GM small block AFM idea

[redhat]

Sitting here thinking — the new Gen VI small block that’s coming out. Inevitably will have AFM to meet CAFE requirements.

Wonder if a design such as a two-piece rocker arm would ever work. Rocker arm having one pivot point near the pushrod and another in the usual location with the trunnion. Utilize a system like a Honda variable lift where a hydrauliclly actuated pin locks the entire rocker arm to operate that valve when in V8 mode.

When not in V8 mode, the back half of the rocker would just pivot and go along for the ride.

Standard lifters in every lifter bore. Valves would stay closed when the cylinders not commanded. Of course cut fuel and spark to those cylinders. Oil would still travel through those lifters, and up through the push rod, even if that cylinder was deactivated, I don’t think from an oiling standpoint it would matter much if that extra flow was in the head.

Seems to me if you could keep potential failures to under the valve cover, you’d have a lot less of a headache when a failure occurs.

Wonder if something like this would ever work.

Would be sweet if Gen 6 had windows in the valley to change lifters.

 

[ctechbob]

Isn't that something similar to what Honda already does with VCM, except you're locking and unlocking cam followers, seems like it wouldn't matter where the motion was coming from, be it a cam or a pushrod:

"A solenoid unlocks the cam followers on one bank from their respective rockers, so the cam follower floats freely while the valve springs keep the valves closed. The system operates through controlling the flow of hydraulic engine oil pressure to locking mechanisms in the cam followers."

 

[joekingcorvette]

Just buy the range AFM disabler and buy a little more gasoline and make the engine last longer. I am sure there will be an aftermarket plug and play for that engine if one is not available already.

 

[redhat]

Just buy the range AFM disabler and buy a little more gasoline and make the engine last longer. I am sure there will be an aftermarket plug and play for that engine if one is not available already.

Sure, but I am thinking out loud about a better AFM. A disabler would still potentially be with a motor with AFM lifters that do fail.

 

[Snagglefoot]

For what is worth, AFM is still the accepted description for system, but in 2018 a new and hopefully more reliable system called DFM was released.

 

[JohnnyG]

Just read where this engine will be designed to meet very strict emission standards, including the required use of a particulate filter.
No thanks.

 

[AZjeff]

AFM was on 4 cylinders, DFM is on all cylinders in many different combinations. Twice as many parts spreading the load out over all cylinders. Better or worse? I was tracking AFM on GM truck forums, haven't paid attention to how DFM is doing. The best solution is probably still full delete if it really bothers you.

 

[MrHorspwer]

AFM was on 4 cylinders, DFM is on all cylinders in many different combinations. Twice as many parts spreading the load out over all cylinders. Better or worse? I was tracking AFM on GM truck forums, haven't paid attention to how DFM is doing. The best solution is probably still full delete if it really bothers you.

Decidedly hit-or-miss on DFM failures.

GM had a very big issue with lifter failures on late-2020 to late-2021 trucks. GM says that was foundationally a quality-spill caused by a poor metallurgy from the lifter supplier, not a result of the DFM system. Anecdotally, it seems 2019-2020 and 2022-2023 trucks have far less complaints in groups and forums, but they're still there now and again. There have been numerous polls too, with people self-reporting lifter failures, and the results are always 95% not having any issue at all. Of those that reported they had an issue, how many are the year of trucks GM said were affected by the quality spill and not an inherent DFM issue? I have an early-2020 truck and haven't had an issue.

It's inconclusive where DFM-disablers prevent failure. There are many people who report issues who say they've installed a Range or Pulsar on day-one. Again, how many of these were the trucks that bad lifters and would fail regardless?

As for full DFM deletes: It's tricky. First, the E90 ECM used in the 2019+ 5.3 and 6.2 is locked down hard and requires hardware modification to allow any type of tuning. HP Tuners offers an exchange service for $450 (this is a recent thing, it was originally $600 and the service was completely unavailable through most for 2022, so you couldn't do anything even if you wanted to spend the money).

Oil galley blocks offs and VLOM-deleted valley plates are readily available and LS7-style lifters drop in, but the camshaft is a problem. Using the stock DFM cam in will result in consistent misfires (also true with earlier AFM engine camshafts). With AFM engines, GM also made non-AFM engines that had similar cam profiles (use the camshaft from an L8T when deleting an L83). That's not true for DFM. There are no similar non-DFM cams anymore. That means you're in it for a real camshaft swap that would require actual tuning (I'm sure the aftermarket will eventually step in with a stock-style cam that doesn't require tuning).

While it can be done, older AFM-engines had kind of a formula to do a delete. The parts pick-list was out there and anybody with the mechanical aptitude to fix a failed lifter could also do a delete. I'm sure it will eventually get to that point with DFM-deletes but it's not quite there yet.

 

[AZjeff]

1 in 20 DFM having mechanical failure seems unacceptable. Any idea what the AFM fail rate is/was?

 

[4WD]

U.S. Now Requiring New-Vehicle Fleet to Average 49 MPG by 2026

Under NHTSA's new CAFE standards, total fuel costs are expected to fall, but new-car prices are expected to rise.

www.caranddriver.com

 

[tyman]

Decidedly hit-or-miss on DFM failures.

