AFM/DoD Delete Advice Needed

[Marky Dissod]

The LMG specs I can find are:
*Duration @ 0.050in (int/exh): 193 deg/193 deg *Lift (int/exh): 0.482 in/0.482in *Separation: 116 deg *Cam gear: 1 bolt

While the LM7 specs are:
*Duration @ 0.050in (int/exh): 191 deg/190 deg *Lift (int/exh): 0.457 in/0.466 in *Separation: 114 deg *Cam gear: 3 bolt

Those are pretty different cams, aren't they?

Congratulations, you're right, Kwing, you're still in the game.
Try using Summit specs?

Intro to the LY2, L20, LY5, LMG, and LMF · Help Center

https://help.summitracing.com/knowledgebase/article/SR-04859/en-us

Chevy LY5 Engine Specs · Help Center

Chevy LMG Engine Specs · Help Center

I used to eat lots of cookies, but prediabetes has me scared of cookies now, and I ain't schadt on the floor yet.

 

[mikez71]

Someone is going to have to come up with information that convinces me you can’t install non AFM lifters on this AFM camshaft as long as you use the correct push rods.

For our AFM engines, the pushrods are the same length for all cylinders?
That makes me think the difference in the cam lobe would only be the base circle diameter to makeup for lifter height difference?
Ramp profiles should be identical?

But HOTROD magazine says "AFM lifters have nearly 0.010 inch of movement before their inner mechanism locks, requiring a much softer cam profile"
In which case I suppose AFM valves don't open exactly the same as non AFM valves anyway?

Using different length pushrods, there may be a slight geometry difference as the pushrod rocks?
Being that the angle is very minimal, it may be un-noticeable..
But it sounds like the AFM cylinders have more lift and duration than the standard cylinders, while ramping up slower.
There's more imbalance than I first thought..

 

[rdezs]

Here's a good article from Speedway motors that addresses the issue. Screenshot below, but here is the link to the whole article.

Screenshot of relevant info:

Of course, you can experiment all you want. Just be advised that if it fails, it can often be catastrophic to the engine. You may end up with a big paperweight and looking for a new block.

 

[Kwing]

The cams are different, just measure.

I think it's pretty obvious at this point that this is the only way we'll get a straight, reliable answer. Not for lack of trying or ill intent, but just because GM makes it too hard to get the information needed.

But I don't even need to measure AFM vs non-AFM like I suggested at the beginning. I just need to measure the AFM cam that's in it.

It's real simple - either all the lobes are the same and the "must replace" guys are wrong, or the AFM lobes are different, and the "must replace" guys are right.

May be a couple weeks before I have data to share, but stay tuned...

 

[Marky Dissod]

either all the lobes are the same and the "must replace" guys are wrong, or
or the AFM lobes are different, and the "must replace" guys are right.

Part time / AFM lobes are slightly but meaningfully different from full time lobes, because AFM lifters are not the same as more reliable lifters.
After about 2 decades, this is a 'known known'.

 

[Kwing]

After about 2 decades, this is a 'known known'.

"Known" seems to be a relative term in this discussion, LOL. If it is so well known, why the heck are there ZERO numbers available about what's different?

Maybe you're right, and it IS true, I can't say either way yet, but I can say I need more than "it just is" before I can believe it with all the contradictions flying around . So I'll find out within the next couple weeks...

 

[West 1]

Shops that re grind cams had a cam profiler in house. They could measure the lobes and determine exactly what the lift, duration etc was for any camshaft.

Re grinding old cams to new profiles was standard up till the late 1980’s when new cams got so cheap it was better to buy the new cams than regrind. Most regrinding stopped in that period of time. Not sure if any of the old shops still have the profiler avaiable.

The AFM cams are close enough that owners work these engines hard with zero problems. Towing 7500 pound trailers the afm is not engaged for long periods of heavy work. The engine does not run badly. If the lobes are different as stated they are close enough to help the AFM work while not being detected by the driver.

 

[rdezs]

Lol ... Following that logic, you should be able to stick your AFM lifters in the non AFM cylinders and crank that engine up.... If your theories correct, it will run well. If not it will self-destruct rather quickly.

Some people find it difficult to accept all the knowledge of what works, for whatever reason. The configuration and layout of the pre-afm LS engine is a known rock solid commodity. Taking the AFM design back to the original is a no-brainer.... For most people.

 

[Kwing]

Taking the AFM design back to the original is a no-brainer.... For most people.

Just curious, can you point out for me who in this thread has tried to argue the system should stay as-is? I mean, that's the 2nd time you've implied that, so I'm just hoping you can show me what I'm missing?

