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Under the old 2012 EPA Plan it works that way. Porsche stated publicly their plan was to have 50% EV "sports cars" in 2025. Ferrari press release said they thought batteries were not good enough to have sports car EVs so was planning on having Hybrids. In an interview before the pandemic, Ferrari CEO Camillari said they wanted 60% of Ferrari’s sold in 2022 to be hybrids! Takes mostly software to turn a "Performance ONLY Hybrid" into forced Stop/Start and the ICE turning on when the electric motor brings it to ~45 mph. That is all that is needed for the EPA test that takes only ~75 hp and small throttle opening to achieve in a Vette. The advantage is with large throttle openings you still get power from both. EPA doesn't measure mpg at say WOT! In fairness it's not "on average" how folks drive.
Unfortunately, things have changed after the pandemic and the 2012 EPA plan stopped by a Pen! Now the goal posts have moved to ONLY zero fossil fuels will do. Silly but that is the plan. We'll see just what the April 2022 EPA announced plan of requiring 49 mpg in 2026 versus the old plan average (announced in a Press Release) of 54 mpg in 2025 means when details are released. I expect that will NOT be revealed until January 2025!
PS: That 1174-page report has very detailed criteria about how a "Model is Classified in a Family" Can't just call a Cayenne SUV a Porsche (as they do) and get credit. It's very well written. Two seat sports cars can be grouped together. Nope, GM could not just call a Volt a Corvette and get credit!It has a square foot area component (see below table and footprint column) and other factors. They show statistically why they picked certain criteria, like footprint. It's an indirect indicator BUT they found it combined several others. Lots of Math. It's also NOT the manufacturers average. Ferrari can't just buy Tesla and meet the requirement! And Ferrari would not be penalized because they don't make "grocery getters!"
It has a hp as well as number of passengers component. You'll see below the Vette 39 mpg, a 500 hp Mustang only required 31 mpg. I think partly because of the 100 more hp and 4 seats. Appeared A Toyota Corolla had that 60-mpg goal because with its 126 hp it could achieve that number! Note the "footprint value." They show statistically why they used that value based on what cars have achieved. A Prius at the time could achieve a high number.
St. Jude Donor '12-'13-'14-'15-'16-'17-'18-'19-'20-'21
Originally Posted by CBC7
Is there any way to disable the active fuel management on the C8? I have a Range Technology AFM disabler on my C7 and love it. I checked their website a while ago and did not see one for the C8.
AFM and how to "defeat" seems a popular, recurring topic that often leads to "interesting" speculation.
Firstly, I very highly doubt that AFM causes lifter failure. Some version of cylinder deactivation technology has been in GM vehicles since at least 1987, starting with Cadillac models with "displacement on demand," the forerunner to AFM.
Secondly, the lawsuit someone posted a video of in this thread is still making its way through the court system. Given how long this technology has been in GM vehicles, it might be an uphill battle.
Here is a link to the most recent developments on the lawsuit that I could find on the net.
Thirdly, I highly doubt that Range Technology or any other aftermarket company will develop a device to defeat AFM, given the difficulty (five model years in) in cracking GM's Global B architecture with encrypted bus communications.
Lastly, members should check the archived "Ask Tadge" sub-forum before posting their disdain for AFM on the LT2 engine in the Stingray.
We know some customers are not fans of AFM (Active Fuel Management, otherwise known as cylinder de-activation). They worry it will sound bad, or feel bad as it transitions in and out of V4 mode, or just don't like that the engine doesn't always run on all cylinders. Manufacturers around the world are being put under tremendous pressure to reduce fuel consumption and greenhouse gases. As a result, you see a massive move to electrification, hybridization and small displacement charged engines. General Motors is fully embracing the initiative and has a stated goal to get to a zero emissions future.
So how does Corvette fit into this picture? Even before global greenhouse gas concerns became mainstream, Corvette prided itself on efficient operation. After all, low mass, low drag and efficient engines make for a better sports car. There are a lot of ways to get fuel efficiency and some of them negatively impact the driving experience. Our manual transmission skip-shift we had for years was not a customer favorite, but it helped economy and kept us away from gas-guzzler taxes. The bottom line is that we have to make choices that balance the owner's experience (including operating cost) and our impact on the planet.
Our AFM system is very effective on the small block V8. It lets us close the valves on the de-activated cylinders so the cylinders act as air springs. When the engine rotates we get energy back as the compressed air in the cylinder expands. Other manufacturers just stop fueling the de-activated cylinders and so don't get much fuel savings. The reason 4-cylinder operation is more efficient is that the active cylinders are worked harder with a greater throttle opening. That's like taking a restrictor out of the system saving pumping losses. On Corvette, AFM saves more fuel than start/stop, a feature becoming very prevalent in the marketplace. For many cars, start/stop is a great choice because it is almost transparent to the occupants. Not so on a Corvette. Our engine has a lot of character, so when it stops running it is very noticeable. We have received a lot of very strong input from customers that they would not like it.
