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School me.

I understand that there is initial advance adjusted with timing, mechanical advance adjusted with weights and springs in the distributor and vacuum advance, IDK how vacuum advance is adjusted or if it is possible.

My car is 55 years old. How do I know if I have the correct weights and springs and correct vacuum advance unit?

Are all 289-302 distributors the same or close to the same? It seems higher hp engines would have a different requirement and a different requirement to meet whatever smog regulations were in effect when the car was produced.

finally, Im guessing parts store distributors are a one size fits all part. Does that matter?
 

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The best way to know?....ship to Dan Nolan at the Mustang Barn in Harleysville Pa. Based on the results of a few questions, he'll check your distributor out, make recommendations as to what needs attention and pre-set your mechanical, vacuum canister and recommend an initial advance. Also, recurve it for best performance. Mine was mechanically sound, just needed a recurve and changes to my current initial and vac advance. Then you'll know for sure.
 

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If you are questioning if the vacuum advance works. You can test it with a mity-vac. This will also let you know how much vacuum it takes to get it movin. If you know your vacuum at an idle then you can determine if you have the appropriate vacuum advance unit. (at least as far as getting it to advance, the amount it should advance you'll need to look up). If you have a dial back timing light you can back into the mechanical advance. When it starts to come in and the total mechanical advance.

I'm short on details here. Just saying it can be done. I'm sure there are articles out there on the interweb. If I wasn't supposed to be working I'd find one for you.

(edit)
Found an article. They're talking about a chevy motor but they are all suck, squeze, bang, blow. Concepts are the same. https://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/
 

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The shop manual give you the specification for Initial, centrifugal and vacuum advance. This was stuff me and my friends were doing when we were 16. None of us would have ever though about paying somebody to set timing. So there is no reason you cannot do this yourself unless you think a 16 year-old is smarter than you which having once been one myself I can guarantee they are not. They do have more ambition than smarts where I have the knowledge and no longer any ambition. IIt seems like your not allowed to have both. This is the most basic car you can work on. You need a adjustable timing light. It must be "adjustable" Do not buy a timing light unless it is what? ADJUSTABLE! Then you need a handheld vac cum pump. You can buy the tools, do it yourself and then always have the tools for what it would cost to pay somebody. I bought a great adjustable timing light recently at an estate sale. New in the box for $20.00 and it wasn't a junk one. It had belonged to a brain surgeon that got brain cancer. That just doesn't seem right that he was sacrificed so I could get a timing light cheap.
 

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If your distributor hasn't been modified, it's a pretty good guess it still has the stock advance weights & springs. If that's what you're looking for, just buy a reman and you're home free.
 

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I forgot to answer one of your questions. Some vacuum advances are adjustable and some are not. The adjustable ones I have worked on you unplugged the vacuum hose and stuck an Allen wrench inside the hole. Then you could adjust the stop for that the diaphragm hits.

With an adjustable timing light you set the adjustment to zero and read your initial timing with the light just like you would with any old timing light. With the hose unplugged from the advance unit you raise the rpm watching the timing mark advance. When it does not advance anymore and keeping the same rpm you rotate the adjustment wheel on the timing light until it moves the timing mark back to where you started. Then you look at the timing light adjuster and it will show you how many degrees you had to rotate the adjuster to reach your starting point. That number of degrees is your total centrifugal advance. Remember you had the vacuum advance disconnected so it was turned off. You have not touched the timing, nothing with the actual timing has bee changes. The adjuster on the timing light is altering when the light flashes allowing you to see how many degrees the timing has changed from the starting point. A must have tool.

For the next test you do not need to raise the rpms. Reset your timing light back to zero. Stick a handheld vacuum pump (another must have tool) on the vacuum advance and pump up the vacuum and you will see timing mark start to rotate until it stops. Same thing, look at how many degrees you need to adjust the timing light to bring the mark back to your starting point.

Add the three up, your initial timing, centrifugal advance and vacuum advance, That is you total timing advance. That is very important for maximum power and fuel economy. Too much total advance and the engine can be damaged because of detonation.

Hook the hose back on the advance. Set the timing light back to zero and open the throttle to verify your total advance. This lets you know that the vacuum advance is getting venturi vacuum.

Always adjust point gap first because changing the point gap effects dwell, the amount of time the coil is building up voltage but it also changes the timing. Change the point gap and you have changed the timing.

Then adjust the timing, V=because adjusting the timing has no effect of the point gap and dwell.

Last, adjust the idle air fuel mixture and idle speed screw because everything you change has an effect on the air fuel mixture.
 

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If your distributor hasn't been modified, it's a pretty good guess it still has the stock advance weights & springs. If that's what you're looking for, just buy a reman and you're home free.
Well, I suspect the OP's car runs with his existing distributor. I suspect it would run with a stock or remanufactured distributor, but that does not mean that it will run optimally. Reman distubutors are slapped together and NOT tested for curve. What may work "okay" for a stock engine may leave a lot on the table for a modified engine. A camshaft can significantly change the vacuum signal and the advance curve should adjust for that. A skilled tuner with a Sun testing machine can dial in what is best for a particular car's setup and intended driving style. Anyone that wants to make sure their distributor is tuned as well as it can be for their car should consider shipping it off to Dan at the Mustang Barn. $85+ shipping is worth it.
 

