One more question on timing

spstan

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Not to beat a subject to death but I had one more question on total timing. As I posted earlier I had a new MSD distributor installed and my mechanic disabled the vacuum advance. He claimed the total timing (advance) was set at 34-36 degree and if he hooked up the vacuum advance there would be too much total timing and I would experience detonation. BUT I was watching a video on You Tube and the fellow (Tall John) was setting the timing on a 1970 440 engine. He set the total timing at 49 degrees at 2290 rpm and claimed this was ideal (smooth running engine and no pinging). He claimed he had seen total timing as high as 58 degrees.

Now , who to believe? I was wondering what the members of this board who have 440 engines have their total timing set. Help me understand what is the ideal total timing. Paul
 
Baack in the middle 1970s, I discovered that the Exxon service station I was patronizing, owned by the father of a high school classmate AND whom I'd become friends with, talking cars a lot (as he was a Ford guy), had a few copies of tune-up manuals/guides which he got from Exxon, during when he was doing training and afterward. Naturally, as I'd never seen those or suspected they ever existed, I asked if I could look at one.

It was geared to the service station trade at the time, which included light repairs plus oil changes. There was one section on tune-ups, including specs. In addition to the normal factory timing specs, was ALSO a column on "Advance at 2500rpm", which had numbers in the 50-55 degree BTDC range. I knew about base timing and full mechanical advance, BUT THEIR FIGURES AT 2500RPM WERE FOR MECHANICAL, BASE, AND VACUUM ADVANCE ALL TOGETHER. At first, seeing those very high advance numbers looked out of whack. THEN I started to dissect them and it all made sense, in the service station world, where once the tune-up had been done, with the base timing set and the carb adjusted, to take the rpms up to about 2500rpm for a check of total distributor operation, which would include both the vac and mechanical advance AT THE SAME TIME. Of course, at WOT, vac advance would go away as manifold vac did, leaving pure mechanical + initial timing. So, it made sense when I thought about it and figured things out.

Go into the FSM and look at distributor advance specs. You'll find three different mechanical advance numbers for three different rpm levels. Take the middle one. Then add the full vac advance numbers to that, which will be what's in the distributor. Then add the base initial timing to that. See if it does not get close to his desired amount of advance.

We are used to seeing only initial timing settings and how that might relate to 34-38 degrees BTDC total advance. We NEVER consider vac advance amounts, other than if the vac advance is leaking or whatever, as vac advance in zilch at WOT or close to it.

For what I was doing, I still used the FSM specs, fwiw.

Just some realizations I had ages ago,
CBODY67
 
Baack in the middle 1970s, I discovered that the Exxon service station I was patronizing, owned by the father of a high school classmate AND whom I'd become friends with, talking cars a lot (as he was a Ford guy), had a few copies of tune-up manuals/guides which he got from Exxon, during when he was doing training and afterward. Naturally, as I'd never seen those or suspected they ever existed, I asked if I could look at one.

It was geared to the service station trade at the time, which included light repairs plus oil changes. There was one section on tune-ups, including specs. In addition to the normal factory timing specs, was ALSO a column on "Advance at 2500rpm", which had numbers in the 50-55 degree BTDC range. I knew about base timing and full mechanical advance, BUT THEIR FIGURES AT 2500RPM WERE FOR MECHANICAL, BASE, AND VACUUM ADVANCE ALL TOGETHER. At first, seeing those very high advance numbers looked out of whack. THEN I started to dissect them and it all made sense, in the service station world, where once the tune-up had been done, with the base timing set and the carb adjusted, to take the rpms up to about 2500rpm for a check of total distributor operation, which would include both the vac and mechanical advance AT THE SAME TIME. Of course, at WOT, vac advance would go away as manifold vac did, leaving pure mechanical + initial timing. So, it made sense when I thought about it and figured things out.

Go into the FSM and look at distributor advance specs. You'll find three different mechanical advance numbers for three different rpm levels. Take the middle one. Then add the full vac advance numbers to that, which will be what's in the distributor. Then add the base initial timing to that. See if it does not get close to his desired amount of advance.

We are used to seeing only initial timing settings and how that might relate to 34-38 degrees BTDC total advance. We NEVER consider vac advance amounts, other than if the vac advance is leaking or whatever, as vac advance in zilch at WOT or close to it.

