Test procedures have also gotten more conservative to lower label values in response to customer complaints that they can't achieve the fuel economy printed on the label. This has not been an issue on Corvette, but we have to follow the new procedures along with all other manufacturers. That is why you have seen fuel economy label reductions even though the car hasn't changed.
OK, so if customers demanded it, could we put in an "AFM off" switch, and just let the label values and gas guzzler taxes fall where they may? We could, but that is where CAFE (Corporate Average Fuel Economy) becomes an important consideration. General Motors must achieve fleet average fuel economy targets or face stiff financial penalties from the government. It is true that Corvette volumes are but a small part of GM's total fleet, but every tenth of a mile per gallon matters when trying to balance the entire fleet. Further complicating Corvette's contribution to GM's fleet average is the fact that fuel economy regulations are a function of a vehicle's size. The fuel economy target is set based on wheelbase multiplied by track width (if they are different front to rear, you use the average). In the eyes of the government, Corvette is a very small car. It has a compact wheelbase and even though it is fairly wide, the track width is narrow because it has wide tires and track is measured at the tire centerline.
I hear from many customers that they are happily surprised with Corvette's fuel economy, especially on long trips. The Corvette is often the most fuel efficient vehicle they own. So even though the Corvette gets outstanding fuel economy given its performance potential, that doesn't help us on corporate CAFE. As far as the regulation is concerned, based on the vehicle's size, the target fuel economy is about 40 mpg - and that is combined, meaning average city and highway. Because of this, Corvette does have an important effect on our fleet average. We have to do everything in our power to minimize the penalty. That is why we use AFM everywhere we reasonably can on the automatic transmission which is about 80% of Corvette sales.
Of course these trade-offs are nothing new. We have used skip-shift on manuals for decades despite some customer's preference against it. Most of our competitors now have start/stop. Start/stop is not so bad in a traditional car with a quiet idle, but for cars where the engine has a lot of character, it can be very disconcerting to have the engine stop every time you come to rest. Customers have expressed extreme distaste for that feature on a Corvette and so far we have avoided needing to implement it. So, like many of the questions I'm asked, it comes down to how we must balance tradeoffs. We know what customers want and do the best we can to minimize any negative implications arising from government requirements.
I’m not aware of any issues with AFM and most times don’t know if it’s active or not but driving yesterday it sounded like it got confused activating and deactivating and made a weird sound as the light kept flickering.
There are several things I wish were owner controlled. The car has a lot of choices in terms of adjustability. but there isn’t a switch for AFM on/off. Same with the 4GLTE connection and Onstar data transmission. Why can’t the owner configure all of these “features” as active or not?
I would gladly forgo any gas savings if I could deactivate AFM….. And I would feel much better about owning a gm vehicle and gm in general if I could turn off the cars connection 4G connection.
The folks pushing high mpg don't care what you want for gas milage. Or that you pay a high price for gas! Their goal is reduced CO2 emissions!
Tadge had a good post re devices to defeat things like V4. The EPA has strict rules re devices that reduce mpg numbers. He said IF they felt enough folks were defeating what the manufacturer had installed, they can make the manufacturer perform a statistically sound survey. IF the percentage using changes their MPG published numbers they can make them change it or block the defeat device from working.
You may not recall but with 70% of us in 2020 buying the Z51 and 60% later that caused GM to have to reduce the published mpg number on the C8!
Don't think many understand the EPA plan to have the average car achieve 54 mpg in 2025 that was killed by a Pen in January 2017 was reinstated. Was reinstated quietly with a Pen in in April 2022. The new plan (with no/few details) is "on average" all cars will get 49 mph in EPA test in 2026. IMO we won't see details until January 2025. The initial effort and plan was to cut CO2 emissions in half. The new plan is aimed at the same. May not like it BUT may have to live with it!
I am aware all of these choices have everything to
do with government regulations and how they write the rules to even interpret the regulations and I just disagree with the EPA.
The “rule” that if the consumer can turn off the “feature” the EPA won’t let the manufacturer claim the savings is relatively new going back to the auto stop feature that changed from on or off driver selectable to activate as “on” every time the car is started forcing me to turn it off every time I drive my wife’s car.
