Stock Distributor Re-Curve

[68 4spd Fury]

Don't know what you have, but mine had a "Distributor vacuum control valve", I member back when these hit the trash pretty quick. My car ran good when I got it so didn't worry about it. Until recently, was doing some adjustments and what sounded like an exhaust leak was this thing rattling around. Disconnected it and ran even better.

 

[CBODY67]

Thanks CBODY67! Will check those manifold bolts and I've never used octane booster. Only full tanks of 94 octane all summer and only started pinging after driving for 30 minutes or more (guess that's the warm up time). I read this on Thursday: http://moparconnectionmagazine.com/gallery-distributor-recurving-for-improved-fuel-economy/. Also I know you said base timing comes in at 1000 rpm but according to my service manual it says for the stock distributor, timing starts coming in at 450 rpm.

The guys in the website link I added were experiencing the same part throttle detonation like me. Sadly, they fail to state the octane rating of the fuel. They also fail to say if they're using ported or manifold vacuum to run the distributor. Anyways, they say "The advance was too abundant, and there was a persistent light-throttle rattle (detonation) at about 17” of vacuum." Their overall solution was to get rid of the "engine's 1970's emissions laden" components, delay the mechanical advance until 1750 rpm (up from 700 rpm) and reduce the vacuum advance rate using an allen wrench.

Before mods, they had 0* initial (for emissions) and 33* mechanical coming in at 700 up to 4000. After they had 15* initial and 18* mechanical coming in at 1750 up to 3000.

They state an average increase of 26% in fuel economy (16mpg compared to 21mpg) and an increase in horsepower of 15-20% all over the rpm range.

For my car I should stiffen up the springs to make it come in later, reduce travel in the slots to no go too high too soon and do something with the vacuum can to get my economy. I'm averaging between 9 and 10 mpg with my ported setup.

I'll let you know if I find a screw in my vac can.

In prior times, there were several orientations toward "better" advance curves in distributors. It sounds like they are using some of them. Basically, they'd either delete the vacuum advance altogether or lessen its affect (shorter slots and such). This gave them an allegedly desired more consistent advance curve, which was mostly mechanical. In some cases, this orientation worked pretty good. But was mostly "hot rod" in nature, by observation. Any benefits mentioned might well have happened in a driving environment different from yours, which can affect fuel economy. From looking at other Chrysler 383/400/440 distributor specs, the '66 and '67 383 2bbl specs are pretty decent. When initial timing was retarded, with the mechanical advance being slower, initially, after 2500rpm, it was all back to normal, usually. The IM240 emissions driving test had a max road speed of 55mph, so that's all the emissions calibrations needed to address, it was claimed.

I presume y'all put the spark plugs back to Champion J-14Y, or equivalent? You might try going down to J-12Y, or equivalent. The '72 spec for the 400 2bbl was J-13Y, with the 4bbl plug being colder.

IF the carb is in a lean spot, try manually downshifting to "2" with the same throttle setting. Does the clatter change or diminish? In "D", can you accel out of the clatter range, or does it continue and get worse?

Seek out a speed shop or tune-up shop that has a chassis dyno. In their "road load simulation" mode, see if the clatter changes AND check the air/fuel ratio at that time. When the old local dealership did their tune-ups, they'd routinely use the Sunn Air Fuel Ratio meter to check carb function and when setting the idle speed. With the rpm at about 2500, the a/f would typically be 14.7 to 1, which is ideal. Once, I asked about a learner idle ratio. They easily got it to 14.2, which was what the later emissions setting were listed as. But for a smoother idle, I think it ended up at about 13.5.

My orientation is that things should work pretty good with the stock settings, base timing, etc. Because they apparently don't might indicate something's been messed with, somewhere down the line.

CBODY67

The fact that you mention a 30 minute time of operation before your pinging starts could well indicate a piece of carbon in a combustion chamber that finally "got hot" and is causing issues. Worst case scenario is to remove the heads and clean them with a wire brush on the end of a drill motor.

 

[CBODY67]

Don't know what you have, but mine had a "Distributor vacuum control valve", I member back when these hit the trash pretty quick. My car ran good when I got it so didn't worry about it. Until recently, was doing some adjustments and what sounded like an exhaust leak was this thing rattling around. Disconnected it and ran even better.View attachment 218628

Looks like some sort of emissions control device from back then? Mainly on CA or CA-spec vehicles? Or on manual trans vehicles?