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If your distributor hasn't been modified, it's a pretty good guess it still has the stock advance weights & springs. If that's what you're looking for, just buy a reman and you're home free.
Most re-man distributors come out of the box with poor quality control and need to be re-curved worse than a worn stock one. They are clean and have new bearings, and a generic spring and weight setup to fit a broad number of applications.
 

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What would a stockish setup for advance look like?
12 INITIAL, 20 MECH, 6 VAC?

In particular, what is most common figure for Vac Advance you all use/see?

Sent from my SM-G950F using Tapatalk
 

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Playing with advance is tricky - not rocket science but tricky. The HR article mentioned is a very good read, one thing I did not know is that a Hex on the Vacuum adv usually means its adjustable. All the Vacuum advances I have had in my junk box dizzys turned out to be adjustable. I thought one wasn't but it turned out when I reamed the hole a little and put the next size allen in it, it was adjustable. I even took one apart to see how they work - unscrewing the allen wrench limits the VA. At one point I had to dial back my VA because it stalled my motor at idle and made it pop in the exhaust. I kept an allen wrench in the ash tray and every time it popped, I backed it out one flat. I bought a new one and for some reason I could run it unaltered, perhaps the old spring was rusted through. The old VA went from 12-15mpg when I finally smartened up and hooked up the VA, and the new VA added 2 more mpg getting me to a little more than 17 mpg.

A skilled distributor guy will take knowledge of your cam profile and engine build and dial in a distributor. For all the years I have been on this site, people overwhelmingly report back big smiles when they spend $100 and send their dizzys to Dan Nolan. Mine was "swung" just before I bought my motor, otherwise I would do so. Might be worth sending it out once and being done with worrying about this variable.
 

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What would a stockish setup for advance look like?
12 INITIAL, 20 MECH, 6 VAC?

In particular, what is most common figure for Vac Advance you all use/see?

Sent from my SM-G950F using Tapatalk
For a stock 1968 J-Code 302 engine with a T5 transmission, my setup is as follows:
Initial: 12*
Mechanical max: 26* (-> "all in" advance = initial + mech = 38*)
Vac advance: 15*
Hooked vac advance to manifold vacuum

Some good references...


 

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For a stock 1968 J-Code 302 engine with a T5 transmission, my setup is as follows:
Initial: 12*
Mechanical max: 26* (-> "all in" advance = initial + mech = 38*)
Vac advance: 15*
Hooked vac advance to manifold vacuum

Some good references...


Good info, thanks..15° is about 8° more than I'm running..I'll experiment with some more vac advance.
Vac Advance is a dark science, and very few articles offer up any ballpark figures (that I have found)

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Good info, thanks..15° is about 8° more than I'm running..I'll experiment with some more vac advance.
Vac Advance is a dark science, and very few articles offer up any ballpark figures (that I have found)

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Not quite a dark science...just one that some find hard to understand (like electricity)...

To put things simply, the fuel/air mixture in your engine takes a specific time to burn completely. If engines ran at a constant rpm, like a lawnmower, one set timing specification would work fine. Since the operating range varies over (typically) 4 - 5,000 rpm the point at which the spark ignites the mixture has to vary.

The factors that affect just WHEN that spark needs to occur include engine rpm, of course, fuel/air mixture ratio, engine load, cylinder temperature and some others. Modern computer-controlled ignitions can plot this down to a split second due to the sensors and computing power built into the processor controlling ignition. Older "analog" cars can't do this so precisely. It looks like you understand MECHANICAL or "centrifugal" advance so let's discuss vacuum advance.

Vacuum spark advance was developed as an option for older vehicles to improve fuel mileage. Early versions were marked as "Economizers". The "dark science" is that when the engine is not under load (closed throttle) a greater amount of spark advance can be employed which will more completely burn the fuel mixture, adding to combustion efficiency. More heat from the fuel... more energy to the piston....more power and.... mileage. Since the engine isn't under any kind of load, cylinder pressures are low and there is little chance of "pre-ignition" due to heat and pressure in the cylinder or detonation due to multiple flame fronts caused by lighting off the mixture too early (plus trying to shove the piston backward during the compression stroke). Utilizing VACUUM to control this extra advance made perfect sense as the vacuum signal decreases as velocity through the carburetor increases.... the more you put your foot into it, the lower the vacuum signal, so as the engine LOAD increases the vacuum SIGNAL decreases and the amount of spark advance DECREASES to keep the engine from "pinging". At the same time, MECHANICAL advance is increasing as engine rpm increases so less ADDITIONAL spark advance is needed.

The "voodoo" involved is being able to calibrate BOTH systems, mechanical AND vacuum, to get the point of ignition right where the engine LIKES it. While it can be done on a "general" basis we have to remember that every BUILD is a departure from the norm and may require some "tweaks" to get perfect. In that way, an engine or chassis dyno is really the only sure way of determining the best advance CURVES (a graphical representation of the optimal spark advance settings over an rpm and/or vacuum range) although you can get close by charting the timing settings over repeated times runs over distance, such as 60 or 100 foot dragstrip times or even 0-60 acceleration.

