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Old 11-30-2021, 08:12 PM   #1
jhljr44@yahoo.com
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Default 1955 F-100 5.0L timing

What is the best method for timing my 5.0L 4v carburetor V8. Do I use the vacuum above or below the throttle plates?
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Old 11-30-2021, 08:37 PM   #2
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Default Re: 1955 F-100 5.0L timing

What year and donor vehicle is the engine from, also the make and model of the carburetor and ignition system?

Intake manifold vacuum can be used to adjust the initial timing, with the line to the vacuum canister on the distributor disconnected and plugged while setting the initial timing.
The line for the distributor vacuum canister from the carburetor is 'ported' vacuum, above the throttle plates.

.

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Old 11-30-2021, 10:07 PM   #3
Ole Don
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Default Re: 1955 F-100 5.0L timing

For timing, use manifold vacuum, under the throttle plate. Advance the timing to the maximum steady vacuum, then back off just a bit, maybe 1/2 inch of vacuum. Tighten down the dizzy and test drive it. During the test, lug the engine just a bit and listen for ping. If no ping, you are finished. If it pings, back it off just a bit more.
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Old 12-01-2021, 09:34 PM   #4
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Default Re: 1955 F-100 5.0L timing

84 FMC short block 5.0L. Edelbrock dual plane 4bbl aluminum performer intake with Edelbrock 4bbl carb. New standard ford dizzy.
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Old 12-01-2021, 11:27 PM   #5
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Default Re: 1955 F-100 5.0L timing

By trying to set the timing by vacuum, at idle, you are not compensating for the mechanical advance. Use a timing light, ideally 36 to 38 degrees total (vac & mech) advance is where you need to be. Not to be picky, but Fords work best with venturi vacuum (above the throttle plates)
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Old 12-02-2021, 09:53 AM   #6
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Cool Re: 1955 F-100 5.0L timing

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- POSSIBLE START of NEW FOOD FIGHT -

What is being discussed is BASIC INITIAL TIMING, finding optimum initial timing set through use of the manifold vacuum reading (same as carb idle/balance adjustment).

You are describing POWER TIMING in a sense. But the reference to use of ported vacuum for the vacuum advance is correct (IMO).

Of course one would verify timing with a light after using this method to insure there is not too much advance.
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Old 12-02-2021, 10:05 AM   #7
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Question Re: 1955 F-100 5.0L timing

Quote:
Originally Posted by jhljr44@yahoo.com View Post

New standard ford dizzy.
I a$$-u-me you are describing a rebuilt points style or possible DS-II OEM DIST?
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Old 12-02-2021, 10:36 AM   #8
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Default Re: 1955 F-100 5.0L timing

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Originally Posted by craig View Post
Use a timing light, ideally 36 to 38 degrees total (vac & mech) advance is where you need to be.
No, "total timing" is always determined without vacuum advance. Most OHV V8 want 34° to 36°, somewhere in there anyway. On flat ground, cruising out on the highway 50° or even more is typical.
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Old 12-02-2021, 11:18 AM   #9
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Default Re: 1955 F-100 5.0L timing

Take a look at factory specs on any Ford, GM or Mopar from the 60's. The mechanical system was good for 12-16 degrees, add that to the base timing from 2-12 degrees and you had from 14 to 28 degrees total mechanical advance. Many early vac advance cans from Ford were adjustable either with washers/spacers or an allen wrench. Ideally 38 degrees grand total will be cleaner, outperform and get better mileage than the missfire that is created with 50 degrees. Put the vehicle on a chassis dyno and watch the hydrocarbon level climb at 50 degrees
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Old 12-02-2021, 11:59 AM   #10
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Default 1955 F-100 timing

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Originally Posted by craig View Post
Take a look at factory specs on any Ford, GM or Mopar from the 60's. The mechanical system was good for 12-16 degrees, add that to the base timing from 2-12 degrees and you had from 14 to 28 degrees total mechanical advance.
The factory specs in the manuals were ordinarily listed as distributor degrees, because, the OEMs intended for the distributor to be setup on an actual distributor machine. This is the source of much of the confusion with so many people. The distributor or course turns at half speed relative to the crankshaft, therefore the actual advance degrees are double when observed with a timing light. A "10L" reluctor slot for example is 20° of advance at the crankshaft.

