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440 timing and pinging


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2:01 AM
Jun 5, 2023
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Newton, Wisconsin
Hi, I just joined and I hope its OK to pose a question on a C-Body, a 1970 Chrysler 300 convertible with 440 TNT (Magnum) and added 6-Pack. The question at this point is regarding timing. The car always pinged somewhat but its getting quite bad, even a low loads and RPM. I disconnected the vacuum advance which was connected to the carb port. This helped a little but is still bad.

Here is a breakdown of the car's setup. Most of this was done by the previous owner.

440 TNT 375HP
Rebuilt and bored .030 over
6-Pack - I have not tweaked the carbs for about 9 years now but just checked fuel levels and they are still good.
No choke plate or idle solenoid
Holley 5.5 Power valve
Holley 122-66 main jets
Edelbrock 5090 75cc E-Street aluminum heads
Comp Cam 21-306-4 Per Comp Cam - Great replacement for 440 6 pack and largest cam with stock converter.
Grind 270H
Intake and exhaust duration 270
Intake and exhaust duration at .050 lift 224
Intake and exhaust lift .470
Lobe separation 110
Exhaust Close ATDC: 21
Intake Open BTDC: 29
Exhaust Open BBDC: 69
Intake Close ABDC: 61
TTI Headers
MSD Streetfire CDI with Blaster 2 coil
Chrysler electronic distributor
Timing marks are accurate
Auto trans with stock converter
3.23 gears
Cold compression is 150 plus or minus a couple.

The car runs pretty nice with the exception of the pinging. It will turn off without run on and will hot start with just a touch of the key. Gets about 13 mpg on the highway. I do think its running a bit rich as I feel that I should have to blip the throttle more to keep it running at a cold start. The car will idle (slowly) on its own after a minute or two.

If I time it by “ear” and highest vacuum, its at 42 before at 900 rpm with 17 psi of vacuum. I could not get it to idle below 900 even with the idle speed screw completely backed out. I did not mess with any carb settings. My understanding is this may be normal depending on the camshaft.

Currently the timing is set at 12 before with an idle of 850 with the vacuum advance is disconnected and its pulling about 15.5 inches of vacuum. I’m using a ‘70s vintage Craftsman timing light with the spring coil that attaches directly to the plug. Not sure if the MDS is messing with this old timing light or not.

At 1500 rpm the timing already shows 32 before.
At 2000 rpm the timing increases to 38 before. I did not check it past 2000 rpm.

I’m thinking that the mechanical is coming in way too fast but I'm looking for your expertise. Should I try different springs or just bite the bullet and get the FireCore distributor.

Thank you all in “advance” for help a C-body guy out!

I'm predicting a fairly long thread.
One question will be, what pistons. What static compression ratio.
Did you try a different timing light.
[1] Do the heads/pistons provide quench? [ 0.060" or less between piston crown & head surface ] No quench makes it harder to control detonation.
[2] If you have quench, engine needs less WOT timing. Try 32-34*.
[3] You could also try stronger springs on the centri weights in the dist to delay timing advance.
[4] Heat & load. The enemy of det.
[5] A heavy car. Always going to be more prone to det under load.
[6] Try & use cold air induction & get the engine [ coolant ] running as cool as possible. You could try reducing the exh xover size, which heats the intake. I use a plate in the gasket & drill a 1/2-5/8" hole for some heat.
What type of plugs/heat range are you currently using?
The pistons are flat tops and based on my old notes, about .080" below at TDC.

I replaced the heads with the aluminum ones 9 years ago. According to Edelbrock, these heads were supposed to maintain stock compression. According to Summit's compression ratio calculator which used overbore and gasket thickness, it should be about 9.6:1 with the aluminum heads. That is when I changed the jets and power valve and the last time I tweaked the carbs.

The engine temp typically reads 180 degrees.

The plugs are Champion 711 as recommended by Edelbrock and gapped to .035. Should I have a larger gap with the MSD?

A 15-20% mix of 110 octane race gas to the normal 91 Shell (no ethanol) or adding BOOSTane to achieve a 97 octane rating does quiet things down but there is still some pinging at hard pulls. Since its a street ride I'd prefer not to have to take these measures.