 

[Fless]

Some people find it difficult to accept all the knowledge of what works, for whatever reason. The configuration and layout of the pre-afm LS engine is a known rock solid commodity. Taking the AFM design back to the original is a no-brainer.... For most people.

I read "original" as "pre-afm," that is, full AFM delete and conventional cam/lifters etc.

 

[rdezs]

Yes. What the LS engine was before GM engineers came up with this AFM garbage.

Leaving it "as is" refers to leaving any part of it in place. An OBD2 plug in disabler has its uses....for example, to turn it off while a person makes plans on the hardware delete....but as a permanent solution leaving the hardware in place, carries a degree of risk. As for 'who', there's been references to leaving various parts as it ...like the camshaft. It's been tried multiple times over the years. Recall reading about rather quick failures. My view is simple ... if you are going to do something, do it right. What is 'right?' The configuration that worked damn near perfect before these components were introduced. The data is there...and I assumed it was common knowledge.

 

[mikez71]

Lol ... Following that logic, you should be able to stick your AFM lifters in the non AFM cylinders and crank that engine up.... If your theories correct, it will run well. If not it will self-destruct rather quickly.

I wouldn't be shocked if stock lifters plus longer pushrods could run well enough on an AFM cam, and not self destruct quickly.
But I also wouldn't be shocked if it does not run perfectly well..
Seems to be instances where some said it ran "fine" and others had misfires.

The AFM cams are close enough that owners work these engines hard with zero problems. Towing 7500 pound trailers the afm is not engaged for long periods of heavy work. The engine does not run badly. If the lobes are different as stated they are close enough to help the AFM work while not being detected by the driver.

Agreed, all articles point to the cam lobe compensating for the locking mechanism and increased lash of an AFM lifter.
But AFM motors still idle smooth and rev fine and most? go over 200k miles.
I assume a standard lifter with AFM cam would open slightly sooner with more lift, due to having less lifter lash.

"Known" seems to be a relative term in this discussion, LOL. If it is so well known, why the heck are there ZERO numbers available about what's different?

I'm guessing because most people just switch to a standard cam and call it a day.
What's anyone really going to use the AFM cam information for, other than satisying their curiousity?
If I wanted to save money/time/labor, I would replace just the one faulty AFM lifter with another AFM lifter. (assuming cam is in good shape)
There have been cases where the standard lifter failed before the AFM lifter afterall..

A little info according to blindsquirrel on hptuners forum...

Lobe Lift 1-4-6-7 (DoD) 0.289
Lobe Lift 2-3-5-8 (non-DoD) 0.283

From google..

Attribute	AFM Lobes (Cylinders 1, 4, 6, 7)	Normal Lobes (Cylinders 2, 3, 5, 8)
Tappet/Lobe Lift	~0.286" lift (higher)	~0.275" lift (lower)
Duration & Timing	3° to 4° longer duration; valves open earlier.	Shorter duration; standard ramp rates.
Ramp Profile	Smoother, specialized take-up ramps designed to absorb the ~0.010" of mechanical slack inside a collapsible AFM lifter before it locks.	Aggressive, standard hydraulic roller ramps optimized for direct, rigid valve action.

• The Extra Lift (~0.011"): The AFM lobes feature higher lift and longer duration at the camshaft to overcome internal compliance. The special collapsible AFM lifters naturally absorb about 0.010" to 0.015" of mechanical slack and oil compression inside their internal locking pins before they completely rigidize. The extra lobe lift ensures that after losing some motion to the lifter, the actual valve open height matches the normal cylinders. [1, 2, 3, 4]
• The Massive Take-up Ramps: The AFM lobes feature highly extended, gradual base-circle ramps. This slow-opening ramp design slowly picks up that mechanical slack inside the lifter to prevent the internal locking pins from slamming violently, protecting the valvetrain components from shattering. [1, 2]

If you use a solid standard lifter on these AFM lobes during a delete, the valve opens way too early, opens too high, and slams closed roughly—instantly triggering uncorrectable misfires. [1, 2]

 

[rdezs]

Very true.... regular lifters have in fact failed before AFM ones, just nowhere near as common

 

[Kwing]

If you use a solid standard lifter on these AFM lobes during a delete, the valve opens way too early, opens too high, and slams closed roughly—instantly triggering uncorrectable misfires. [1, 2]

So... magic mushrooms for this guy then? https://www.tahoeyukonforum.com/threads/dod-delete-theory.147084/

And there's my problem, right there. The evidence against the cam needing to change is just as strong as the evidence for it. Near as I can tell, the only difference is the size of the egos.

So, like i said, I'll prove it or disprove definately by measuring it.