For what I was doing, I still used the FSM specs, fwiw.

Just some realizations I had ages ago,
CBODY67
So cB what is your total timing? Paul
 
Looking in the '70 FSM, first, the 383 2bbl (it seems that the distributors on these engines, all 383 2bbls, regardless of model year) usually have a pretty decent advance curve in them, usually ending up with about 34-36 degrees BTDC total at 4500rpm. Using the specs for 1700 rpm, mech +vac is right at 43 degrees BTDC. With the spec 2.5 degrees BTDC initial, that gets to about 46 degrees BTDC at 1700rpm. Going to a 440/375, that total drops to closer to 40 degrees BTDC. Raising the engine speed to 2500rpm would be more, no doubt. Going back to a '65 383 2bbl, total of 43 degrees at 1400rpm, so it could well be 49 degrees BTDC at 2500rpm or so. The '66 383 2bbl has a similar advance set-up, but with initial being 12.5 degrees BTDC. Total mechanical + initial on the '66 383-2 is 37.5, which ran well for us using premium fuel on the 9.2 rated CR. It also did 15 degrees BTDC with no problem, too, for a total of 40 degrees BTDC total. Of most of the 383 2bbls I looked at in the FSMs, most were at 43 degrees BTDC at right at 1400 rpm, fwiw.

As to the YouTube video, we do NOT know at what altitude the shop was at, do we? As that can affect how much advance the engine will tolerate, just as fuel octane will, also. The OTHER thing is that what one engine might like, another one dislikes, as to ignition advance. Key things are that it starts easy and quickly when hot or cold, NO clattering/detonation on WOT acceleration or pinging going up hills, and runs well in general. NO hard and fast rules, other than how much total advance (mechanical and initial, only) gets you to approx 36-38 degrees BTDC total.

CBODY67
 
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Tall John has a great series of videos on timing and distributor recurve. He explains how to get your initial and your total cruise. I have no problem with his information. You don't want to just set total mechanical, but if you can't do a recurve that is better then just setting the timing by the fender decal number. As much initial as the engine wants and can take with still being able to start will change the way it idles and wants to go from a stop. Thats when you have to recurve the distributor to not exceed your total and when.

 
Usually, when we talk about total advance, it's for WOT high-rpm situations, somewhat like Nick uses on his dyno pulls. We don't think about what it takes to get there, how emission controls impacted these things, much less vac advance totals.

From the 1950s forward, the racers' orientation was to get "max advance as quick as it can happen", so they could have more power quicker in low gear ff-line. In some extreme cases, even locking the distributor for no-advance, all initial setting. Doing that, they got "consistency", which was important to them in how their engines responded.

In the realm of street driving, many more variables. Still "more and quicker" is better than most OEMs did back then. As they all aimed for that "max advance" optimized number. AND doing it for then-existing octane fuels being used. When I found the SAE paper on the Chrysler 413, for 1958, it was optimized for then-ethyl, which was 97 Research Octane (forget about current Pump Octane, which did not exist back then). IIRC, it stated that 34 degrees BTBC is what it was tuned for on that fuel?

More initial advance always means better off-idle response, but not enough that the total amount does not exceed the 34 degrees BTDC total. Looking at the '66 383 2bbl, it starts at 12.5 BTDC initial. The low-speed advance happens nicely by about 1500rpm, than tapers toward max advance at about 4300rpm, for a total of about 34-36 degrees BTDC. Add the lower rpm advance and the initial and it gets to be about 43.5 degrees BTDC at cruise speeds.

It was discovered that retarding the initial amount of timing helped with CO and HC emissions, so rather than 10 or 12.5 degrees BTDC, the base timing became morel like 5 degrees BTDC, then using the higher rpm advance curve to make up the difference, usually still hitting 34 degrees BTDC (or so) at 4500+ rpm. So, only lower speed performance was affected, while still having full power at WOT rpms.