I ran a borescope into #1 cylinder and there is some carbon build up on the piston. I'm trying some additives to get rid of that as I'm reluctant to run it hard with the pinging

Do you folks think that the readings I took are OK for this build? 32 at 1500 and 38 at 2000 without VA seem like a lot to me.
I would suggest checking the advance at higher RPM as well, why stop at 2000?
I agree that it's coming in quickly for a heavy car with original converter.
Check with @HALIFAXHOPS about heavier springs and you may need to limit the mechanical youre already at 26 degrees mechanical addition.
Short term back off the initial if you plan to drive it at all.
Predetonation is a killer.
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Sounds like it is coming in fast. You need a spring set to get it under control, I am out of them.
I can’t run my 68 year stock 440 at over 34 degrees timing w/o pinging (initial + centrifugal, vacuum advance plugged). But the aluminum heads should help some and probably tolerate a little more timing. IMO, the mechanical advance is coming in too quick especially with a large car. Peaking out at around 2800 to 3000 rpm would probably work better.

Edit: just remembered you mentioned an MSD ignition system. Try reducing the amount of mechanical advance a little and keep the initial timing the same. Get an MSD advance spring kit for some heavier advance springs.
A couple other points:

The car probably isn’t running rich on a cold start, but instead is lean. The role of a choke is to richen the engine up a little on a cold start to help it support combustion in a cold combustion temperature. Chokes are beneficial but if not installed, feathering the throttle for a minute or so to activate the accelerator pump and transition port fuel flow will work until it builds a little heat.

You probably should run a bit higher Hg power valve if your steady throttle and idle vacuum is around 15 - 16 Hg. Holley recommends dividing your highest vacuum reading by 2 to select a PV which would be a 7.5 or 8 with that vacuum. Not sure that’s going to make much difference in how the engine runs - it will kick in additional fuel slightly faster when you open the throttle.
What do the spark plugs look like?
Just in cast you are getting some oil in the combustion chamber?
To me, it sounds like you just need to limit your mechanical advance a little & “maybe” but ncrease initial timing slightly….and definitely take a hard look for minor vacuum leaks. Do you have any plugs that are “white” on the electrode?
I would double check timing with a newer dial-back timing light. The MSD might be messing with your old timing light?
Plugs look like car is idling quite a bit. I'd put new plugs in it and work on the tune. It does sound like the timing is coming in too fast?
Maybe the ignition was curved for a high stall torque converter?
FBO has a nice limiter plate and spring kit.

Are you using original or reproduction carbs?
On the outter reproduction carbs, they have the phenolic floats with aluminum hanger arms, and they can bend if the fuel pressure is too high.
We were chasing the float level raising even after adjusting the float level (and running out of adjustment), Found the fuel pressure was fairly high.
The center carb with the brass float did not seem to have this issue.
For on the street, on pump gas, I like to see timing something like 16 deg at idle, 20 deg at 2k, 25 deg at 2.8k, all in at 32 deg at 3.4k, and then plug in the vac advance to manifold vac.
Sounds like it is coming in fast. You need a spring set to get it under control, I am out of them.
I've probably got some heavier springs.
PM me if youre interested and I'll look at what I've got.
Thank you all for your input. The carbs are original and the car does quite a bit of low RPM cruising through town and the pinging has prevented me from cleaning its pipes.

Since the general consensus is that the mechanical is coming into early and possibly too much, and the fact that I also needed cap, and rotor, I ordered up the Summit (Firecore) distributor to hopefully ease this phase of the tuning process.

I'll keep you posted. Thanks!
Dang - red Xed out again, probably by a finger scroller (T. Brashears)
had same motor same issue, went 4 steps higher on the center carb main jets. problem solved. timing 12 before at idle. 42 total at 2000 with vacuum advance. lean condition is what makes it ping
Yes I read all the posts and do my best to take an "average" to come up with a starting point. The new distributor is installed with one black and one silver spring. Set initial timing at 16 without VA using the old timing light (a new one is on the way) and the car is soooo much better already. Still a slight ping so I'll try backing off the intial a bit and may take a bit off the total mechanical. Then see how VA comes into play. I'll keep you posted.
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