30 or 40 years ago the EPA made a valuable difference but there are so many rules and regulations now I don’t know how any manufacturing business gets off the ground in this country and suspect is the reason many don’t and start any business involving manufacturing by finding an off shore company to collaborate with.
Now the EPA is trying to regulate internal combustion engines out of the market because congress won’t pass legislation because half the country wants to continue to be able choose what kind of car works for them. The EPA has decided they know better… that’s the EPA in 2024…
Way back in post 27, I mentioned and posted a link to a technical paper that discusses various techniques for fuel savings, called "Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles (2015)" that can be downloaded for free at this link:
and within that section is a discussion of Cylinder Deactivation. It has a short explanation for that, which strikingly sounds very much like Tadge's explanation including the statement that the deactivated cylinders act like springs. The explanation in the paper goes a little further to explain why the losses on those deactivated cylinders are nil. Here are some excerpts from that explanation:
"Cylinder deactivation, which shuts off multiple cylinders and results in higher loads on the remaining operating cylinders, can be utilized during part load operation to reduce pumping losses and friction losses. Pumping losses are reduced due to the higher loads of the operating cylinders, which require less throttling. Friction losses are reduced due to the lower piston loads of the deactivated cylinders, which have near-zero mean cylinder pressures. .....In order to deactivate a cylinder, the intake and exhaust valves are held closed. This creates an “air spring” in the combustion chamber, in which the preceding cycle’s exhaust gases are trapped and compressed in the upstroke and expanded in the downstroke. This compression and expansion result in reduced engine friction losses for the deactivated cylinders. In cylinder deactivation systems, the engine management system stops fuel from being delivered to the deactivated cylinders. Ignition and cam timing, as well as throttle position, are adjusted to ensure that switching from full cylinder operation to cylinder deactivation is nearly imperceptible. Until recently, cylinder deactivation primarily has been employed in engines with high displacement, which have low efficiency at light loads......."
I doubt anyone wants to wade through the whole paper - I didn't - but just a review gives some insight into the depths to which engineers go to find every last little bit of efficiency. The paper discusses a myriad of techniques - engine oils and friction reduction, thermal management, variable valve timing, turbocharging, and on and on. I find it a bit humbling. Remember the days of smog pumps and other crude emission reduction techniques that were not based on improved efficiency - that resulting in ever larger displacement engines that were less and less powerful - and they continued to run after being turned off? Finally engines are getting (relatively) smaller, more efficient, and yet remarkably more powerful.
Way back in post 27, I mentioned and posted a link to a technical paper that discusses various techniques for fuel savings, called "Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles (2015)" that can be downloaded for free at this link:
and within that section is a discussion of Cylinder Deactivation. It has a short explanation for that, which strikingly sounds very much like Tadge's explanation including the statement that the deactivated cylinders act like springs. The explanation in the paper goes a little further to explain why the losses on those deactivated cylinders are nil. Here are some excerpts from that explanation:
"Cylinder deactivation, which shuts off multiple cylinders and results in higher loads on the remaining operating cylinders, can be utilized during part load operation to reduce pumping losses and friction losses. Pumping losses are reduced due to the higher loads of the operating cylinders, which require less throttling. Friction losses are reduced due to the lower piston loads of the deactivated cylinders, which have near-zero mean cylinder pressures. .....In order to deactivate a cylinder, the intake and exhaust valves are held closed. This creates an “air spring” in the combustion chamber, in which the preceding cycle’s exhaust gases are trapped and compressed in the upstroke and expanded in the downstroke. This compression and expansion result in reduced engine friction losses for the deactivated cylinders. In cylinder deactivation systems, the engine management system stops fuel from being delivered to the deactivated cylinders. Ignition and cam timing, as well as throttle position, are adjusted to ensure that switching from full cylinder operation to cylinder deactivation is nearly imperceptible. Until recently, cylinder deactivation primarily has been employed in engines with high displacement, which have low efficiency at light loads......."