Less dense mixtures (whether from leanness, part-throttle, elevated altitudes, or combinations thereof) are harder to fire off than a richer (more dense) mixture at WOT, so it takes more "spark lead" to make that happen by the time the piston gets to or near TDC. Which is where the vac advance comes in, to incrementally and variably increase the timing amount as needed. And THAT is where the seemingly wildly-high advance figures come in. Every engine and combustion chamber design has their own "sweet spot" as to how they respond to these things, too.

For example, on the '66 383 2bbl in our Newport Town Sedan, its timing was 12.5 degrees initial. From when we bought it, it liked ethyl/premium fuel better than the regular it was supposed to take, so we used premium as a matter of course. It ran well and had good power and highway fuel economy. I tweaked it a bit up to 15 degrees BTDC, with no problems of any kind. If it was at 12.5, the slisght move to 15 would increase the idle speed. But on my '70 Monaco 383 4bbl (with 906 heard form the factory), when I might increase the initial from 5 degrees BTDC to something a little higher, NO increase in idle speed. I figured that was due to the more-open chamber of the 906s compared to the more-wedge chamber of the earlier models. Never did confirm that, though, just a suspicion.

Typically, vac advance is configured for ported vacuum, which means it is low at idle (lower than the point where the vac advance mechanism is activated) and then approached manifold vac levels once the carb is past the idle system in rpm and air flow. BUT, my investigations concluded that the CARB has to be set-up to use manifold vac for the vac advance rather than ported vacuum. Has to do with where the transition ports in the carb throttle body are in relation to the throttle plates. And all aftermarket carbs are set-up to use ported vacuum for the vac advance, as the vast majority of OEM carbs did or do. These are my experiences in investigating such.

The observed problem with "car advice" is that it can be variable and you have to determine whom is credible and who is not. This can be a big issue, too! And what might have worked for them, from which they extrapolate to mean "always works" might fail with somebody else with a slightly different engine combination. Which is where you have to get a little bit brave and start investigating for yourself, to see what might work and what might not. Tweaks rather than big changes, for example. Against a backdrop of "factory specs for your vehicle".

As to vac and total advance settings, the OEMs have to account for all of those variables in how they set-up the carbs and distributors, plus emissions compliance. So, for some, those factory settings are "too conservative" as they generally work fine for others. This is where tweaking can come in to see if "a little bit better" might be possible.

Driving in hilly areas is different from driving on flat Interstates, too. An engine totally optimized for Interstates might clatter in the hilly areas, for example. So this is where vac advance tuning can come in, with an adjustable vac advance unit. In reality, at this time, I suspect that most of the vac advance units are adjustable, just that we don't know it. As the total advance number might be stamped on the mounting flange, the amount of vac to start and max-out the advance can very from engine to engine, hence the hidden adjustment inside the can. Insert an Allen wrench into the nipple on the vac advance. With a little turning, it should drop into and index with and Allen head socket on the vac advance diaphram center. It should turn to change the spring tension, affecting when things start to happen, as to vac level. Otherwise, as the OEMs used to be, a bradded center of the disphram holder and no adjustment.

I hope this might have explained some things. In any event, use the FSM specs as a starting point/default mode . . . tweaking from there as desired. A digital timing light can be a BIG plus to have, so you can watch these things happen in real time. I bought a dial-back Craftsman timing light years ago, inductive hookup for ease of use, too. It was much better to check things on the car rather than having to use a distributor machine for similar things! It was more expensive than a normal timing light, but well-worth the additional cost for the benefits it provided. And now, we've got digitals!

Take care,
Willis
 
Usually, when we talk about total advance, it's for WOT high-rpm situations, somewhat like Nick uses on his dyno pulls. We don't think about what it takes to get there, how emission controls impacted these things, much less vac advance totals.

From the 1950s forward, the racers' orientation was to get "max advance as quick as it can happen", so they could have more power quicker in low gear ff-line. In some extreme cases, even locking the distributor for no-advance, all initial setting. Doing that, they got "consistency", which was important to them in how their engines responded.

In the realm of street driving, many more variables. Still "more and quicker" is better than most OEMs did back then. As they all aimed for that "max advance" optimized number. AND doing it for then-existing octane fuels being used. When I found the SAE paper on the Chrysler 413, for 1958, it was optimized for then-ethyl, which was 97 Research Octane (forget about current Pump Octane, which did not exist back then). IIRC, it stated that 34 degrees BTBC is what it was tuned for on that fuel?