CBODY67

 

[Nicholas Gromak]

Don't know what you have, but mine had a "Distributor vacuum control valve", I member back when these hit the trash pretty quick. My car ran good when I got it so didn't worry about it. Until recently, was doing some adjustments and what sounded like an exhaust leak was this thing rattling around. Disconnected it and ran even better.View attachment 218628

That looks to be part of the Cleaner Air Package, which mine does not have. According to specs they have timing retarded to top dead center to increase the after burning of air pollutants to meet California state emissions.

 

[Nicholas Gromak]

IF the carb is in a lean spot, try manually downshifting to "2" with the same throttle setting. Does the clatter change or diminish? In "D", can you accel out of the clatter range, or does it continue and get worse?

I can accel out of it if I manage to reach the power valve.

I presume y'all put the spark plugs back to Champion J-14Y, or equivalent?

Yup. I got to see the boxes and read the writing when my mechanic put them in.

I also checked those bolts and they're on good. The heat valve on the passenger side of the engine makes a little clacking noise at part throttle as it bobs up and down but I don't think this is what I'm hearing. It sounds too light. The pinging i'm hearing is really a knock not a tick tick tick. I could try zip tying it open and listening for the sound. Drove the car for 20 minutes today to the store with factory settings set, on 87 octane with no problems. Will try the downshift thing on my way to work if I hear it.

Next summer I'll drill the exhaust and install a wideband O2 meter.

 

[Nicholas Gromak]

Here is my engine:

 

[70bigblockdodge]

If your regular 383 is pinging (detonating) on "good gas" you have something wrong. Your car should run and drive very well with no vacuum advance. The vacuum advance is there specifically for fuel mileage, lite it early for a more complete burn at low cylinder fill/high vacuum.
I'm going to take two wild guesses but may have some merit.
Your combustion chambers are carboned up creating hot spots helping to cause detonation.
Your vacuum advance canister is adjusted too weak making it be very advanced at very little vacuum, this will make the advance be at max until down to very low vacuum.

 

[Nicholas Gromak]

If your regular 383 is pinging (detonating) on "good gas" you have something wrong. Your car should run and drive very well with no vacuum advance. The vacuum advance is there specifically for fuel mileage, lite it early for a more complete burn at low cylinder fill/high vacuum.
I'm going to take two wild guesses but may have some merit.
Your combustion chambers are carboned up creating hot spots helping to cause detonation.
Your vacuum advance canister is adjusted too weak making it be very advanced at very little vacuum, this will make the advance be at max until down to very low vacuum.

I have a scope that I can stick down the plug holes to check for carbon but no socket for removing the plugs. I'll pick one up on Tuesday and have a look. I still haven't checked the vacuum can to see if it has an adjustment. Will do that tomorrow.

Thanks!

 

[70bigblockdodge]

3/32 Allen wrench in through the nipple

 

[CBODY67]

In addition to the spark plug socket, a u-joint, a 4" socket extension, maybe a 6" extension, too, along with a short Phillips head screwdriver to remove the gravel shield on the steering coupling (to get to #7 plug, if the shield is there) . . . if you don't already have them.

For many plugs, using the u-joint as an extension works pretty well, as the plugs are recessed from the outer edge of their heat shields.

There is a YouTube channel for a younger guy that uses a borescope to check the effectiveness of popular de-carbon additives. Before and after, so you'll know what you're looking at.

CBODY67

 

[Gerald Morris]

I tried manifold vacuum w the distributor I'm now happily running w a decently rebuilt Stromberg WWC on the proper port. Stick with the ported vacuum friend. CBody 67 helped ME just a couple weeks ago with a pinging issue on MY 66 2 bbl Newport. I finally found a sweet spot in my timing at about 14 degrees BTDC with the new Cardone 843817 I bought when the reman 303817 I had run for a bit over a year was found to have an utterly defective vac advance. I twiddled and diddled a couple months before hitting this spot after a fresh re-read of the FSM. When time and money permit, I would love to rebuild the 30-3817 w a good vac advance IFF I can FIND one for it that doesn't cost more than another new distributor.

I'm running Shell 91 octane now which is about the best pump petrol I can find down here. Mathilda purrs pretty sweetly with it and I have NO PINGS, not even the slightest chatter when accelerating now. Even the kickdown is working smartly. Heed Mr. CBODY67 bro. He'll steer you down the right road.

 

[halifaxhops]

Thanks for the reply halifaxhops!

