360 timing advance problems
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Projectile Dart
Well-Known Member
sounds like you're connecting to manifold vacuum instead of ported vacuum
gross oversimplification but... manifold vacuum has full vacuum at idle but loses vacuum when you step on the throttle
ported vacuum does the opposite where you have no vacuum at idle and you gain vacuum by moving the throttle
when you're connecting the vacuum advance to manifold, you are immediately gaining full vacuum advance at idle which could be adding up to 15* instantly.. then when you start driving and you want the vacuum advance to kick in, it's doing the opposite and dropping off
some people tune their cars (with big cams) to run this way but you have to know what you're doing and have the correct advanced initial timing to make it run well
gross oversimplification but... manifold vacuum has full vacuum at idle but loses vacuum when you step on the throttle
ported vacuum does the opposite where you have no vacuum at idle and you gain vacuum by moving the throttle
when you're connecting the vacuum advance to manifold, you are immediately gaining full vacuum advance at idle which could be adding up to 15* instantly.. then when you start driving and you want the vacuum advance to kick in, it's doing the opposite and dropping off
some people tune their cars (with big cams) to run this way but you have to know what you're doing and have the correct advanced initial timing to make it run well
Projectile Dart
Well-Known Member
what carb do you have?
or send a pic of your set up?
or send a pic of your set up?
Projectile Dart
Well-Known Member
the edelbrock should have 3 vacuum ports on the front of it. One large one in the middle by the idle mixture screws, and 1 on either side of it. The left port (passenger side) will be ported vacuum, the right port (driver side) is manifold vacuum and is what I am assuming you are hooked up to. If my assumption is correct then move the vacuum line from the right side to the left side and make sure to plug any open ports.
Projectile Dart
Well-Known Member
pic
67Dart273
Well-Known Member
Actually you "can" (notice " "!!) connect to manifold vacuum, but the factory was to ported. Some people INSIST that manifold vacuum is "better" but to do so you must have the mechanical advance set up accordingly, and obviously set initial timing accordingly.
I am a ported man, all the way, LOLOL
I am a ported man, all the way, LOLOL
hotrod swinger
Well-Known Member
Ported all the way, and it’s also possible your vacuum can is either leaking or needs to be adjusted.
If the vacuum advance hose or the vacuum advance itself is not holding vacuum your engine would run ruff due to vacuum leak.
If the vacuum advance hose or the vacuum advance itself is not holding vacuum your engine would run ruff due to vacuum leak.
[1] If connected to pass side, it is PORTED [ PVA ].
[2] This post is another great example of ignorance getting in the way of FACTS; blaming MVA when it is not to blame: because we know NOTHING about the numbers: was it in fact connected to MVA? Where was the initial timing set? If it was set to 20*, MVA might do little if anything on a mild engine. How much did VA add? Some cans can add 30*. Etc.
[3] If in fact it was connected to PVA, then there is a tuning problem because there should be vacuum on the PVA port at idle. Cause of THAT problem needs to be addressed first.
MVA works PERFECTLY as advertised when it is set up correctly, period.
[2] This post is another great example of ignorance getting in the way of FACTS; blaming MVA when it is not to blame: because we know NOTHING about the numbers: was it in fact connected to MVA? Where was the initial timing set? If it was set to 20*, MVA might do little if anything on a mild engine. How much did VA add? Some cans can add 30*. Etc.
[3] If in fact it was connected to PVA, then there is a tuning problem because there should be vacuum on the PVA port at idle. Cause of THAT problem needs to be addressed first.
MVA works PERFECTLY as advertised when it is set up correctly, period.
hotrod swinger
Well-Known Member
Lol, the passion!
DARTLARRY
Well-Known Member
What is your initial timing? Sometimes if the initial is too high, when the vacuum comes in it will ping. I had the same problem, and had to lower the initial timing. I know all set ups are different, but I run 12deg. initial, 34 deg. total, and all in with vacuum advance is around 45 deg.
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^^^This^^^
The key piece of information missing so far is the knowing what distributor you have.
And even with knowing the distributor, the advance curve often isn't what you think it is, or what the manufacturer says it is. Best to measure timing vs. rpm from the slowest rpm you can get it to run at, then every 200 or 250 rpm as high as you and your tach are willing to go.
Getting the timing to match the compression, chamber efficiency, cam, and rpm under load is the most important thing.*
Factory initial on most 360s was tweaked to reduce various emissions. They made up this with a quick advance above idle rpm. If stuck with one of those distributors or one like it, sometimes using manifold vacuum on the vacuum pod is a simple workaround. it has to be fairly stable. If the manfold vac us bouncing around then the vac adv and rpm will be bouncing aorund.
A better fix is what Rockable did here later in thread.
*Chrysler on what timing does.
