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#3384767 - 05/30/14 10:07 AM Re: Pinging goes away after vacuum adv disc - why? [Re: wag123]
440Magnum Offline


Registered: 02/01/09
Posts: 6099
Loc: Texas
Originally Posted By: wag123

As far as the vacuum supply to the distributor, they have that right as well. Lacking an air pump, you should be running manifold vacuum to the distributor, not port vacuum. But, that is NOT the way that it came from the factory. Prior to the use of exhaust air pumps (which started appearing in 1967-1968), distributor advance vacuum was always taken from the manifold. After air pumps were used, distributor advance vacuum was almost always taken from the carburetor throttle vacuum port. The difference is that, with the vacuum advance taken from the manifold, you got about 1/2 of the full vacuum advance at idle. With the vacuum advance taken from the carburetor throttle port, you got ZERO vacuum advance at idle. This is strictly an emissions control thing!


That is simply not true, at least not for all manufacturers. Chrysler virtually NEVER used straight manifold vacuum. My old 1949 Plymouth flathead six used PORT vacuum (through a flared-fitting copper line, no less). All my 50s, 60s, and 70s Mopars used ported vacuum. My '68 Ford 302 (no air pump) used ported vacuum. The 74 Mercury I drove in college used ported vacuum (no air pump, but all the other emissions stuff).

As I pointed out in another post, a huge drawback to manifold vacuum as the source for the advance is that manifold vacuum is at its absolute max at idle- you get 100% advance at idle. But the *instant* you touch the accelerator pedal and crack the butterflies open, manifold vacuum falls off, the timing retards, and (depending on the cam and other factors) the engine will feel like its bogging very badly.

Ported vacuum is zero at idle. When you crack the butterflies open, the transfer slots and vacuum port are exposed to the manifold vacuum (which also drops as the butterflies open) and some (but not 100%) advance is applied, making the engine accelerate smoothly. As the engine speed builds to match the butterfly opening, the ported vacuum continues to increase until full vacuum advance is reached. Now if you step on the gas further, the vacuum will drop and timing will retard to prevent pinging, but since this is already happening at an engine speed well above idle, you don't get the "fall on your face" bog that happens with straight manifold vacuum when you're coming off-idle.
_________________________
'66 Dodge Polara & '69 Dodge Coronet R/T both 440/727
'08 Ram 1500 4.7/545RFE
'12 Challenger SRT8 392/6-speed
'99 Cherokee 4.0, '11 Grand Cherokee 3.6

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#3384818 - 05/30/14 11:33 AM Re: Pinging goes away after vacuum adv disc - why? [Re: 440Magnum]
wag123 Offline


Registered: 06/14/11
Posts: 490
Loc: Texas
I beg to differ 440. I have a LOT of experience in this area.
Ported verses manifold vacuum control of the vacuum distributor advance is a much discussed and widely misunderstood topic. From Lars Grimsrud... "Ported vacuum was used as an emissions control method to retard timing at idle (by eliminating vacuum advance) in order to reduce hydrocarbon emissions."
Just because the vacuum advance is plumbed to the carburetor does NOT mean that it is ported (throttle plate controlled) vacuum. In most cases, this is just a convenient place to put a DEDICATED manifold vacuum port (note in a couple of the attached articles that they tell you NOT to run a "T" in another manifold vacuum line to get your vacuum for the distributor).

To back up what I said, here are some articles...
http://www.460ford.com/forum/showthread.php?t=117504
http://w2ner.com/distributors.htm
http://www.camaros.org/pdf/timing101.pdf
http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf
http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/Vaacuum_Advance_Specs.pdf

There is a wealth of additional information on the internet about this topic.
I can attest to what they talk about in these articles from personal experience over the last 45 years. There is one thing mentioned in one of the articles that I disagree on, I have found that you should NOT have full vacuum advance at idle. This can cause problems like the OP is experiencing. Most vacuum diaphragms have enough of a response delay in them that they won't cause a idle fluctuation at small idle vacuum variations.
I can also tell everyone from personal experience that IMHO, on a carbureted street driven non-emissions-system-equipped high performance vehicle, you should ALL be using a vacuum advance distributor and you should ALL be using manifold vacuum to control it.