GM had a very big issue with lifter failures on late-2020 to late-2021 trucks. GM says that was foundationally a quality-spill caused by a poor metallurgy from the lifter supplier, not a result of the DFM system. Anecdotally, it seems 2019-2020 and 2022-2023 trucks have far less complaints in groups and forums, but they're still there now and again. There have been numerous polls too, with people self-reporting lifter failures, and the results are always 95% not having any issue at all. Of those that reported they had an issue, how many are the year of trucks GM said were affected by the quality spill and not an inherent DFM issue? I have an early-2020 truck and haven't had an issue.

It's inconclusive where DFM-disablers prevent failure. There are many people who report issues who say they've installed a Range or Pulsar on day-one. Again, how many of these were the trucks that bad lifters and would fail regardless?

As for full DFM deletes: It's tricky. First, the E90 ECM used in the 2019+ 5.3 and 6.2 is locked down hard and requires hardware modification to allow any type of tuning. HP Tuners offers an exchange service for $450 (this is a recent thing, it was originally $600 and the service was completely unavailable through most for 2022, so you couldn't do anything even if you wanted to spend the money).

Oil galley blocks offs and VLOM-deleted valley plates are readily available and LS7-style lifters drop in, but the camshaft is a problem. Using the stock DFM cam in will result in consistent misfires (also true with earlier AFM engine camshafts). With AFM engines, GM also made non-AFM engines that had similar cam profiles (use the camshaft from an L8T when deleting an L83). That's not true for DFM. There are no similar non-DFM cams anymore. That means you're in it for a real camshaft swap that would require actual tuning (I'm sure the aftermarket will eventually step in with a stock-style cam that doesn't require tuning).

While it can be done, older AFM-engines had kind of a formula to do a delete. The parts pick-list was out there and anybody with the mechanical aptitude to fix a failed lifter could also do a delete. I'm sure it will eventually get to that point with DFM-deletes but it's not quite there yet.

2021 AT4 25k Miles - Two Blown 6.2 Engines

2021 AT4 with 6.2 - $70k Vehicle 3700 miles blown engine - crankshaft. Warranty replacement. 25k miles blown engine - spun bearings. Warranty replacement. …and one pissed off consumer. Stay tuned.

www.silveradosierra.com

 

[53' Stude]

Sitting here thinking — the new Gen VI small block that’s coming out. Inevitably will have AFM to meet CAFE requirements.

Wonder if a design such as a two-piece rocker arm would ever work. Rocker arm having one pivot point near the pushrod and another in the usual location with the trunnion. Utilize a system like a Honda variable lift where a hydrauliclly actuated pin locks the entire rocker arm to operate that valve when in V8 mode.

When not in V8 mode, the back half of the rocker would just pivot and go along for the ride.

Standard lifters in every lifter bore. Valves would stay closed when the cylinders not commanded. Of course cut fuel and spark to those cylinders. Oil would still travel through those lifters, and up through the push rod, even if that cylinder was deactivated, I don’t think from an oiling standpoint it would matter much if that extra flow was in the head.

Seems to me if you could keep potential failures to under the valve cover, you’d have a lot less of a headache when a failure occurs.

Wonder if something like this would ever work.

Would be sweet if Gen 6 had windows in the valley to change lifters.

My brother works on lots of LS stuff. He removes this AFM stuff and fixes it correctly. He saw some bad experiences with it and said no way, not in my GM behicles

 

[OVERKILL]

For what is worth, AFM is still the accepted description for system, but in 2018 a new and hopefully more reliable system called DFM was released.

View attachment 137095

My understanding from some of the posts, I believe from @clinebarger is that DFM is objectively worse than AFM.

 

[tyman]

My brother works on lots of LS stuff. He removes this AFM stuff and fixes it correctly. He saw some bad experiences with it and said no way, not in my GM behicles

AFM delete ftw

 

[53' Stude]

AFM delete ftw

Yeah, I helped him do his 09’ Saab 9 7 SUV. We put a corvette cam and lifters in and did the “correct delete” and put a different tune in. Passes emissions every year and runs a LOT better

 

[PontiacHO]

I owned a 2008 Silverado 5.3 that had a lifter fail at 106,000 miles. Used Mobil 1 changed as per OLM. Since I’m a glutton for punishment I traded it on a new 2017 GMC Sierra with the 5.3. Use Valvoline Sythetic changed at 5,500 miles which usually corresponds with 35% of oil life remaining. 76,000 miles and no problems yet. Holding my breath. Not sure why but the 2008 Silverado AFM function was far less noticeable than the 2017 GMC. The 2008 was geared 3.73 and the 2017 is geared 3.42. Maybe that? Who knows…. If this one dumps the lifters I’m really not sure what Id replace it with. Have read the issues with Ecoboost cam followers and lifter failures with Ram. Toyota if I could find a good used one with the 5.7 V8 May be a sound choice. Probably should have went that way back in 2017. Life is full of second guessing.