Here's what I got: 383 big block 9.2/1 Compression. 2bbl Stromberg WWC3 carb. Stock iron heads. Stock points distributor (see picture for timing and part number). Stock cam, Stock cast (single dual plane???) intake, Stock cast exhaust manifolds, Single exhaust pipe 1.5" diameter. Also this spring, I had my mechanic replace spark plugs, plug wires, new set of contacts, new coil, new condenser, set the dwell and all that.

From the manual it looks like I was into the mechanical while taking my measurements, oops. Just throwing some numbers here lets say we have 2 engines both set at 12.5* initial like the manual. Both are lightly accelerating up a hill in 3rd. I've got traffic behind me so I've got to speed up. For simplicity's sake lets say the 2 engines start at the same rpm say 2150. According to the manual, 2150rpm would bring mechanical to about 12.5* ontop of initial = 25*. From driving around with the gauge hooked to manifold I know that light acceleration, the vacuum is 10". For ported it might be higher say 15" due to the high load. According to the manual at 10" the vacuum should be around 8* and at 15" it's maxed at 13.5*

The manifold vacuum engine starts at 12.5+12.5+8= 33* but he still has to speed up to get away from traffic. The accelerator is pressed enriching the air fuel mix, manifold vacuum drops to below 5" (from tests), and the timing is retarded from 33 to 12.5+12.5+0= 25* and away he goes preventing detonation as he does.

The ported vacuum engine also starts at 33* but speeding up does nothing except go higher. All the settings are maxed out. "The rich air fuel mix burns faster" or so people say, and coupled with the high degree of timing, ping ping ping all the way home.

My problem with the ported vacuum setup is not only does it ping on hills but it also pings after every gear shift when the engine is suddenly loaded. Also from stop signs.

View attachment 218497

When you say the initial is set at 12.5 is that BTDC? If it is advanced that can be the whole issue, That distributor is adding almost 60 degrees at the crank if it is working properly.

 

[68 4spd Fury]

Looks like some sort of emissions control device from back then? Mainly on CA or CA-spec vehicles? Or on manual trans vehicles?

CBODY67

It has the "Chrysler Cleaner air package" car was sold new in Wisconsin so probably not CA emissions. Don't know if it was exclusive to manual trans cars or not.

 

[68 4spd Fury]

Here is my engine:
View attachment 218648 View attachment 218649 View attachment 218650 View attachment 218651 View attachment 218652

That's clean.

 

[68 4spd Fury]

That looks to be part of the Cleaner Air Package, which mine does not have. According to specs they have timing retarded to top dead center to increase the after burning of air pollutants to meet California state emissions.

Sticker in engine compartment.

 

[Nicholas Gromak]

Sticker in engine compartment.
View attachment 219070

That's clean too.

No allen screw in the vacuum canister. Pulled the spark plugs out of the passenger side of engine (2-4-6-8 i think) and checked for carbon buildup on the pistons. Nothing too bad but some is beginning to flake off creating a white edge wherever the heat is highest. Maybe this could be creating hot spots.

Went for a night cruise and about 1 hour in I started having problems. Stopped and pulled & plugged the vac line from the distributor and no problems all the way home.

Plugs were half white (because they're new) and tan colored on the other which would indicate a lean running condition.

Cylinders still have the factory hone. Can see the reflection in all of them.

 

[1970cat]

tan is good. why were the other plugs replaced?

 

[70bigblockdodge]

Have you ever cleaned the fuel system? Sounds to me as if you have lean conditions and getting leaner as car runs like dirty pick up sock and or fuel filter or possible clogged fuel line. Another possibility is the pick up in the tank may have pin holes in it due to rust and is sucking small amounts of air and filling filter with air then makes the car go lean after some time.
Just some thoughts.
I really cannot see how your getting that much loss from detonation without something completely wrong.
You need to look in other areas, your low compression engine should not be having any problems with premium gasoline.

 

[halifaxhops]

so with less advance no problem, so it is set after top dead center then? Really sounds like to much advance.

 

[70bigblockdodge]

so with less advance no problem, so it is set after top dead center then? Really sounds like to much advance.

I agree with what your saying. He has either another problem or is way out of time that a low compression engine like that can't run on good gas.
But my 400 and 440 are measured mid 8:1 engines and run fine on 89 octane with 36° total, plus vacuum at cruise.
Besides the fact that he list the car runs worse after an hour.
1. Your timing does not change after a hour of driving (or there is something wrong if it does)
2. It's a machine and does not recognize time, if it has fuel, air ,and spark it runs forever.
3. I can understand wanting to make it get better MPG, but I'm not sure the rest of the engine is correct.
I'm out, with the guessing game.