I doubt anyone wants to wade through the whole paper - I didn't - but just a review gives some insight into the depths to which engineers go to find every last little bit of efficiency. The paper discusses a myriad of techniques - engine oils and friction reduction, thermal management, variable valve timing, turbocharging, and on and on. I find it a bit humbling. Remember the days of smog pumps and other crude emission reduction techniques that were not based on improved efficiency - that resulting in ever larger displacement engines that were less and less powerful - and they continued to run after being turned off? Finally engines are getting (relatively) smaller, more efficient, and yet remarkably more powerful.
Yep, what find somewhat ironic is the original EPA Plan to Start January 2017, and one most auto manufactures agreed to accept would have resulted in the "Average Car & Pick-Up" achieving 54.4 mpg. That is from and EPA Press release that was based on a 1174-page technical document that defined by "Car Family" what would be required. Two seat Sports Cars and Pick-ups would be required to get ~49 mpg in EPA Tests.
Tesla was a vocal contributor and most agreed to get the average would require mostly Hyriids and some EV's. That was 2012 and EV's were not that common. I read the 2012 r1174 page repot and it outlined what companies would probably do. It was all being done to cut CO2 emissions in about half.
Then in January 2017 that plan was killed with a Pen. CA sued the government and said they were going to enforce it anyway. They lost but held on to their current plan, which 10+ states have joined "no new ICE vehicles to be sold after 2035." What is funny to me as we would be on a reasonable technical path to cut CO2 emissions in half when the powers to be said not that old plan good enough, we must eliminate all fossil fuels for cars, trucks and even not allow Natural Gas. An extreme unrealistic position. BUT follow the money, lots of folks making money! Technology be dammed, those benefiting don't care!
BTW it was not to be reinforced with gas guzzler tax! No way would "Rich Corvette, etc" owners be able to just pay money and destroy the world. The 1174-page Doc defined it was a very high tax of the manufacturer by "Car Family" if they did not meet their car family goals. Might as well not sell the 40,000 Corvettes BUT GM makes 750,000 very profitable Silverado's and Sierra's. It was NOT coincidence that GM made (makes) EV Silverado's in many types.
Yep Ferrari could still exist BUT their cars would have to meet the sports car family dictated mpg. Wonder why they stopped suppling all standard shifts in ~2012? And why they started to make "Performance Hybrids" that could converted to high mpg with Pirus type software and different battery types. And NO don't have to be plug-in, which is NOT needed to achieve high mpg.
Doubt many will read but lots of documentation in the attached Doc I started in 2019 including Porsche statements of what they planned for their sports cars! And BTW The Porsche Sports Car Family doesn't include SUV's or sedans. It's defined by type NOT name. Can't call a Volt a Corvette and use the average. Been updated many times and has the lasted EPA Plan of 49 mpg required in 2026: http://netwelding.com/C8_FWD_Hybrid.pdf
For those asking "why would you want to disable it", I'm looking at "affordable" catbacks that delete the AFM valves and make the car loud and apparently it sounds like crap when AFM kicks in. I don't have $4600 for a Borla system so gonna have to be in manual mode on the highway if I don't like the sound I guess.
Interesting. I don't think I've read any complaints of how somebody's full open exhaust sounded terrible in V4 mode here, but I experienced this on my '14 Silverado going from a stock exhaust to a dual Magnaflow. I would expect the same on an opened up Stingray exhaust with no AFM valves. I haven't kept up, but as others have said, no Range device available for it, and turning it off via a tune is indeed, very pricey last I checked. Trust me, I'd love to turn it off. Then I might consider a more open aftermarket exhaust.
There are several things I wish were owner controlled. The car has a lot of choices in terms of adjustability. but there isn’t a switch for AFM on/off. Same with the 4GLTE connection and Onstar data transmission. Why can’t the owner configure all of these “features” as active or not?
I would gladly forgo any gas savings if I could deactivate AFM….. And I would feel much better about owning a gm vehicle and gm in general if I could turn off the cars connection 4G connection.
If afm were user configurable, GM would have to do the emissions and mpg tests with it disabled, eliminating any benefit to the CAFE fuel mileage requirements. In other words, AFM isn't about saving YOU money, it's about saving GM money.
If afm were user configurable, GM would have to do the emissions and mpg tests with it disabled, eliminating any benefit to the CAFE fuel mileage requirements. In other words, AFM isn't about saving YOU money, it's about saving GM money.
