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Old 01-22-2018, 12:10 PM   #1
37fatfender
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Default Total Timing How do you measure it?

I am confused as what constitutes total timing. I have read places that all that counts is the initial and mechanical added together equals "Total Advance". That the vacuum advance is not figured into the equation.
I run a modified 8ba with pretty high compression, I have a MSD ready to run dizzy. Its all in at about 2600 rpm. I set my initial and with a digital timing light dial in 26 degree rev the engine adjust the dizzy to line up the marks and lock it down. I then reconnect the vacuum and then my timing is way over 26 degrees.
Am I doing things right?
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Old 01-22-2018, 12:36 PM   #2
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Default Re: Total Timing How do you measure it?

Sounds good to me
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Old 01-22-2018, 01:15 PM   #3
51 MERC-CT
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Default Re: Total Timing How do you measure it?

Seem to recall, Mech., 20° all in at 2000 rpm with vac somewhere around 2800 rpm
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Old 01-22-2018, 01:36 PM   #4
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Default Re: Total Timing How do you measure it?

Shouldn't you be setting it with the vacuum advance hooked up? If you're looking for 26 degrees total advance, it should include the part provided by the vacuum.
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Old 01-22-2018, 02:55 PM   #5
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Default Re: Total Timing How do you measure it?

No, you set the total with the vacuum disconnected. The vacuum only advances at part throttle.
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Old 01-22-2018, 02:56 PM   #6
Ol' Ron
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Default Re: Total Timing How do you measure it?

Initial timing is not very important, The only thing it does is start the engine. Once the engine starts, it's just added to the rest of the timing curves and can be used to add or subtract from them for better power or economy. Mechanical advance set at 20@200, does not make max power. It just that it provides better acceleration, from a low RPM for street use. That's why I use 8 degrees vacuum for economy. This is where putzing comes in, all engines and drivers are different, so you add or subtract to give you the best drive ability. Tuning for power in a street engine is a waste of time and can cause an over rich condition in cruise which can wash oil from the cylinder walls causing undue wear, and it doesn't help the bearings either. Always tune for cruise, where it easier to get power through the PV and vacuum advance. Probably why they invented the double pumper. considering all the money you spent on building your engine, a good tune is cost effective.
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Old 01-22-2018, 03:19 PM   #7
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Default Re: Total Timing How do you measure it?

Were are getting confused here and we dont have all the info we need .
Ron is correct all intial timing does is help start the engine and the flathead is king here at 2-4 degrees.

Then comes mechanical advance ( controlled by engine rpm) 18-24 works good here depending on the engine ( early engine had 18 ) a later engine with cam would use 24 at 2500 rpm.

Now we add vacuum ( very hard to tune on a flathead) vacuum advance should overlap mechanical advance, manifold vac would drop under load , rpm would advance mechanical . Kinda a teeter totter effect , when ones high the other should be low. Ex: You wouldnt have high vac when reved up, and you wouldnt have rpm on decel.
A perfect world would have a steady number of advance at all times when running.
Then theres the discussion of where the vac is hooked up ported or direct???. Both have been used over the years.

My suggestion would be use mechanical on a flathead with a proper advance curve ...

A stock chev has 12 degrees mechanical (24 engine) and 7 degrees vac advance (14engine ) overlapped as you would never have high vac and high rpm at the same time.
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Old 01-22-2018, 06:17 PM   #8
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Default Re: Total Timing How do you measure it?

There sure are a lot of misconceptions about vacuum advance especially, how it works, and where to connect it, but ignition timing in general.

If you understand it you can experiment with different approaches. Each engine is a little different on what it likes, and factory curves in general were very conservative. It is true that "total" timing does not count vacuum advance. This is a source of confusion, even sometimes with people who should probably know better.

The key is to realize that vacuum advance and mechanical (centrifugal) advance are completely independent of each other. Vacuum advance is load dependent, mechanical advance is RPM dependent. On level highway at steady (part throttle) cruise speeds the engine load is low and in high gear, so is RPM. This is where vacuum advance will pull in the most advance. Maybe not a Flathead but most OHV V8 run around 50° BTDC timing under these conditions. Engine load is real low, maybe 50 hp to tool down the highway consequently mixture is lean, needing lots of lead timing to get the fire started, but the RPM isn't high enough to pull in adequate advance. Keep in mind that this 50° is only on level ground, at steady speed cruise, the slightest grade or push of the pedal/throttle and that extra advance goes away in an instant, back down to the mechanical limits of the distributor itself. It really is an ingenious system, developed before the advent of continuous sensors and computer controls.

Drag race and performance engines don't even have a vacuum advance installed because they don't ever operate under part throttle conditions. It's usually a mistake to copy racing techniques in a street driven engine. Flatheads won't tolerate near the ignition advance that more modern engines will. Why that is I don't know?

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Old 01-22-2018, 08:41 PM   #9
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Default Re: Total Timing How do you measure it?

The question was how do you measure ' total timing'. The answer would be to put the distributor on a Distributor machine which would measure the number of degrees in the dizzy. What ever you set your initial timing at, you would add to what was found in the distributor and add the two for the Total. Racers use a balancer that has been 'degreed' or a ' degree tape' has been added and raise the R.P.M. and with a timing light measure the reading when the timing mark doesn't advance any more. Hope my attempt to explain your initial question doesn't confuse the issue further.
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Old 01-23-2018, 10:37 AM   #10
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Default Re: Total Timing How do you measure it?