Edited by wag123 (05/30/14 11:46 AM)

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#3384840 - 05/30/14 12:02 PM Re: Pinging goes away after vacuum adv disc - why? [Re: wag123]
Volvohead Offline


Registered: 05/25/05
Posts: 3335
Loc: SE Pa
440 is correct here, at least as it applied to the 385 FoMoCo big block family of the 68-72 era.

As diagrammed in the first vacuum schematic in my earlier post, the early versions of this engine used a two-port temperature regulated valve to supply distributor advance. In normal position, the valve supplied port vacuum. When the engine temperature elevated above threshold, the valve switched to manifold vacuum, which elevated idle speed to aid cooling.

And that is exactly how the system was laid out on every 429 & 460 I dealt with during that period. Simple, and rarely failed.

It's port vacuum advance in normal operation. And it's not that complicated a subject on this particular engine family.

And it's not the cause of the OP's timing problem. Even if the installer hooked up the vacuum advance to manifold, you would know it as soon as you attempted to set initial timing.

If the initial timing is set correctly, this is a mechanical advance problem, and I am very confident of that.

The only other possible cause for erratic timing is an aftermarket electronic breaker unit that has gone haywire. When these electronic things first came out, I still preferred a good set of blue streaks, which were more accurate and dependable.

. . . I wouldn't have castrated this engine down to 8.5/1 to begin with, but that's another issue. They run fine at 10.5/1 stock on today's fuels.

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#3384848 - 05/30/14 12:08 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
Oldswagon Offline


Registered: 01/23/03
Posts: 761
Loc: ON
Most Ford's reduced ignition timing at idle by way of a dual diaphragm vacuum advance unit. The front part was connected to ported vacuum like most other vacuum advances. It has a rear diaphragm that connected to manifold vacuum. This system reduce the ignition advance at idle and when decelerating and caused less hydrocarbon emissions. Many 1970 Ford V8's, including high performance engines, used these dual diaphragm advance units.

To OP, if you are still using a Ford distributor (or rebuilt Ford) and not a high performance aftermarket unit, you can adjust the vacuum advance canister with a 1/8" Allen wrench in the vacuum port. As others have said you need to check the specs and adjust your mechanical advance and vacuum advance. Bringing them back to stock specs should get rid of the ping.

Here are the stock specs for a 1970 460 distributor (note RPM is distributor RPM, thus 1/2 engine RPM).

Mechanical Advance:

0@500 RPM
11@2575

Vacuum Advance:

0-1 @ 5 Ins HG
12 @ 25 Ins HG

Dwell Angle:
26-31

Static Timing:

6 BTDC

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#3384857 - 05/30/14 12:18 PM Re: Pinging goes away after vacuum adv disc - why? [Re: 440Magnum]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 14253
Loc: Sunny Florida
Originally Posted By: 440Magnum
Originally Posted By: SteveSRT8
Where is the distributor machine? Find a speed shop that has one and tailor the timing as you want it.

It's fully adjustable...



Find a speed shop with someone who still knows how to operate the distributor machine.

:-P


Got one right here in the backwoods of Florida! It's hardly rocket science, as Volvohead says you can also do this in the driveway with hand tools.

I always used to set my distributor vehicles by ear anyway, only use a machine on specific cam and head combos that had some specs supplied. And of course you remember my remark a LONG time ago how we called it "vacuum retard" not advance? Just depends on the setup.

Without knowing the cam specs that compression seems kind of low, but maybe we're going for regular fuel?
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#3384891 - 05/30/14 12:55 PM Re: Pinging goes away after vacuum adv disc - why? [Re: Oldswagon]
Volvohead Offline


Registered: 05/25/05
Posts: 3335
Loc: SE Pa
Originally Posted By: Oldswagon
Most Ford's reduced ignition timing at idle by way of a dual diaphragm vacuum advance unit.


NOT in 1970, NOT in a standard "cobrajet" 429/460 build on an AUTOMATIC.

At that time, this engine series was the latest "IMCO" design, didn't need air pumps, a two port diaphragm, or any other emissions control, until at least '71 (I think it was even later, but it's been a lot of years).

The dual diaphragm distributor was also typically used on manual transmission vehicles early on, and on other engine families:

http://www.428cobrajet.org/id-dist-vac-advance

Sometime after '71, Ford dropped the compression on the 460s down near 8:1. There is a huge difference between a 385 series engine from '68-'71/72 and the later ones.