Hope this helps explain some of that "dark magic". LOL.

Also, FWIW, the more spark advance an engine can tolerate well, the more heat from combustion is transferred into linear motion and the less WASTE HEAT is passed into the exhaust and cooling systems, meaning an engine that runs better and cooler.
 

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Thanks Bart, I guess that is where I have trouble, without a chassis dyno, it's tricky to know whether ones adjustments/settings are perfect.. Might need to book some dyno time..

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Add the three up, your initial timing, centrifugal advance and vacuum advance, That is you total timing advance. That is very important for maximum power and fuel economy. Too much total advance and the engine can be damaged because of detonation.
While I agree with most of what you wrote I am pretty sure that vacuum advance is not part of the total advance. It only comes in to play at idle(if you run full vacuum) initial acceleration before mechanical advance takes over, and part throttle cruising where vacuum is high and the the engine benefits from higher advance.

Also to the OP you can look in your stock Ford distributor and see that inside there is a double sided arm with numbers stamped on either end. This is called the reluctor. It will be stamped with two different numbers maybe 10L, 13L, 15L etc. One will always be lower than the other. Depending on which side the arm the distributor is set to will determine your total centrifugal advance. The number x 2 will give the degrees. So if you see 10L you will get 20 degrees mechanical advance. 15L will give you 30 degrees. So if you know you initial timing you will have an idea of your total advance. Of course this is verifiable using an adjustable timing light. It's possible to pull the distributor apart and switch sides on the reluctor to change total advance. You can also place a small piece of rubber tubbing or heat shrink tubing on the stop for the reluctor to limit advance as well.

Changing or adjusting tension on the springs inside the distributor will adjust the rate at which the mechanical advance arrives at full advance. Ideally you want full advance by 3000 rpms. A good shop with a sun machine can do this easily but those of us without a sun machine have do this with the engine in the car with a timing light and tachometer. It takes a little trial and error and lots of pulling the top of the distributor apart but you can achieve good results.
 

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While I agree with most of what you wrote I am pretty sure that vacuum advance is not part of the total advance. It only comes in to play at idle(if you run full vacuum) initial acceleration before mechanical advance takes over, and part throttle cruising where vacuum is high and the the engine benefits from higher advance.

Also to the OP you can look in your stock Ford distributor and see that inside there is a double sided arm with numbers stamped on either end. This is called the reluctor. It will be stamped with two different numbers maybe 10L, 13L, 15L etc. One will always be lower than the other. Depending on which side the arm the distributor is set to will determine your total centrifugal advance. The number x 2 will give the degrees. So if you see 10L you will get 20 degrees mechanical advance. 15L will give you 30 degrees. So if you know you initial timing you will have an idea of your total advance. Of course this is verifiable using an adjustable timing light. It's possible to pull the distributor apart and switch sides on the reluctor to change total advance. You can also place a small piece of rubber tubbing or heat shrink tubing on the stop for the reluctor to limit advance as well.

Changing or adjusting tension on the springs inside the distributor will adjust the rate at which the mechanical advance arrives at full advance. Ideally you want full advance by 3000 rpms. A good shop with a sun machine can do this easily but those of us without a sun machine have do this with the engine in the car with a timing light and tachometer. It takes a little trial and error and lots of pulling the top of the distributor apart but you can achieve good results.
Suppose you’re cruising at 3,000 rpm (and thus have maximum mechanical advance) and you let off the gas (going downhill, slowing, etc.) resulting in engine vacuum, won’t this create vacuum advance on top of the total mechanical advance? Or so it seems to me. Am I missing something here?
 

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Suppose you’re cruising at 3,000 rpm (and thus have maximum mechanical advance) and you let off the gas (going downhill, slowing, etc.) resulting in engine vacuum, won’t this create vacuum advance on top of the total mechanical advance? Or so it seems to me. Am I missing something here?
Yes maybe, but why are you that concerned with advance while coasting?
 

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Here's a excerpt from Crane Cams on adjusting vacuum advance-
With the vacuum hose disconnected and plugged, set the initial timing at 2° advance from factory specifications and make full throttle acceleration runs, listening for audible spark knock. If spark knock occurs, then retard the initial timing 2° and check for spark knock by making another full throttle acceleration run. If spark knock stops, you have the ideal centrifugal advance curve. If spark knock continues, then select the next heavier spring combination and repeat the test procedure. If no spark knock occurs on the first test, select the next lightest combination and repeat the test
Due to the ever lowering octane rating of gasoline in the US, we recommend you choose a centrifugal spring on the heavy side rather than light.
Test-drive the vehicle in the city and on the highway while listening for audible spark knock under heavy load and part throttle. If spark knock occurs under part throttle conditions, a change in the vacuum advance curve is needed. This adjustment is made by inserting the 3/32" allen wrench into the vacuum advance unit and turning the adjuster counterclockwise two turns at a time, testing the vehicle after each change, until part throttle spark knock is eliminated.
 
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