"Total timing" is an old drag racing term, they don't even have a vacuum advance installed on the distributor. That's kind of how the term got started most likely. And they will often lock out the distributor completely to 34° or 36°.


Quote:
Put the vehicle on a chassis dyno and watch the hydrocarbon level climb at 50 degrees
Well pollution levels are a whole 'nother subject! No argument there. NOX was °the bugaboo in the 70s, which is why they crippled everything to meet federal requirements.

The stock factory manual specs for '64 shows a "total" total of mechanical + vacuum possible advance of roughly 48° BTDC under steady cruise condition. It does require a sharp tune with a good hot ignition spark to reliably ignite lean fuel mixtures.

But that's the story why so much ignition advance is necessary under those conditions (that's why vacuum advance was invented in the first place) there was simply no way to achieve the necessary ignition advance curve using centrifugal weights and springs alone.
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Old 12-02-2021, 12:00 PM   #11
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Cool Re: 1955 F-100 5.0L timing

... can I start shiat or what ...

INITIAL ADVANCE and MECHANICAL ADVANCE are the only factors in TOTAL TIMING ADVANCE. The manifold vacuum signal is not constant and drops out of the equation at higher RPM's.

VACUUM ADVANCE is for drive-ability on a street engine, not meant for a race engine (either using a mechanical distributor).
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Old 12-02-2021, 12:03 PM   #12
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Question Re: 1955 F-100 5.0L timing

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...why so much ignition advance is necessary under those conditions (that's why vacuum advance was invented in the first place) there was simply no way to achieve the necessary ignition advance curve using centrifugal weights and springs alone.
You've never seem a 3000 RPM LAUNCH on the street?
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Old 12-02-2021, 12:15 PM   #13
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Default Re: 1955 F-100 5.0L timing

I'd be wondering the same as KULTULZ on the distributor. Standard for 1984 electronic distributor or standard Ford small block distributor for 1964 thru? If it is for a 55 F-100 then it's likely not long on electronic accessories. A distributor can be set up by trial and error with a timing light that has degree adjustments or it can be set up on a distributor machine. The other thing we would have to assume is if it has a 1405 or a 1406 Edelbrock 600 CFM copy of the Carter AFB.

I'm not sure how a 1984 5.0 compares to a 1969 302 either as far as combustion chamber size and compression ratio.
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Old 12-02-2021, 12:24 PM   #14
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Exclamation Re: 1955 F-100 5.0L timing

Quote:
I'd be wondering the same as KULTULZ...

You are getting brave making a statement like that.

As most know, KULTULZ wonders about a host of things, one being which time warp he is located in ...
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Old 12-02-2021, 06:03 PM   #15
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Default Re: 1955 F-100 5.0L timing

I've had trouble in the past with some cars using manifold vacuum. Get everything set at idle and then you put in drive, rpm drops and then vacuum drops that pulls the advance down and that drops rpm further. I just seem to have better luck using the ported vacuum. All my carbed Fords came that way from the 60's to the 80's. Just my experience. Try it both ways and see which suits your engine better.
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Old 12-02-2021, 06:23 PM   #16
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Default Re: 1955 F-100 5.0L timing

It depends on the system but anything can be made to work in some way that would likely be acceptable. The old Load-O-Matics had venturi vacuum but there was no mechanical advance at all. I've seen where folks use a modified Chevy distributor with an adjustable port in the vacuum can and they set it up to use manifold pressure to operate a load control mated with the existing mechanical advance and they work pretty well. Flatheads don't need much advance. The small block Ford will likely need at least what it was set up for in 1984. If heads and cam are changed then all that may require further changes but it likely wouldn't be all that much change. On a different carb a person needs to check and see what pressure the port is supposed to give and compare that to a stock type Ford carb to see if it's compatible. They have several ports on the Edelbrock AFB carbs. A person can use them or plug them but there should be information about that in the carburetor specification sheet.