By the mid '70s they were ALL loaded down with emissions junk (including dual diaphragm advance), castrated down to lower compression, and running on unleaded swill.

But the early ones (like this one) were real beasties, with compression as high as 11:1. And they all had single diaphragm advance. And with the C6, the fuel and ignition systems were very simple and dependable.

The SCJ (Super cobrajet) and Boss versions were altogether another build, with the Boss having PITA head gaskets and being completely unmanageable on the street.

This distributor fitted about 8 different engines, not just the 385 series. So you will see rebuilders fitting them with replacement distributors and advance units showing two vacuum ports. But that's WRONG, and not what the early ones came with.

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#3384892 - 05/30/14 12:57 PM Re: Pinging goes away after vacuum adv disc - why? [Re: SteveSRT8]
wag123 Offline


Registered: 06/14/11
Posts: 490
Loc: Texas
Guys, the OP obviously does not have a stock engine. The hardware, vacuum connections, and timing settings you are referring too are for a stock-from-the-factory early emissions controlled engine. All of my advice was on to how the OP could get the best street driveability and fuel mileage out of his less-than-stock setup based on my past experiences doing this sort of thing (he is already getting his full measure of WOT performance from having it dyno-tuned).
BTW, the advice I gave about timing settings assume that the distributor's centrifugal advance is working properly and it's advance curve set-up properly. The dyno tuner should have done this for him.
You don't need to take the distributor to a shop to get it setup. For as little as $50-$70 one can obtain an adjustable advance timing light, and for under $20 one can obtain a fairly accurate vacuum gauge. Using these simple tools one can see EXACTLY what is going on with this engine and make the necessary modifications/adjustments as needed, IN THE DRIVEWAY. Distributor advance springs, weights, and other parts are quite inexpensive (if needed). If the OP doesn't already have an adjustable vacuum diaphragm, these can be purchased for $30 to $50.


Edited by wag123 (05/30/14 12:59 PM)

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#3384915 - 05/30/14 01:38 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
Volvohead Offline


Registered: 05/25/05
Posts: 3335
Loc: SE Pa
Yes, it would be helpful if the OP explained exactly what he had at this point.

But unless this has been fitted with an aftermarket distributor, I think it's most likely a mechanical advance fault. The vacuum motors typically malfunction open. The only other possibility is if someone removed the vacuum calibration spring.

But until he clarifies, it is all so much speculation.

I still don't get castrating down a pre-smog engine like this. They run fine on 93 with simple steps.

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#3384930 - 05/30/14 02:02 PM Re: Pinging goes away after vacuum adv disc - why? [Re: Volvohead]
Oldswagon Offline


Registered: 01/23/03
Posts: 761
Loc: ON
Originally Posted By: Volvohead


NOT in 1970, NOT in a standard "cobrajet" 429/460 build on an AUTOMATIC.

A


Who's talking about 1970 429CJs?? And that link was for the 428 CJ engines. This is a 1970 460-4V from a Mark III, a car that ran 17 sec 1/4 mile times. That said, I pulled my 1970 Motor Trend where they test a 1970 Torino 429CJ vs a Chevelle LS6 454 and a 440 Road Runner. There is a clear under the hood shot on the Torino showing a dual diaphragm vacuum advance canister.

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#3384935 - 05/30/14 02:12 PM Re: Pinging goes away after vacuum adv disc - why? [Re: wag123]
440Magnum Offline


Registered: 02/01/09
Posts: 6099
Loc: Texas
Originally Posted By: wag123
I beg to differ 440. I have a LOT of experience in this area.
Ported verses manifold vacuum control of the vacuum distributor advance is a much discussed and widely misunderstood topic. From Lars Grimsrud... "Ported vacuum was used as an emissions control method to retard timing at idle (by eliminating vacuum advance) in order to reduce hydrocarbon emissions."
Just because the vacuum advance is plumbed to the carburetor does NOT mean that it is ported (throttle plate controlled) vacuum. In most cases, this is just a convenient place to put a DEDICATED manifold vacuum port (note in a couple of the attached articles that they tell you NOT to run a "T" in another manifold vacuum line to get your vacuum for the distributor).