One of the innovations on the 2020 Stingray is the integration of AFMwith a DCT. We a quite proud of how seamless we've been able to make it. We believe we are getting the efficiency benefit with virtually no compromise to the driving experience. Numerous drive impression articles have been written and I do not remember reading any negative comments about it. Bottom line is that we must balance conflicting demands and make smart choices so we can continue to offer the driving pleasure of a naturally aspirated V8 engine.
So now to the heart of your question. Yes, when you are in manual mode the engine stays in V8. That is true either by hitting the "M" button or by entering "temporary tap" by pulling one of the paddles. Temporary tap will revert to "Drive" after about 5 seconds if you don't request an additional shift in that time. AFM is also de-activated in "Track" mode. Since PTM is only available in Track mode, the answer is yes to that one too. If you are in PTM, it will be V8 only. New for 2020 is the "Z" mode which will come from the factory set up as an extra sporty mode including shift schedules pulled from the "Track" mode, so that will be V8 only. Of course, you can customize "Z" mode any way you want, so if you elect another shift pattern, AFM will return.
Why GM couldn't make AFM something that could be turned off easily (read: without going into a mode like track mode or manual mode after startup):
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 "AFMoff" 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 AFMeverywhere 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.
Interesting banter about AFM in this thread, as usual, but the bottom line (and the point of my post) is that GM was very clear on why AFM is on this vehicle.
Like it or not, AFM is part of the package with buying a Stingray or an E-Ray. For those who don't like AFM, you only have four options...
1. Buy a Z06. 2. Drive in manual mode 100% of the time. 3. Set your Z-Mode shift pattern to Track. 4. Sell (or don't buy) your Stingray.
The reality is that AFM is part of the car, and for one to find it incredulous that a V8 should ever have cylinder deactivation is a bit shortsighted, in my opinion, because it ignores the corporate realities that GM has to deal with.
I think it is nice that I can get upwards of 30 MPG and still have nearly 500 horsepower at my disposal at any given time.
This discourse seems to come down to sports car purists and those who view and use their C8 as a daily driver or GT cruiser (like me). Most people in the latter camp don't have a problem with AFM. Most in the former camp have major problems with it. The Z06 is what you want if you are in the former camp.
I have a Z06 on order and am contemplating whether or not I will follow through and complete the purchase when it arrives. I love my C8 Z51 Stingray; it is the ultimate GT cruiser that can be driven daily.
I commend GM and the fine folks at Team Corvette for offering many options to satisfy the GT cruiser/daily driver crowd and the sports car purist. The key is understanding those options, how they fit your lifestyle, and how you intend to use the car.
Same 4 every time. But how much stress it is it? It only kicks in with steady cruising - at constant speed. Anything more than the mildest acceleration, or slightest incline causes it to revert to v8 mode. And it also returns to v8 mode with foot off the throttle. So its only steady cruising. .
I agree in general, but I'm surprised at how often it will switch to V4 mode in Tour, even driving around in the suburbs. It doesn't stay in V4 very long since you tend to frequently change speed, but it does go into 4 cyl operation. But that kind of supports your argument that it doesn't spend a lot of time in V4 mode. In addition to what you wrote above, even in steady cruise it won't stay in V4 for more than 10 minutes before it switches back to V8 for 1 minute (that's in the LT1, and I'm pretty sure the LT2 is the same). GM's documentation says thats to equalize cylinder temperatures, not because of wear concerns.
Great explanations; thank you. My only question left is if there are any additional hardware to implement AFM, or it's all purely software (shutting off injectors, changing valve timing, etc)? I wouldn't like any more crap that could go wrong. This seemingly low-tech pushrod engine is already complex enough with the VVT crap. Not to mention an unproven DCT transmission (all others had issues the first few years, so nothing unique to Tremec), but other than requiring ridiculous maintenance, seems to be fairly reliable so far. Thanks gang.
Great explanations; thank you. My only question left is if there are any additional hardware to implement AFM, or it's all purely software (shutting off injectors, changing valve timing, etc)? I wouldn't like any more crap that could go wrong. This seemingly low-tech pushrod engine is already complex enough with the VVT crap. Not to mention an unproven DCT transmission (all others had issues the first few years, so nothing unique to Tremec), but other than requiring ridiculous maintenance, seems to be fairly reliable so far. Thanks gang.
Sorry to drag up an old thread, I was searching for an answer to this topic... I don't care about fuel economy. If I did, I would have gotten a Prius... My concern with AFM/DFM is lifter failure. LOTS of 5.3 and 6.2 motors have suffered from it, there are class action lawsuits over it, etc...
