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It sure sounds like it. I took a friend of mine for a ride and he has a lot of seat time in his fathers C7. We weren't talking and I said, "it just went into 4 cylinder mode" and he was in disbelief. He said he perceived absolutely nothing and it was noticeable in the C7. It went in and out several more times and he just shook his head at how transparent the whole system was.
Interesting thread..and I learned a couple of things from the DaveO yt video..I wanted to read more about the AFM valves because I talked to an employee of Borla exhaust trying to get more info about when they will release their cat-back system..It was the 2nd time we talked and the 1st.time he said the AFM valves were their biggest problem in engineering the exhaust system..He said their was a change from '20 to '21 and it was causing a CEL....I'm not sure if he was talking about the tension in that little rod that acuates the operation of the valves or a software change..Anyway, when we talked last week he was saying the system for the C8 will be coming out Mid May,and could be available in early June..I'm assuming they worked out the glitch with the AFM valves...now the 'bad' news....$4600.00 /$4800.00.. so more than the Fabspeed Valvetronic system...
Why would they delete it? It's a perfect combination of power and gas saver at same time. It's better than auto stop for sure. For somebody complaining of lifter failure, it is due to non synthetic oil use. My 2009 Escalade hybrid went up to 195,000 miles with no problems(it had AFM) and the second owner must have put more miles to it. My 2015i Escalade that was purchased new after trading the hybrid have the same AFM with no failures. How many miles now? 251,000 miles.
Don't know how on the C8's engine you can hear the Valves slam open in V4 mode. Seems GM has a different approach on AFM vs past.
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 AFM with 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.
Not arguing with you in the least, just trying to understand the logic. I did buy my C8 because it was 500 HP, but you can't drive WOT to redline all the time or even close, especially on the street. If the car is just loping along steady at 70MPH, why not enjoy the economy? If you even start to push the throttle it is back to a V8 in literally a fraction of a second. It's not like the pedal is on the floor and you're pulling levers to try and get the thing out of 4 cylinder mode and back to 8.
The point is the more complexity in motors the more stuff can go wrong. For me to save a gallon every 1000 miles is not worth having a feature that can cost a lot more to fix than what it saves you in fuel.
That is why I dislike all these new gadgets they put on cars these days as they are built to break and keep the spare parts department turnover going. This is across all car manufacturers. Most of the time a plastic 20c piece fails and they will sell you a complete assembly for 600.
The point is the more complexity in motors the more stuff can go wrong. For me to save a gallon every 1000 miles is not worth having a feature that can cost a lot more to fix than what it saves you in fuel.
That is why I dislike all these new gadgets they put on cars these days as they are built to break and keep the spare parts department turnover going. This is across all car manufacturers. Most of the time a plastic 20c piece fails and they will sell you a complete assembly for 600.
What is there to fix? It has been proven to be reliable. I have proven it to be bulletproof at least up to 200,000 + miles. I don't think there is a sports car that you know can reach that milestone.
What is there to fix? It has been proven to be reliable. I have proven it to be bulletproof at least up to 200,000 + miles. I don't think there is a sports car that you know can reach that milestone.
I guess all the collapsed lifter talk out there because of AFM would have happened even without AFM. Good to know you have proven it to be bulletproof.
Pretty sure they are talking about AFM valves in the exhaust system, not valves in the cylinder heads.
Why would you have AFM (Active Fuel Management) valves in exhaust system? How would that improve Fuel Economy?
Now Aftermarket Exhaust, on an C8's Engine could have a problem. The Cats on the C8 are a different design than what Older Gens came with. I believe the C8 uses a Direct Couple design, designed for extrema heat of being mounted directly to the Header pipe, Vs older style that are mounted downstream from header. If you go back to 2019 posts about engine/exhaust system setup you'll see what I'm talking about. You'll find a breakdown showing where they are mounted. They are designed for extrema heat, Vs ones on prior gens. They also are not as restrictive as the old style ones. .