Until then, particularly if your go-to is quoting Google, which has contradicted itself god knows how many times just for me today on the subject* continuing to beat the dead horse with no more evidence than "it just is", "because i said so", or "because you're a stupid poopy face" is nothing but chest pumping overcompensation, further evidenced by the pompus, condesending tones being used.

Prove it, or STFU

 

[mikez71]

OK I shouldn't have quoted google.
But most of that information is what I've seen in various forums anyway. You should have said you want to talk to the GM engineers that designed it.

Why the **** do I need to prove anything to you? I was only speculating based on what I assumed to be logical widely accepted data. So you're right, I don't KNOW anything for a fact. Since you keep saying we don't know shit, why don't you prove us wrong?

Since none of us are up to your high analytical standard, who don't you measure it and get back to us with the results, and whether or not you want to change the cam?

Nobody else has this much trouble deciding, but maybe everyone else is an idiot, or doesn't have your special circumstances?

Sorry I can't explain why that guy had magic mushrooms. Maybe some people didn't change pushrod length, maybe some people think it runs great when it doesn't, maybe there's more than one type of AFM cam. But keep being upset because we're all dumb and don't know all the specifics, OK?

Also, feel free to point out where I was pompous or condescending before this post.

 

[rdezs]

That's not even close to being evidence of anything. Reported it as an immediate misfire, then nothing in over 2 years..... And why on Earth when anyone go to this much trouble using hardware that is known to fail way too early. Absolutely nothing to gain.

 

[West 1]

Attribute	AFM Lobes (Cylinders 1, 4, 6, 7)	Normal Lobes (Cylinders 2, 3, 5, 8)
Tappet/Lobe Lift	~0.286" lift (higher)	~0.275" lift (lower)
Duration & Timing	3° to 4° longer duration; valves open earlier.	Shorter duration; standard ramp rates.
Ramp Profile	Smoother, specialized take-up ramps designed to absorb the ~0.010" of mechanical slack inside a collapsible AFM lifter before it locks.	Aggressive, standard hydraulic roller ramps optimized for direct, rigid valve action.

• The Extra Lift (~0.011"): The AFM lobes feature higher lift and longer duration at the camshaft to overcome internal compliance. The special collapsible AFM lifters naturally absorb about 0.010" to 0.015" of mechanical slack and oil compression inside their internal locking pins before they completely rigidize. The extra lobe lift ensures that after losing some motion to the lifter, the actual valve open height matches the normal cylinders. [1, 2, 3, 4]
• The Massive Take-up Ramps: The AFM lobes feature highly extended, gradual base-circle ramps. This slow-opening ramp design slowly picks up that mechanical slack inside the lifter to prevent the internal locking pins from slamming violently, protecting the valvetrain components from shattering. [1, 2]

If you use a solid standard lifter on these AFM lobes during a delete, the valve opens way too early, opens too high, and slams closed roughly—instantly triggering uncorrectable misfires. [1, 2]



This is the first time I. have seen information on the cam lobes giving details and this does make total sense. In the past I have seen and read many comments but never saw facts to back it up. So I was wrong saying the AFM cam would run just fine on standard roller lifters. The company I worked for owned Johnson Hylift lifters so I knew quite a bit about lifters but we sold that business off before AFM lifters came to be. Always something to learn. I should go back and edit my previous post to avoid misleading any other readers.

 

[mikez71]

Another source not referenced in the google response, where 'Stroked 4.8L' took measurements of a gen5 engine back in 2014.

2014 5.3L camshaft specs - PerformanceTrucks.net Forums

GMT K2xx Trucks General Discussion - 2014 5.3L camshaft specs - Does anyone have or know the 2014 5.3L camshaft specs? Iv'e search but can't find what I want. I'm looking for the full specs on the cam, Like; Valve Timing: .006 Duration: Intake - 260* Exhaust - 266* Lobe Separation: 115* Duration...

www.performancetrucks.net

There are more measurements in the link, but below are the only measurements regarding cam profile.

•Camshaft Lobe Lift – Exhaust Non AFM
6.97 mm
0.2741 in

•Camshaft Lobe Lift – Exhaust AFM
7.10 mm
0.279 in

•Camshaft Lobe Lift – Intake Non AFM
7.08 mm
0.278 in

•Camshaft Lobe Lift – Intake AFM
7.21 mm
0.283 in

-----------------------------------------

•Valve Lift – Exhaust Non AFM
12.500 mm
0.492 in

•Valve Lift – Exhaust
12.753 mm
0.502 in

•Valve Lift – Intake Non AFM
12.700 mm
0.499 in

•Valve Lift – Intake
12.953 mm
0.509 in

•Rocker Arms – Valve Rocker Arm Ratio
1.80:1