To back up what I said, here are some articles...
http://www.460ford.com/forum/showthread.php?t=117504
http://w2ner.com/distributors.htm
http://www.camaros.org/pdf/timing101.pdf
http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf
http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/Vaacuum_Advance_Specs.pdf

There is a wealth of additional information on the internet about this topic.
I can attest to what they talk about in these articles from personal experience over the last 45 years. There is one thing mentioned in one of the articles that I disagree on, I have found that you should NOT have full vacuum advance at idle. This can cause problems like the OP is experiencing. Most vacuum diaphragms have enough of a response delay in them that they won't cause a idle fluctuation at small idle vacuum variations.
I can also tell everyone from personal experience that IMHO, on a carbureted street driven non-emissions-system-equipped high performance vehicle, you should ALL be using a vacuum advance distributor and you should ALL be using manifold vacuum to control it.


Don't know what to say, other than "my ~35 years of experience is in direct opposition to yours." Mopar NEVER used manifold vacuum. I have less experience with Ford, what I do have is similar. I indeed know that most carbs have a ported vacuum and a manifold vacuum fitting... but at least 80% of the stock setups I've personally dealt with used the ported vacuum nipple. I know for a fact that all the following used ported vacuum from the factory: '49 Plymouth flathead, '66 Plymouth 361, '66 Dodge 383, '65 Chrysler 300L, '69 Coronet R/T 440, '69 Ford Ranchero 302, '73 Satellite 318 (with OSAC- Orifice Spark Advance Control- added for emissions), 74 Mercury Comet 250 1V, 74 Dart 318 (with OSAC added for emissions).

OSAC was a driveability and fuel economy nightmare intended to reduce NOx. It took ported vacuum as the input, and once the engine was at operating temperature it routed the vacuum signal through a check valve with a TINY pinhole so that it took many seconds for the distributor advance chamber to pump down, but the vacuum would all be dumped very quickly when the vacuum signal went away. So a short stoplight-to-stoplight run would never let the vacuum advance engage at all. It pretty much took vacuum advance out of the picture for city driving, and you only got full advance during steady cruising on the highway. And one blip of the throttle would dump all the built-up vacuum and you started over again. Not to mention the fact that the orifice would clog easily, which just killed the vacuum advance ALL the time.

Incidentally, there's one other thing that's dead wrong in the article you quoted. It says that using ported vacuum is an emission control device used to lower hydrocarbon emission. Using ported vacuum at idle lowers NOx, and actually RAISES hydrocarbon emissions. Running a ton of advance at low RPM creates higher peak combustion temps, which directly contribute to NOx emissions. Simlarly, a later spark can result in less complete combustion, raising unburned HCs. So its really not an emissions winner either way.


Edited by 440Magnum (05/30/14 02:24 PM)
_________________________
'66 Dodge Polara & '69 Dodge Coronet R/T both 440/727
'08 Ram 1500 4.7/545RFE
'12 Challenger SRT8 392/6-speed
'99 Cherokee 4.0, '11 Grand Cherokee 3.6

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#3385012 - 05/30/14 03:55 PM Re: Pinging goes away after vacuum adv disc - why? [Re: 440Magnum]
wag123 Offline


Registered: 06/14/11
Posts: 490
Loc: Texas
Originally Posted By: 440Magnum
Incidentally, there's one other thing that's dead wrong in the article you quoted. It says that using ported vacuum is an emission control device used to lower hydrocarbon emission. Using ported vacuum at idle lowers NOx, and actually RAISES hydrocarbon emissions.

You are absolutely right! I didn't catch that one.
Now, the OP's car COULD have the centrifugal advance curve set up in such a way that it is advancing WAY too early in the RPM range (like just off of idle). Adding-in vacuum advance can push it over the top and cause the pinging. On engines that I set up for the street, I like to have the centrifugal advance start to move at 1500 to 1600 RPMs and be all-in by about 2700 to 2800 RPMs. But, with only a 8.5:1 compression ratio, he should be able to run a TON of advance and still not have it ping. Using 93 octane fuel, at that compression ratio he should be able to run as high as 52 degrees of total advance at as low as 2500 RPMs without a pinging problem. That is why I mentioned the carburetor power valve. It could be either... way too lean or not functioning at all.
All of the possibilities we are throwing out are just guesses. First off, we don't know what he is running for a cam or carburetion. And, until the OP puts a timing light and vacuum gauge on it, ALL we can do is guess about what the possible problem might be.