Re-Read the NPP / AFM post. One is Exhaust. AFM is Active Fuel Management.
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.
Could AFM effect how aftermarket exhaust works The CATS on the C8 are different than the ones on Previous Gens. They are a different design, than previous Gens, because of the extrema heat they have to withstand, for one they bolt to the Headers rather than downstream.in exhaust pipe. I forget what they are called. If you go back to early post about exhaust system back in 2019 you will see what I'm talking about. .
Last edited by Poorhousenext; May 2, 2021 at 05:13 AM.
Why would you have AFM (Active Fuel Management) valves in exhaust system? How would that improve Fuel Economy?
Now Aftermarket Exhaust, on an C8's Engine could have a problem. The Cats on the C8 are a different design than what Older Gens came with. I believe the C8 uses a Direct Couple design, designed for extrema heat of being mounted directly to the Header pipe, Vs older style that are mounted downstream from header. If you go back to 2019 posts about engine/exhaust system setup you'll see what I'm talking about. You'll find a breakdown showing where they are mounted. They are designed for extrema heat, Vs ones on prior gens. They also are not as restrictive as the old style ones. .
Re-Read the NPP / AFM post. One is Exhaust. AFM is Active Fuel Management.
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.
Could AFM effect how aftermarket exhaust works The CATS on the C8 are different than the ones on Previous Gens. They are a different design, than previous Gens, because of the extrema heat they have to withstand, for one they bolt to the Headers rather than downstream.in exhaust pipe. I forget what they are called. If you go back to early post about exhaust system back in 2019 you will see what I'm talking about. .
You're still not getting it. The valves you are referring to ARE the valves in the heads. They are just the valves in the heads, NOT some special AFM valves, just valves like the ones in the other cylinders. The valves in the heads get closed by the AFM lifters closing off the cylinder and making it an air spring. There ARE AFM valves in the exhaust system that are simply flap valves that open and shut to redirect exhaust gasses. These are the valves everyone here is talking about.
You're still not getting it. The valves you are referring to ARE the valves in the heads. They are just the valves in the heads, NOT some special AFM valves, just valves like the ones in the other cylinders. The valves in the heads get closed by the AFM lifters closing off the cylinder and making it an air spring. There ARE AFM valves in the exhaust system that are simply flap valves that open and shut to redirect exhaust gasses. These are the valves everyone here is talking about.
Maybe I don't.
I'm going by the Original Subject of this thread.
So the C8 has Air Flow Management valves in the Exhaust System that re-direct air as means to increase Fuel Mileage! .
I digress to you on that. Something I had no idea GM was doing, to help meet CAFE Standards. learn something new every day about the C8.
I'll give you one.
If you engage Cruise Control at posted speed limits (I'm sure it will work above posted speed limits as well), when approaching some grades, if you will ease down on the Throttle Pedal slightly with your Foot, you can keep the engine from disengaging V4 mode by just adding a little more fuel to engine. Try it.
Goes along with with when your going down hill, engine will go back to V8 mode to Engine Brake to help maintain cruise control speed going down inclines. I use cruise to stay within Posted Speed limit on the hilly roads around here to stay within posted Speed Limits, as some Towns or Counties have a speeding ticket quota Officers are suppose to meet.
I'm not very popular during rush hours...LOL
Last edited by Poorhousenext; May 2, 2021 at 10:40 AM.
Heck that is why they had "skip shift" in my manual C6 and 2 C7, M7s. No one shifts at the very low rpm's the C7 Owner's Manual said to change gears for max mpg. Skip Shift forced a shift from 1st to 4th is shifting below 17 mph ONLY to better mpg. EPA allowed GM to use that in their EPA cycle required test as it was built into the car! Yep for $20 could defeat Skip Shift and since I never have my 2 C7's in ECO Mode had no V4 Mode. In fact the few times I tried ECO on the Interstate it was a bit jerky going back and forth.
However as other's have stated when I drive my C8 in My Mode it does engage and is a non issue. They slip the clutches slightly and you don't feel a thing.