MEASURING TIMING??

Reading the posts on how to do this?? Once upon a time when shops actually performed "tune ups" and gasoline was 24 cents a gallon. The well equiped "service station" would have sun testers etc and when the car rolled in he would pull out the spec card for the vehicle. ( never seen any of these for a flathead and i have hundreds) but you can get the point.
This card would supply the spec for all underhood service.Including total timing , intial, mechanical and vacuum.
Thought you guys would get a kick out of this .

I guess i need to make one of these for a flathead 40s Ford car......Use this card for a template and fill in all the numbers for a six volt positive ground .???
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Old 01-23-2018, 12:50 PM   #11
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Default Re: Total Timing How do you measure it?

Yes , those spec cards are really nice to have , I acquired a few years back while attending a swap meet, the vendor was giving them away ,one to a customer, I managed to pay him a little money for the ones he had left, I see where checker and Studebaker used the chev. engines and Kaiser used the continental engines, amazing all the mixtures of parts manufactures used to keep costs under control as well as quality up. I would like to know what all I am missing out of the files I have, if for no other reason just to have a complete set, thanks for sharing.
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Old 01-23-2018, 12:55 PM   #12
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Default Re: Total Timing How do you measure it?

Making a flathead chart would be awesome , I have to ask, guess or dig into the old motors manual, and some of that info is most likely been superseded with the changes in out fuel and oils of today.
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Old 01-23-2018, 01:41 PM   #13
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Default Re: Total Timing How do you measure it?

Bubba, notice in one card it sez "Ignition Current" - "Coil to ground resistance .25 volts max"

Is that a typo, or as I suspect a voltage drop test to determine excess resistance?
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Old 01-23-2018, 01:44 PM   #14
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Default Re: Total Timing How do you measure it?

My big question to the original post is where is the vacuum source? it it from manifold or a carburetor. 8BAs were all vacuum Load-O-Matic so the 8BA type carb connect won't work with a centrifugal/vacuum type distributor. If it is from the manifold then the vacuum can needs to be adjustable to the engine's needs.

The term vacuum advance is kind of a misnomer on most ignition systems since it controls for retard under load and for starting more than it does for advance. The exception to that is the 8BA Load-O Matic which is both vacuum advance and retard since its only control is vacuum but it's a special venturi ported vacuum source.
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Old 01-23-2018, 03:32 PM   #15
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Default Re: Total Timing How do you measure it?

You mentioned that your Engine was high compression but you didn’t mention what cam was in it.
If it’s a aftermarket cam with 260-270 duration you can throw the factory specs in the garbage.
And if you have a cam that big you can forget the vacuum advance . Big cams like timing and depending how you degreed the cam in you may need to advance or retard it.
But definitely will need more initial timing than stock or your Engine will seem rich because there is not enough burn time. I like timing all in at 2000 rpm.
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Old 01-23-2018, 04:38 PM   #16
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Default Re: Total Timing How do you measure it?

Quote:
Originally Posted by Crankster View Post
Bubba, notice in one card it sez "Ignition Current" - "Coil to ground resistance .25 volts max"

Is that a typo, or as I suspect a voltage drop test to determine excess resistance?
Yep thats voltage drop on that circuit.
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Old 01-23-2018, 04:42 PM   #17
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Default Re: Total Timing How do you measure it?

Quote:
Originally Posted by Fordestes View Post
Yes , those spec cards are really nice to have , I acquired a few years back while attending a swap meet, the vendor was giving them away ,one to a customer, I managed to pay him a little money for the ones he had left, I see where checker and Studebaker used the chev. engines and Kaiser used the continental engines, amazing all the mixtures of parts manufactures used to keep costs under control as well as quality up. I would like to know what all I am missing out of the files I have, if for no other reason just to have a complete set, thanks for sharing.
Fordestes
Sun Testers sold a subscription for each year . I dont know when that started but i have a set of 1960 cards. I just moved my boxes out of storage and will check when that started and ended. Good tech for sure........
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Old 01-23-2018, 04:54 PM   #18
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Default Re: Total Timing How do you measure it?

I dont have any of those cards,But have the graphs of all the distibutors on my old cars.
I use my home made dist machine to graph out the advance curves,
I test all my distributors on it, I set them up first static on the Jig, then run them up on the machine.check the curve with both hi and low vacume.
Mate Keiths 33 had a flat spot on acceleration that was hard to find.
this is the graph of his distributor advance,you can see the bottom curve with the flat spot in.
the top one is after fitting a good replacement 11a advance unit.
that fixed it.
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Old 02-08-2018, 02:32 PM   #19
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Default Re: Total Timing How do you measure it?

Thanks for the insights
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Old 02-08-2018, 05:06 PM   #20
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Default Re: Total Timing How do you measure it?

After going through all these threads, I find some confusion in the term Nax advance. The method I use gives aprox, 28 degrees of advance in cruise. Plus or minus a few degrees. I like the mechanical advance all in at 2000 rpm. set at 16 degrees and the initial at 2/4 degrees this will give a total mech adv of 18/20 degrees at 2000 Rpm. Now the vacuum advance set at 8 degrees gives a total of around 26.28 degs total advance. At least it's just another way of saying the same thing. Confusing.
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