Last edited by rotorwrench; 12-05-2021 at 10:08 AM.
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Old 12-05-2021, 12:18 AM   #17
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Default Re: 1955 F-100 5.0L timing

Quote:
Originally Posted by KULTULZ View Post
You've never seem a 3000 RPM LAUNCH on the street?
I suppose, if people only drove at wide open full throttle you might have a point!

But again, there is no point to vacuum advance in drag racing in the first place, because there is basically only one engine operating condition and that's flat out wide open throttle. But we're not talking about that type of operation in ordinary passenger or street driven cars.

An engine designed to be driven on the street, puttering around town at part load throttle and varying speeds, RPM and steady cruise at highway speeds etc., requires an ignition distributor capable of controlling the ignition to meet very diverse operating conditions.

A simple centrifugal weight & spring mechanism alone could not achieve those requirements because the necessary timing advance "spread" or range for optimum fuel combustion characteristics was way too wide.

A typical OHV V8 from an engineering standpoint needs about 50° BTDC advance or more when cruising down the highway on flat ground in high gear. Drag racing engines simply don't "do" part throttle cruising, so it's irrelevant. If the distributor springs were light or flexible enough in a passenger car to allow for that much ignition advance at highway cruise, if the reluctor slots were long enough for that, then the engines would have been grenading left and right simply by driving normally around town. To get around this problem they ingeniously utilized engine manifold vacuum as an engine load-based signal to supplement centrifugal advance and met ignition advance requirements that way.

It is possible to use the engine itself as a kind of "distributor machine" for tuning purposes, but the only point I was making earlier was that the specification listed in the shop manual, the nominal numbers themselves listed, are exactly half of what actually appear at the crankshaft. This was because of the assumption by Ford that a distributor was being set up and tested on a distributor machine, not by Joe in his garage with a timing light.
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Old 12-05-2021, 02:32 AM   #18
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Question Re: 1955 F-100 5.0L timing


How in the world did a very simple question (arriving at peak timing using manifold vacuum) turn into a total ignition theory discussion?

You can operate a fully mechanical distributor on the street. FORD offered it for years. The only true benefit of vacuum advance is fuel economy, street-ability and emission requirements.

How the advance curve is set up is how street-able the car will be. A SATURDAY NIGHT SPECIAL, not that big of a deal.

Here is the correct answer to the OP's question -

Quote:
Originally Posted by Ole Don View Post

For timing, use manifold vacuum, under the throttle plate. Advance the timing to the maximum steady vacuum, then back off just a bit, maybe 1/2 inch of vacuum. Tighten down the dizzy and test drive it. During the test, lug the engine just a bit and listen for ping. If no ping, you are finished. If it pings, back it off just a bit more.
Add no run-off after engine shut-down and you have it.

... sheesh ...
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Old 12-06-2021, 10:12 AM   #19
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Default 5.0L timing

Quote:
Originally Posted by KULTULZ View Post

How in the world did a very simple question (arriving at peak timing using manifold vacuum) turn into a total ignition theory discussion?
Well no, actually he asked how to "best" set the base ignition timing. I suggest using a timing light.

Quote:
You can operate a fully mechanical distributor on the street.
Yes, we all know this. Nobody said otherwise. I don't get it, generally you always seem to want to argue against points nobody has made, generally crapping on threads, and stinkin' up the forums that way.
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Old 01-15-2022, 09:55 PM   #20
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Default Re: 1955 F-100 5.0L timing

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