Need experienced opinion - Can vacuum advance cause pinging?

[Newkidonthebloc]

Another old goat speaking from personal experience here - no expertise claimed by me. Seriously.
Ok...
- Speaking stock for stock, I've always found the 383 wants a little less timing than its' 440 big brother -
in any mode. At idle, a bone stock 440 likes at least 10BTDC; the 383, a little less, but more than
5BTDC every time I had one in front of me. 7-8 seemed to work usually.
- The stocker 383 seemed to like an "all in" setting in the low 30's BTDC (with vacuum advance plugged
off, of course) while the 440 always seemed to like a little more, like 35-36BTDC.

(This is the way I typically set timing on these engines - at about 2400RPM, I go for the best direct vacuum
reading and the smoothest running, which determines the "all in" setting - and whatever that leaves the
idle timing at as a result is typically acceptable, too. The engine will tell you where it's happiest!).

(Either engine will happily motor on down the road with the vacuum advance disconnected, by the way.
You'll suffer some fuel economy and maybe even a little cooling from doing it, but it's fine otherwise).

Yes, many of the Chrysler factory distributors have adjustable vacuum advances on them (the electronic
ones especially) and a simple little hex wrench (I'm thinking 3/32" ??) is all that is needed.
Once you get your base timing figured out, then you can start experimenting with the vacuum advance -
but know that sometimes without some modifications, that rascal will never "settle down" to an acceptable
operating state - the engine will be "jittery" at cruise speeds and will "rattle" upon letting up on the throttle
to coast/slow down.
Yes, that's what you're hearing if you hear it at that point - it's pre-ignition where it's not welcome by the
engine. It most likely is caused by the vacuum advance but as others have said, it can also be caused by
an overly lean condition, too - and if the engine is running hot, well, that just makes the whole mess worse!

Today's crap gas, along with whatever modifications have been made to the engine, how old it is,
what it's sitting in, all sorts of factors lead to detonation and pre-ignition.
In my own '68 GTX with a "semi-warmed" 440, I run the Mopar electronic ignition sans vacuum advance
as a result. The car is happy (but a gas hog, admittedly) and there's no staccato music under the hood.

Thank you for your reply! This weekend I will check the timing once more and set it to 7 at idle and low 30s at high RPM. I do think the car runs fine with the current setting but I will change it and see whether it helped or not.

 

[Newkidonthebloc]

Yes factory distributors had the adjustable cans with hex, not sure when they started that, most of the 20 or so I have are that way. Stock initial timing on a 383 2bbl automatic was 7.5 degrees before if I recall right 0 degrees for a 4 speed. It depends what distributor he has. My 68 440 auto distributor does not have the adjustable can.

Unfortunately I do not have a factory distributor. The car came with a MSD ready-to-run distributor. Those do not have adjustable vacuum cans but I do have a set of springs and bushings that allows me to change the curve of the mechanical timing.

 

[Hemirunner]

No offense, but I do know what that all means. I hoped that my description of my problem would let you know that I know what I am talking about but am a complete newb in actually physically applying the knowledge to setting the correct timing and tuning. I have read about it for many years and know a fair bit but I never had a car to apply that on. I lack experience and therefore am not quite sure whether the sound I am hearing is normal or not.
I also have a kit means to change the curve of the distributor which is probably the next thing I will do once I figure out what causes the sound and whether it actually is detonation.

Having that understanding really helps in your case. From your description, the timing seems to be the likely issue. Recurving the distributor is going to be a must in your case. What that curve looks like has been the subject of lots of debate. Good luck and report back.

 

[Newkidonthebloc]

How are things over there? Hearing some interesting stories about your wonderful farmers.
Second largest food producer in the world, that's amazing!

Yeah it is a crazy protest that has been going on for days now. I do respect the farmers and find it amazing what they can produce in such a small country with a relatively bad climate. However, in some regions there is simply too much agriculture going on (big stalls with loads of animals close to neighbouring towns). The story obviously has two sides to it but our politicians always trying to compromise while being misinformed created a big **** show.

 

[Newkidonthebloc]

Your vacuum advance canister (where the hose plugs into the distributor) should be adjustable.
You can put a small allen wrench through the port where the hose connects and try going counter clockwise on the spring setting.
This changes makes the advance mechanism requre more vacuum.
Count your turns so you can always go back.
For some light reading:

How To Limit and Adjust Chrysler Vacuum Advance Cans

Unfortunately I do not have the stock distributor. The car came with a MSD distributor which do not have adjustable vacuum cans. I do have the ability to recurve the mechanical timing though.