Now when I drive in Z MODE Power Set To Track, with set MRC RIDE set to Sport - it never comes in. Your choice.
Why would you have AFM (Active Fuel Management) valves in exhaust system? How would that improve Fuel Economy?
Now Aftermarket Exhaust, on an C8's Engine could have a problem. The Cats on the C8 are a different design than what Older Gens came with. I believe the C8 uses a Direct Couple design, designed for extrema heat of being mounted directly to the Header pipe, Vs older style that are mounted downstream from header. If you go back to 2019 posts about engine/exhaust system setup you'll see what I'm talking about. You'll find a breakdown showing where they are mounted. They are designed for extrema heat, Vs ones on prior gens. They also are not as restrictive as the old style ones. .
Re-Read the NPP / AFM post. One is Exhaust. AFM is Active Fuel Management.
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.
Could AFM effect how aftermarket exhaust works The CATS on the C8 are different than the ones on Previous Gens. They are a different design, than previous Gens, because of the extrema heat they have to withstand, for one they bolt to the Headers rather than downstream.in exhaust pipe. I forget what they are called. If you go back to early post about exhaust system back in 2019 you will see what I'm talking about. .
Originally Posted by DJGold
I removed my afm valves on my aftermarket exhaust using the cicio bypass. And not surprisingly its not seamless. 🤣
Hmm, foolish in a C8, accomplished nothing!
Originally Posted by Poorhousenext
Maybe I don't.
I'm going by the Original Subject of this thread.
So the C8 has Air Flow Management valves in the Exhaust System that re-direct air as means to increase Fuel Mileage! .
Hmm, some confusion! Pic shows what valves are used for what and where they are.
1st the Exhaust valves that only partially close in V4 mode and do NOT divert exhaust, they just provide increased back pressure. That is partly done so the V8 doesn't sound like one missing on 4 cylinders. The extra back pressure helps with V4 performance.
The Exhaust valves that divert where is goes are only on cars with NPP. They do essentially bypass the muffler when shut. They are ONLY open or shut controlled by a computer.
The engine valve lifters that control V4 Mode are very similar to all hydraulic lifters BUT can be controlled with valves to allow them to essentially collapse when cam lift is applied rather than operate the cars intake and exhaust valves. There is a very complex sequence that defines when they operate so as to keep cylinder to avoid pumping losses. There is a full page describing when and how they activate I won't bother to post! You're welcome!
meanwhile China and India dont have to do sh^t..lol If they want to do away with gas they better get those fission reactors on line asap. I wonder what magic they will do the for the E-ray.. maybe at driving speed shut the engine off and run the motors in the front .. FW drive corvette..lol..
^^
Hmm, I am one to complain about China and India using ~75% coal to generate electricity where we use ~20% BUT V4 mode is a non issue in the C8, it is total non intrusive.
The E-Ray as it's now called was defined in a November 2019 post that had a link to the leaked info. Yep to get to the ~40 mpg that would have been required in 2025 for all Vettes and other sports car's it would, like many hybrids:
In normal cruising (GM will turn on the software to get much higher mpgONLY when a government dictates, beit US Federal, California etc) will get to ~30 mph with the FWD electric motor before tuning on the ICE. It would recharge the battery that article and subsequent info on what is now called and E-Ray showed is located in the center support structure. That recovers a lot of the 1/3 of the power that gets to the rear wheels wasted when braking. (BTW only about 20% of the energy in gasoline gets to the rear wheels to propel the car, the remainder goes to wasted heat.)
When driving in anger. at wide throttle openings both the ICE and FWD electric power can be used as EPA does not measure mpg (as now) at large throttle openings, only need enough to meet their speed cycle requirements.
Don't have to like it, but was to become law starting in 2017. Doesn't look like even 40 mpg will not be good enough for the no fossil fuel crowd. The C9 will be an EV Vette!
Pic from leaked article that was on the forum in November 2019. Black text was put on pic by me and is from info in the article.
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.