My argument would be, it is configurable. All i need to do is put it manual mode, right? All I want to do is turn off AFM, not looking to run in manual mode too.
My argument would be, it is configurable. All i need to do is put it manual mode, right? All I want to do is turn off AFM, not looking to run in manual mode too.
If you don't want to drive in Manual Mode then drive in Z-Mode setting Power to Track. I drive there often as I did my 2020 C8 for 4 years. Since I had and now have MRC can set ride wherever you like. Tour if desired.
It will never go in V4, can't! If like some you don't like driving in 0.67:1 Over Drive in 5th or 0.5:1 Overdrive in 6th then use the Manual paddle and drive in the crazy 8th gear with 0.33:1 OD ratio. It's really for GM to get best mpg in EPA Drive tests. Doubt anyone drives a Vette like that (~75 max hp!) I don't use limited access highways so don't need 7th or 8th gear. If you do than pulling the paddle will make you feel better using those gears. Won't help your mpg very much!
My argument would be, it is configurable. All i need to do is put it manual mode, right? All I want to do is turn off AFM, not looking to run in manual mode too.
And that's exactly why GM can get away with disabling it in manual mode. Few drivers use that mode on a regular basis, so it doesn't have a significant impact on mpg. If you could disable it easily, without impacting other things, then many owners would, and the EPA would force GM to test the car with it disabled. Go back and read all of Tadge's quoted comments for a more detailed version of what I said.
What you want doesn't impact the EPA rules at all.
If afm were user configurable, GM would have to do the emissions and mpg tests with it disabled, eliminating any benefit to the CAFE fuel mileage requirements. In other words, AFM isn't about saving YOU money, it's about saving GM money.
I'd argue it's more about compliance than money... though if the consequence is fines, it's kind of the same thing. It's like how EVs and hybrids offset the fleet-wide MPG of a manufacturer's offerings so GM can get away with the Camaro ZL1 among all the other V8s and poor MPG vehicles, whereas Dodge for many years didn't have anything fuel efficient at all and didn't care and the EPA wrecked them with the ever-tree-hugging crackdowns on our V8s. Supposedly manufacturers have to meet these fleet-wide MPG requirements or bad things happen. Plus come on, any cost GM would incur would be passed onto us the consumer anyway, so it's more about protecting their profits rather than saving money... you could argue it's the same thing but I prefer my more pessimistic take on what you established. =)
I'd argue it's more about compliance than money... though if the consequence is fines, it's kind of the same thing. It's like how EVs and hybrids offset the fleet-wide MPG of a manufacturer's offerings so GM can get away with the Camaro ZL1 among all the other V8s and poor MPG vehicles, whereas Dodge for many years didn't have anything fuel efficient at all and didn't care and the EPA wrecked them with the ever-tree-hugging crackdowns on our V8s. Supposedly manufacturers have to meet these fleet-wide MPG requirements or bad things happen. Plus come on, any cost GM would incur would be passed onto us the consumer anyway, so it's more about protecting their profits rather than saving money... you could argue it's the same thing but I prefer my more pessimistic take on what you established. =)
Well the 2012 EPA Plan had lots of detail. For example, IF the Corvette Family (and other 2 seat sports cars) did not meet the ~39 mpg in EPA test than it would have been a very high fine for GM. Same for the other car families. BTW the Silverado had to meet about the same goal. Now for the 750,000 Silverado (and badged Sierra's) they could not afford the fine and would do all possible. (Frankly why IMO there are EV Silverado that get 650 hp, another 450 mile range and another that cost $72,000.) Oh you'd pay IF you wanted a ICE V8, but on average they would meet the goal. But for the Corvette might be cheaper for 40,000/year to just drop it! That is why IMO we'll see a C9 EV Corvette when the April 2022 details are released. They will meet with a blead of ICE C8's and EV C9! The percentage needed to meet goals would be done with price!