 

[Newkidonthebloc]

High mileage, might have a bit of carbon build up in the cylinders/heads. Pull some spark plugs to see what they look like.

I have posted about the plugs a while back. They look pretty good! I am just making sure that the timing is correct.

 

[Newkidonthebloc]

My 67 Satellite 383 4bbl / 727 / 3.23SG would ping under light throttle cruising in 3000 rpm range when I first got it with about 95k miles on it. It would go away under acceleration with enough gas. Running it on 93 octane Premium helped. Retarding the timing a few degrees also helped. I also played around with octane boosters - they worked, but were economical for everday driving at the time. Rebuilding the engine with slightly lower CR and a different cam cured it completely.

EDIT: not economical

I do always run premium 98 octane. I also believe that the 2bbl 383 had a CR of 9.2 from the factory which by now is probably even lower. I also do not hear any pinging during driving it, just when coasting/cruising at low RPM where I do not expect pinging. (and again, I have never really heard pinging so I am suspecting it to be pinging but am not sure)

 

[Ron H]

As I follow, you have described a tired motor and identified timing chain slop. This is a high hurdle for gaining perfection with timing. Another thing if you haven’t done this, check the carb adjustment to have that out of the mix with your tuning efforts.

 

[Newkidonthebloc]

It (vacuum advance) can contribute to pinging but usually when cruising at high speed at steady throttle (vacuum high and engine speed high enough to bring in most mech advance). Kind of doubt that is what you are experiencing unless someone has put real, real light advance springs in your distributor so that it fully advances by 30 - 40 mph. Try plugging the vacuum advance line and see if it quits. Could be some valve train noise but just a wild guess.

I did try that and the sound almost went away at 30 mph (or in other words became much less noticable). However, at idle and pulling away the car did perform much worse.

 

[Newkidonthebloc]

As I follow, you have described a tired motor and identified timing chain slop. This is a high hurdle for gaining perfection with timing. Another thing if you haven’t done this, check the carb adjustment to have that out of the mix with your tuning efforts.

Yeah this weekend I am going to retard the timing a few degrees and retune the carb for the new setting with a vacuum gauge. I will let you know what comes out of this. I want to take the car on a holiday and therefore I wanted to be entirely sure that I do not ruin the engine with bad timing settings. I do agree that the engine is tired. I plan on freshening it up next winter.

 

[moparedtn]

Thank you for your reply! This weekend I will check the timing once more and set it to 7 at idle and low 30s at high RPM. I do think the car runs fine with the current setting but I will change it and see whether it helped or not.

Hook up a vacuum gauge to a direct vacuum port so you can see what you think the engine is telling you.
It will pretty much confirm or steer your adjustments.

 

[moparedtn]

As I follow, you have described a tired motor and identified timing chain slop. This is a high hurdle for gaining perfection with timing. Another thing if you haven’t done this, check the carb adjustment to have that out of the mix with your tuning efforts.

Agree! The vacuum gauge works wonders for adjusting the carb as well.

 

[Dragon Slayer]

So do you know the max mechanical timing added by the MSD distributor. You have clarified a lot of info, but many stock mopar distributor 68 and up (emissions) had mechanical advance from 15 to 17 at distributor which is 30 to 34 degrees at crank. They ran very little initial, usually 0. And a few models retarded. So if you add initial and do not limit mechanical you can be well above the total folks mention. Like 40 to 45 total and that is without vacuum.
Also, you did not see full mechanical unit about 4400 rpm. So your measurements at 3000 rpm would not be total, unless you know the spring rate was change and it is all in early.

Lastly, the vacuum can should have an arm stamp for total vacuum added. Lets say a stamp of 10. That is 20 degree added timing at high vacuum.

So I think your hearing folks talk about stock values and other of performance values (assuming they control all the variables). No one can really tell you the right initial to use without knowing the mechanical built in the distributor.

 

[QOTHL]

I lack experience and therefore am not quite sure whether the sound I am hearing is normal or not.