DARTLARRY
Well-Known Member
If you set full mechanical advance to between 32 and 36 degrees at around, or above 3,00 rpm. After setting this, your initial timing will probably fall in the 8 to 12 degrees advanced range. To do this you will need to unhook, and plug the vacuum advance line. Doing this will establish a good starting point to work from.
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evan shealy
New Member
I ran into the same issue on my D150 today. Replaced the pick up coil, set timing and when I reconnected the vacuum advance, bam. choked down. Ran across this discussion and didn't find any answers here so I thought I would add what I found.
When I replaced the pickup coil I didn't get the reluctor wheel correctly seated on the distributor shaft. The roll pin wasn't in the slot. So yeah, I could get it timed but it really wasn't in time. After getting the reluctor properly seated on the distributor shaft, and re-adjusting the timing, the vacuum advance works like it should now.
So if you have been into the distributor or had it rebuilt, check to make shure the reluctor is seated properly and make sure the roll pin is in the correct slot on the wheel. The slot between the slashes is for small blocks, the other is for big blocks.
When I replaced the pickup coil I didn't get the reluctor wheel correctly seated on the distributor shaft. The roll pin wasn't in the slot. So yeah, I could get it timed but it really wasn't in time. After getting the reluctor properly seated on the distributor shaft, and re-adjusting the timing, the vacuum advance works like it should now.
So if you have been into the distributor or had it rebuilt, check to make shure the reluctor is seated properly and make sure the roll pin is in the correct slot on the wheel. The slot between the slashes is for small blocks, the other is for big blocks.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Your mild 360, will like idle timing as high as 25 or more degrees.
The Vcan is not likely to pull more than ~14/16 at the most and only with a high intake vacuum. But suppose it does at whatever idle vacuum you have.
Suppose you set the mechanical timing to 10*. Hooked to Full manifold Vacuum, that would be a total of say 25* which is NOT too much to idle on. But if you set your idle-timing to 20*, now you could be pushing 35*, and there is a very good chance that your mild 360 would complain about that as you tip the throttle in.
Here's the thing; when cruising the hiway, your mild 360 might like 56* of cruise timing. With just 15 in the Vcan you would need 41* in the mechanical plus idle. You could do it with say 25 in the mechanical and 16 on the idle. But your mild open-chamber iron-headed "monster" is sure to detonate itself to pieces when you nail the gas.
All numbers are hypothetical.
And the other thing is this;
Most or a lot of guys will just adjust the distributor to hit 36* at 3600 rpm or thereabouts, and let the idle-timing be whatever it will be, as long as the engine has enough power to idle on whatever it thus gets. By the time the engine ramps up to stall rpm, the Vacuum advance should have dropped out, and the total power-timing could be ~24*, or perhaps a lil more. While maybe not ideal, it ain't that shabby for a mild 360; and at least the pistons won't rattle their skirts off.
Could you do better? Probably.
Should you do better? If you are careful and take your time sneaking up on it, sure. But again; 3* not enough power-timing might be 7hp over the nose. But if to get that 3*, the engine detonates below say 3400, then that would be a bad idea; DON"T go there. Your azz-dyno will never notice 7hp in your 360 on the street.
Happy HotRodding
The Vcan is not likely to pull more than ~14/16 at the most and only with a high intake vacuum. But suppose it does at whatever idle vacuum you have.
Suppose you set the mechanical timing to 10*. Hooked to Full manifold Vacuum, that would be a total of say 25* which is NOT too much to idle on. But if you set your idle-timing to 20*, now you could be pushing 35*, and there is a very good chance that your mild 360 would complain about that as you tip the throttle in.
Here's the thing; when cruising the hiway, your mild 360 might like 56* of cruise timing. With just 15 in the Vcan you would need 41* in the mechanical plus idle. You could do it with say 25 in the mechanical and 16 on the idle. But your mild open-chamber iron-headed "monster" is sure to detonate itself to pieces when you nail the gas.
All numbers are hypothetical.
And the other thing is this;
Most or a lot of guys will just adjust the distributor to hit 36* at 3600 rpm or thereabouts, and let the idle-timing be whatever it will be, as long as the engine has enough power to idle on whatever it thus gets. By the time the engine ramps up to stall rpm, the Vacuum advance should have dropped out, and the total power-timing could be ~24*, or perhaps a lil more. While maybe not ideal, it ain't that shabby for a mild 360; and at least the pistons won't rattle their skirts off.
Could you do better? Probably.
Should you do better? If you are careful and take your time sneaking up on it, sure. But again; 3* not enough power-timing might be 7hp over the nose. But if to get that 3*, the engine detonates below say 3400, then that would be a bad idea; DON"T go there. Your azz-dyno will never notice 7hp in your 360 on the street.
Happy HotRodding
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