Well the 2012 EPA Plan had lots of detail. For example, IF the Corvette Family (and other 2 seat sports cars) did not meet the ~39 mpg in EPA test than it would have been a very high fine for GM. Same for the other car families. BTW the Silverado had to meet about the same goal. Now for the 750,000 Silverado (and badged Sierra's) they could not afford the fine and would do all possible. (Frankly why IMO there are EV Silverado that get 650 hp, another 450 mile range and another that cost $72,000.) Oh you'd pay IF you wanted a ICE V8, but on average they would meet the goal. But for the Corvette might be cheaper for 40,000/year to just drop it! That is why IMO we'll see a C9 EV Corvette when the April 2022 details are released. They will meet with a blead of ICE C8's and EV C9! The percentage needed to meet goals would be done with price!
What? 🤔…. I got maybe a third of that…. 🤷♂️
The last part makes me ill…. If they have to offer an EV version of the C9 due to EPA regulations….I’m not a fan…. and would never consider buying an EV “Corvette”…. A corvette is not a corvette without its V8 like a 911 is not a 911 without a flat 6. However if they continue to offer a V8 option we at least can still buy a real Corvette…. Besides being mid engine… the opportunity to buy a 500HP naturally aspirated V8 was another reason I bought a C8….
gm’s commitment to go all EV is now ten years away. And it’s not a switch where there’s a big supply of internal combustion vehicles available in 2034 and they all disappear in 2035…. The industry is going to look very different in 5 years and the prices are only going up…
Last edited by 24RiptideBlue; Jun 18, 2024 at 03:54 PM.
The last part makes me ill…. If they have to offer an EV version of the C9 due to EPA regulations….I’m not a fan…. and would never consider buying an EV “Corvette”…. A corvette is not a corvette without its V8 like a 911 is not a 911 without a flat 6. However if they continue to offer a V8 option we at least can still buy a real Corvette…. Besides being mid engine… the opportunity to buy a 500HP naturally aspirated V8 was another reason I bought a C8….
gm’s commitment to go all EV is now ten years away. And it’s not a switch where there’s a big supply of internal combustion vehicles available in 2034 and they all disappear in 2035…. The industry is going to look very different in 5 years and the prices are only going up…
I'll make you feel even worse! I read that 1174-page government report that outlined how the goals were set and gave some examples. A composite pic below. You can still get in on the internet.
But it alluded to what can be done to help force out ICE's. Higher gas tax! Yep, in Europe the $8.50/gallon of gas in Denmark is mostly Tax! Helps pay for all their giveaway programs! Have a Danish professor who has a Camaro. He pays thousands in taxes each year just to own it!
Note Silverado would have required about the same MPG as The Corvette. May not like it BUT it would have been in place starting in 2017! The folks behind this "cut CO2 emissions are still there! We'll see. I hvae read the report. Can disagree with the goals BUT each car family goal is based on science one car family to another.
I'll make you feel even worse! I read that 1174-page government report that outlined how the goals were set and gave some examples. A composite pic below. You can still get in on the internet.
But it alluded to what can be done to help force out ICE's. Higher gas tax! Yep, in Europe the $8.50/gallon of gas in Denmark is mostly Tax! Helps pay for all their giveaway programs! Have a Danish professor who has a Camaro. He pays thousands in taxes each year just to own it!
Note Silverado would have required about the same MPG as The Corvette. May not like it BUT it would have been in place starting in 2017! The folks behind this "cut CO2 emissions are still there! We'll see. I hvae read the report. Can disagree with the goals BUT each car family goal is based on science one car family to another.
The EPA loves the European approach and upcoming ban on internal combustion….
It would set this country back decades… strike that… generations… in standard of living. Basic transportation will be so much more expensive if internal combustion is regulated out of the market….
Long range trucking that supports the economy would be unrecognizable…. Shipments that take a few days would take a week or four times the number of trucks. Perishable loads that have to be refrigerated while transporting would take even longer as vital battery capacity goes into refrigeration vs motion.
The people driving these changes have no concept of thermodynamics and that a gallon of gasoline has 100 times the energy as the same volume of a best in the world, fully charged battery. Not 100 percent more…. 100 TIMES a more.
Ford lightning owners discovered this when they tried to tow their boat and the 320 miles of range dropped to 120…. or less….
Note to the EPA: the nations food supply is heavily dependent on the timely delivery of food before it spoils and the price of that food is heavily dependent on the cost to get it to the thousands of stores and markets coast to coast. How much will it cost to ship lettuce from CA to NYC in refrigerated EV trucks?
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