I've been to automotive school and have learned a lot from the members of this forum but am far from experienced. It is hard to diagnose something long distance. My first reaction to your description was that this is a sound that a big block makes when you take your foot off the gas especially, and conceivably at low revs like cruising. If you're not real familiar with big block muscle cars, you could easily mistake a lot of sounds as being a problem when that is just the nature of THE BEAST.
When I hear preignition knock, it's usually when I'm accelerating, not decelerating or cruising.
Checking timing: you can find almost anything like that on YouTube. I have done a lot of stuff for the first time from watching videos there.
The first time I drove a Barracuda I thought there's something wrong with this car. I was used to driving 69 Chargers which is like night and day. I happened to see a video from Jay Leno's Garage where his guest was Richard Carpenter who has an original 1970 'Cuda 440 Six Pack. They took it for a drive and a comment was made about how it "rides like a buckboard" but is a blast to drive. It's just the way the car is built. My 440 six pack 4 speed sounds awesome but doesn't sound like my other 440's, it kind of sounds like a truck...very throaty, real mean.
I. have seen the movie Vanishing Point many times which features an E body 4 speed. Someone on here may say the engine sounds were not the actual ones from the car in the movie but it sure sounds a lot like my 4 speed 'Cuda!
Just my 2¢. I still say go out and FLOOR IT! Get that nasty carbon out of there so it can help plants grow!

 

[4406bbl]

Don't be flooring it a bunch until you are sure you are at 38 degrees total or less. I would start with the 7 degrees initial, 28 mechanical, and set the advance springs so all timing is in and solid, not bouncing around at about 200 rpm below your hiway cruise rpm. I agree with others with mechanical coming in so late the vacuum advance may be getting you above 50 degrees total at light throttle. You say it runs good with 10 degrees, I don't see that changing much, and you are still in the safe zone with 28 and 10. When you hook up vacuum advance after this it may rattle, and need limiting, there has to be a way to do it with wire, metal or a screw.

 

[GMP440]

To Geoff, lets keep these responses positive without talking down to others. I was referring to base timing not total timing. Just wanted to clairify that.

 

[Geoff 2]

GMP440,

Not talking down to you....or anybody else. I know exactly what you meant, you stated it clearly but it was incorrect, period. I corrected it, but then you stated the wrong info again. The poor guy who started the thread is probably as confused as ever with misleading info.

 

[GMP440]

GMP440,

Not talking down to you....or anybody else. I know exactly what you meant, you stated it clearly but it was incorrect, period. I corrected it, but then you stated the wrong info again. The poor guy who started the thread is probably as confused as ever with misleading info.

Whatever. I stand by what I stated. Lets just leave it at that and move on.

 

[oldbee]

Trickle some water down the carb,while revving it up(carbon buildup?) ; don’t drown out the engine. Hydraulic buildup is nasty!!

 

[Geoff 2]

New kid,
Going to be very hard to fix via the internet with your limited knowledge of ign. Primary cause of pinging [ detonation ] is caused by heat &/or load. No load in neutral, & it doesn't ping, right? Reducing H & L will help. A tired old engine makes it worse & who knows what internal changes have been made over 50 + yrs??
Retarding ign timing under load will fix it. Retarding ign timing will also kill performance & throttle response. Avoid at all cost if possible. So you could try the other parameter, heat. After fitting headers, the mixture is often lean & needs to be richened slightly. Lean mixtures cause overheating.
Initial timing of 10*. Try increasing it to 12-15*!! Yes, more not less. Millions of GM cars left showrooms idling with over 20* of timing at idle. This was accomplished by using vac adv connected to manifold vacuum [ Ch used the useless ported vac adv, PVA ]. The MVA added about 18-20* of timing at idle to the static amount to provide 20+*. What does this do? It makes the engine more efficient; it therefore does have not to work as hard & runs cooler. Remember, heat is the enemy. With the engine running cooler, at the instant you give it throttle, the cooler engine will be less likely to ping.
To run 15* initial, you will have to shorten the centri curve in the dist. A problem with most of the aftermarket dists like the MSD you have is that often have a quick performance curve that is the opposite of what you want when you have a pinging problem. I haven't used the Ch version of the MSD dist, but the black bush gives 18* of centri advance; that would give you 33* at WOT with 15* initial. A good starting point.
One final point. The initial timing quoted by the manufacturer is a compromise because they have to allow for the worst case scenario as to the car's use. Will it be towing a heavy trailer?
So there is some leeway in a situation like yours to deviate from factory settings.