On my Silverado's, I always just tossed in a Range box into the OBD port to disable it, as was suggested to me by my Chevy dealers service manager...
So I guess the "fix" with the new C8's is to just drive it in track mode or set Z mode to use Track shift points, and that will just force it to always stay in V8 mode?
AFM disabler is a gimmick but I think the AFM system has greatly improved over the years. I had a 17 Grand Sport that had a range disabler in it from new and had catastrophic lifter failure at 40k miles.
So I guess the "fix" with the new C8's is to just drive it in track mode or set Z mode to use Track shift points, and that will just force it to always stay in V8 mode?
There is nothing to "fix" as AFM in the C8 has not been shown to be a problem....
There is nothing to "fix" as AFM in the C8 has not been shown to be a problem....
Ahh.... I know its been a problem in a lot of GM cars and trucks over the years, and I had seen some cases with the C8... Wasn't sure how wide spread it was...
Ahh.... I know its been a problem in a lot of GM cars and trucks over the years, and I had seen some cases with the C8... Wasn't sure how wide spread it was...
I have not heard of any cases with problems linked to the C8s AFM...
AFM was an issue in some earlier vehicles but those issues have been addressed.
Myself, I never had any issues. Had a 2007 Avalanche which had the first iteration of AFM in it, had some issues with oil usage which was fixed by a couple of recalls, but no lifter failures, put over 100k on that truck
Currently have a 2104 Silverado with almost 90k on it and no lifter failures.
Sorry to drag up an old thread, I was searching for an answer to this topic... I don't care about fuel economy. If I did, I would have gotten a Prius... My concern with AFM/DFM is lifter failure. LOTS of 5.3 and 6.2 motors have suffered from it, there are class action lawsuits over it, etc...
On my Silverado's, I always just tossed in a Range box into the OBD port to disable it, as was suggested to me by my Chevy dealers service manager...
So I guess the "fix" with the new C8's is to just drive it in track mode or set Z mode to use Track shift points, and that will just force it to always stay in V8 mode?
I simply drive in “M” all the time. It’s never been in Drive mode because I like to paddle shift. After all, it is a sports car.
Sorry to drag up an old thread, I was searching for an answer to this topic... I don't care about fuel economy. If I did, I would have gotten a Prius... My concern with AFM/DFM is lifter failure. LOTS of 5.3 and 6.2 motors have suffered from it, there are class action lawsuits over it, etc...
On my Silverado's, I always just tossed in a Range box into the OBD port to disable it, as was suggested to me by my Chevy dealers service manager...
So I guess the "fix" with the new C8's is to just drive it in track mode or set Z mode to use Track shift points, and that will just force it to always stay in V8 mode?
There is no evidence that that the LT engine AFM lifters have more failures than the non-AFM lifters.
There is no evidence that not using AFM prevents AFM lifter failure.
But, yes, if you drive in Track mode or Z-Mode when the powertrain is set to Track then AFM won't engage.
Only good thing about it is that it does indeed get great highway mileage. I hit 30 mpg recently.
When driving in MY Mode never heard it! Only way I know it switched is the dash display.
Now in fairness wife seldom was in my C8, for her to complain! 99% of all other times my sound system is playing >1500 songs in shuffle mode to drown out tire and road noise. Although cabin is quieter than my two C7s, still plenty of tire/road noise.
Have tried opening window to hear with sound system off. Can't.
BTW from my two standard shift C7s never in ECO so no V4 but did test mpg on Interstate several times. Exact same 20 mile stretch with cruise control, ~1 1/2 mpg better. What GM needs for better EPA mpg but not that big a deal. For fixed 65 mph speed still need exact same hp!
Ahh.... I know its been a problem in a lot of GM cars and trucks over the years, and I had seen some cases with the C8... Wasn't sure how wide spread it was...
Any time someone has a valve or lifter issue they blame it on AFM. Lifters can fail in any car, with or without AFM, and occasionally they do. I haven't seen a single post here or on MECF documenting a lifter failure on an LT2. There are literally hundreds of millions of miles on AFM equipped small blocks and lifter failures are very rare.
Ahh.... I know its been a problem in a lot of GM cars and trucks over the years, and I had seen some cases with the C8... Wasn't sure how wide spread it was...
You've seen problems with the C8, really, because nobody on here has, not one. As far as it being widespread, it's non existent.
Disabling AFM in previous models or driving it in manual and track mode to prevent it going into v4 makes no difference either. The reason for failures in early generation afm cars or trucks was lubrication. It had nothing to do with cylinders shutting down. The C8 and all other GM vehicles have not had AFM failures like before. Crap everyone is posting is from 5-10 years ago and not today. Post data on AFM failures in the past few years.
09-24-2023, 11:08 AM
