I have a 360 LA from the 70s. It has been rebuilt with a Comp Xtreme energy (206/212 @ .050 .432/.444) cam and almost too high compression. It has about 170 to 180 psi cranking pressure. I have had this combo for about 13 years now and has ran fine with 12° initial and around 30 degrees total. Lately, like the last fill up it has been pinging something terrible. I thought, at first, that it was the MSD 6AL box as I have had one fail in the past. The MSD that failed was causing the timing to jump to an extreme advance and run and ping terrible. At that time I switched back to the factory module and it would run fine. I replaced the MSD box and it was back to normal. This time I switched back to the factory setup and still the same issue. I always have to run supreme fuel so I thought I had put regular in by mistake. I have done this in the past too, but I am able to put a couple of bottles of octane boost and remedy the problem. This time however it didn't help. I also thought maybe I just got some really crappy fuel and I needed to completely start over. So I ran it near empty and replaced it with supreme (I paid careful attention this time) and still the same result.

What am I missing, what could cause this terrible ping in just the span of a tank of fuel. Its bad enough you can barely drive 55 and even then if you hit a small hill it will start pinging and you will have to slow down to 45 or maybe less sometimes. Any help would be appreciated.

If you used the same gas station they might have filled their tank with the wrong fuel. Happens Back In high school I worked at a cut rate station and we got whatever the trucks had in them regular to premium shell to exon. Was sure to fill up when driver told use it was high octane. lol

If it's not the fuel could be advance going bad? Good luck.

see what your total is (now) & what RPM it maxes out at.

I need a better timing light but with my marks on the balancer it appears to be in the neighborhood of 30°. I'm not sure what RPM it is coming in at but I would guess that it is around 3000. I work with a fellow with a dial back timing light. I'll get it tomorrow and check to be sure, but the movement of the advance didn't look out of the ordinary, for what that's worth.

As for the fuel, I used a totally different gas station this time. I was thinking the same this as you.

If you confirm your ignition setting have not changed you might want to make sure your cooling system is full and functioning properly, low coolant level will allow the temperature of the heads and combustion chambers to rise and cause ping. Also a lean fuel mixture will contribute to pinging (vacuum leak or carb problem).

also check the harmonic balancer outer ring hasn't slipped around.

30 degrees advance on a high static compression ratio LA 360 “might be” slightly high unless your cam lowers the dynamic compression. Plain old carbon deposits in just one cylinder can cause the pinging.

If it is any help here is a full throttle run recording of a Magnum 5.9 V8 on 89 Octane (actually 89 antiknock index) gasoline. Magnum heads swirl and tumble the air more so they require less spark advance than at least some of the LA cylinder heads.

the information below came from a full throttle run on a 1995 Magnum 5.9V8 Ram pickup:
******
I have been playing around with the 'record' feature of the Actron ScanTool
with OBD-I Chrysler Cartridge on my 1995 5.9V8 auto with 3.21 differential
gears.

This records and stores 5 readings, 3 seconds apart, of what happened with the
PCM computer sensors before you hit the button, and an additional 10 readings
3 seconds apart afterwards

Here is what the ScanTool recorded on some runs at full throttle in 2nd gear
up a pretty steep hill { I guess about 4% grade)
Outside temperature was in the 70's and the barometric pressure was 29.6 inches Hg.

MPH....RPM....SparkAdv..Vacuum....O2 voltsDC

40......2804.......19..........0.9..........0.86
48......3175.......19..........1.1..........0.90
54......3485.......18..........1.2..........0.90
60......3787.......21..........1.5..........0.90
65......4093.......24..........1.6..........0.90
71......4471.......24..........1.7..........0.92
76......4785.......28..........1.7..........0.90
80......5040.......28..........1.8..........0.90

Comments:
(a) I can't explain why the degrees of advance went down from 19 to 18 around
3400 rpm, but it read the same on two runs. Notice this occurs near the engine
Torque peak, where cylinder pressures are highest.

(b) note that the NTK made O2 sensor stays fairly rich at 0.90 volts.
14.7 air/fuel mixture is at 0.40 to 0.50 volts, so that reading confirms rich mixture.
By design full throttle stock Magnum 5.9 V8 air to fuel is a very rich 11.8

1995 FSM says 5.2 and 5.9 V8 static compression ratio is 9.1
Later year 1998 Dodge advertising dropped 5.9 V8 SCR to 8.9
With the 13 cc dish pistons typically 0.050 in the hole “real world” static might be around 8.7

Thanks for the info. That is a good chart you have. I wonder if the dip from 19° to 18° is the knock sensor retarding the timing. Assuming that that year model the computer controls the retard and not the vacuum. I have been working a lot so I haven't had a chance to look at it any closer. It's also not my primary driver so I haven't been in a panic to fix it. I am borrowing a better timing light today so I will be able to get some better diagnostic info.

Look for a vacuum leak, cracked vacuum hoses, bad pcv valve etc. What do the plugs look like (assuming you do not have an O2 gauge installed)?

Start with the plugs. They will tell you many things. You can even post pics if you have questions.

Years ago I had a warm 413 that ran good. Then one day it just started pinging on me. this particular setup was finicky about the gasoline you fed it so I always filled it with quality super, usually Shell SU2000 93 octane. Other brand super would sometimes ping but not Shell. Or for that matter Diamond Shamrock 96 octane, but finding that was a rarity.

Anyway, the pinging started despite the fact I had quality gas init.

Pulled the plugs and found that the fancy platinum tip plugs I put in, Bosch brand, had a material defect in three of them. The porcelain around the center electrode was gone. It was there when I installed them. That would cause the electrode to get red hot and make the engine ping. New Champions and all was well.

When things work fine then suddenly act up you gotta ask, "what changed?"

X2, that's what I was trying to decipher

All good ideas and well appreciated. It may be a while before I get a chance to dig in, but I will look at all the things you all have suggested. Thanks.

If it has an EGR valve, make sure it is working (not clogged or ruptured). EGR lowers combustion temp in an effort to fight NOX & will reduce ping.

IMO, you need to start with plotting mechanical timing vs. rpm.
Then if using vacuum advance, measure or estimate the amount of additional advance the is added when cruising.
To do that you'll need a vacuum gage at minimum, and a mity vac makes it easier.

The reason you need to do this is to find the timing in the driving conditions being discussed.
High compression engine does a better job of keeping heat in the chamber and may not need as much lead.
The goal is always the same. Enough lead to for the maxium pressure through the most efficent crank angles.

like supercuda said read your plugs they can tell you a lot and go two or three ranges cooler like an rn9yc champion .
and check your advance springs in the distributor they can rust and break especially MSD and cause the same problems .

As others have said, check your plugs.

Story time regarding gas, with how quickly and easily gas goes bad nowadays, I'm always leery of using premium because it doesn't have a high turn over rate as regular does, so it sits at the station much longer before getting a fresh batch.

Back when my wagon was my DD, I always used mid grade or premium because of the 440. One day I HAD to use the cheap regular. My wagon didn't ping bad, just occasionally under full throttle or under load, so imagine my surprise when it didn't ping at all with the regular in it. I tried premium again, the ping came back. I only used regular from there forward. (not a 'built' 440, just an internally stock '77 440).

never seen a knock sensor on a Magnum engine.