Edited by wag123 (05/30/14 04:05 PM)

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#3385045 - 05/30/14 04:39 PM Re: Pinging goes away after vacuum adv disc - why? [Re: wag123]
440Magnum Offline


Registered: 02/01/09
Posts: 6099
Loc: Texas
Originally Posted By: wag123
Originally Posted By: 440Magnum
Incidentally, there's one other thing that's dead wrong in the article you quoted. It says that using ported vacuum is an emission control device used to lower hydrocarbon emission. Using ported vacuum at idle lowers NOx, and actually RAISES hydrocarbon emissions.

You are absolutely right! I didn't catch that one.
Now, the OP's car COULD have the centrifugal advance curve set up in such a way that it is advancing WAY too early in the RPM range (like just off of idle). Adding-in vacuum advance can push it over the top and cause the pinging. On engines that I set up for the street, I like to have the centrifugal advance start to move at 1500 to 1600 RPMs and be all-in by about 2700 to 2800 RPMs.


I think you're right.

From what he said about the dyno shop, I really think they did a pretty good job... of setting it up to run its best WITHOUT a vacuum advance. I've seen a lot of strip cars set up that way, and you can't just hook the advance back up and go drive it on the street (usually) once that's done. Gotta set up both together if you're ever going to use vacuum. The old Mopar big-block wedge head rule-of-thumb for no vacuum advance and dragstrip use was "38 degrees total advance, ALL IN BY 1200 RPM (then adjust from there for your specific cam)." HAving all the mechanical advance in that fast just will not work with vacuum advance in the mix.

Total advance is VERY dependent on combustion chamber shape, too. The Hemis and wedge big-blocks liked different amounts of total advance, even with the same rotating assembly and similar cam profiles.
_________________________
'66 Dodge Polara & '69 Dodge Coronet R/T both 440/727
'08 Ram 1500 4.7/545RFE
'12 Challenger SRT8 392/6-speed
'99 Cherokee 4.0, '11 Grand Cherokee 3.6

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#3385054 - 05/30/14 04:49 PM Re: Pinging goes away after vacuum adv disc - why? [Re: Oldswagon]
Oldswagon Offline


Registered: 01/23/03
Posts: 761
Loc: ON
Originally Posted By: Oldswagon
Originally Posted By: Volvohead


NOT in 1970, NOT in a standard "cobrajet" 429/460 build on an AUTOMATIC.

A


Who's talking about 1970 429CJs?? And that link was for the 428 CJ engines. This is a 1970 460-4V from a Mark III, a car that ran 17 sec 1/4 mile times. That said, I pulled my 1970 Motor Trend where they test a 1970 Torino 429CJ vs a Chevelle LS6 454 and a 440 Road Runner. There is a clear under the hood shot on the Torino showing a dual diaphragm vacuum advance canister.



I forgot to mention that the 429 Torino was an automatic.

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#3385060 - 05/30/14 05:06 PM Re: Pinging goes away after vacuum adv disc - why? [Re: 440Magnum]
wag123 Offline


Registered: 06/14/11
Posts: 490
Loc: Texas
Originally Posted By: 440Magnum

The old Mopar big-block wedge head rule-of-thumb for no vacuum advance and dragstrip use was "38 degrees total advance, ALL IN BY 1200 RPM (then adjust from there for your specific cam)." HAving all the mechanical advance in that fast just will not work with vacuum advance in the mix.

Now THAT explains a LOT!!!
If this is indeed the case, the OP will need to start from scratch with his distributor setup and timing settings. The good thing is that, done right, he won't loose any of the power that the engine makes at WOT.

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#3385078 - 05/30/14 05:44 PM Re: Pinging goes away after vacuum adv disc - why? [Re: wag123]
wag123 Offline


Registered: 06/14/11
Posts: 490
Loc: Texas
Thanks for jogging my aging and increasingly feeble memory 440! I had forgotten all about that.
Back in the day (many, MANY moons ago) when I was into drag racing, that is EXACTLY how we setup the timing on our drag race engines. It is how we made the cars come out of the hole like BIG DOGS! But, this was on DEDICATED drag cars, not street cars that served as daily use transportation and occasionally drag raced on a Friday night now and then.
Putting an adjustable timing light on the car will tell the truth IMMEDIATELY!


Edited by wag123 (05/30/14 05:49 PM)

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