More initial advance always means better off-idle response, but not enough that the total amount does not exceed the 34 degrees BTDC total. Looking at the '66 383 2bbl, it starts at 12.5 BTDC initial. The low-speed advance happens nicely by about 1500rpm, than tapers toward max advance at about 4300rpm, for a total of about 34-36 degrees BTDC. Add the lower rpm advance and the initial and it gets to be about 43.5 degrees BTDC at cruise speeds.

It was discovered that retarding the initial amount of timing helped with CO and HC emissions, so rather than 10 or 12.5 degrees BTDC, the base timing became morel like 5 degrees BTDC, then using the higher rpm advance curve to make up the difference, usually still hitting 34 degrees BTDC (or so) at 4500+ rpm. So, only lower speed performance was affected, while still having full power at WOT rpms.

Less dense mixtures (whether from leanness, part-throttle, elevated altitudes, or combinations thereof) are harder to fire off than a richer (more dense) mixture at WOT, so it takes more "spark lead" to make that happen by the time the piston gets to or near TDC. Which is where the vac advance comes in, to incrementally and variably increase the timing amount as needed. And THAT is where the seemingly wildly-high advance figures come in. Every engine and combustion chamber design has their own "sweet spot" as to how they respond to these things, too.

For example, on the '66 383 2bbl in our Newport Town Sedan, its timing was 12.5 degrees initial. From when we bought it, it liked ethyl/premium fuel better than the regular it was supposed to take, so we used premium as a matter of course. It ran well and had good power and highway fuel economy. I tweaked it a bit up to 15 degrees BTDC, with no problems of any kind. If it was at 12.5, the slisght move to 15 would increase the idle speed. But on my '70 Monaco 383 4bbl (with 906 heard form the factory), when I might increase the initial from 5 degrees BTDC to something a little higher, NO increase in idle speed. I figured that was due to the more-open chamber of the 906s compared to the more-wedge chamber of the earlier models. Never did confirm that, though, just a suspicion.

Typically, vac advance is configured for ported vacuum, which means it is low at idle (lower than the point where the vac advance mechanism is activated) and then approached manifold vac levels once the carb is past the idle system in rpm and air flow. BUT, my investigations concluded that the CARB has to be set-up to use manifold vac for the vac advance rather than ported vacuum. Has to do with where the transition ports in the carb throttle body are in relation to the throttle plates. And all aftermarket carbs are set-up to use ported vacuum for the vac advance, as the vast majority of OEM carbs did or do. These are my experiences in investigating such.

The observed problem with "car advice" is that it can be variable and you have to determine whom is credible and who is not. This can be a big issue, too! And what might have worked for them, from which they extrapolate to mean "always works" might fail with somebody else with a slightly different engine combination. Which is where you have to get a little bit brave and start investigating for yourself, to see what might work and what might not. Tweaks rather than big changes, for example. Against a backdrop of "factory specs for your vehicle".

As to vac and total advance settings, the OEMs have to account for all of those variables in how they set-up the carbs and distributors, plus emissions compliance. So, for some, those factory settings are "too conservative" as they generally work fine for others. This is where tweaking can come in to see if "a little bit better" might be possible.

Driving in hilly areas is different from driving on flat Interstates, too. An engine totally optimized for Interstates might clatter in the hilly areas, for example. So this is where vac advance tuning can come in, with an adjustable vac advance unit. In reality, at this time, I suspect that most of the vac advance units are adjustable, just that we don't know it. As the total advance number might be stamped on the mounting flange, the amount of vac to start and max-out the advance can very from engine to engine, hence the hidden adjustment inside the can. Insert an Allen wrench into the nipple on the vac advance. With a little turning, it should drop into and index with and Allen head socket on the vac advance diaphram center. It should turn to change the spring tension, affecting when things start to happen, as to vac level. Otherwise, as the OEMs used to be, a bradded center of the disphram holder and no adjustment.

I hope this might have explained some things. In any event, use the FSM specs as a starting point/default mode . . . tweaking from there as desired. A digital timing light can be a BIG plus to have, so you can watch these things happen in real time. I bought a dial-back Craftsman timing light years ago, inductive hookup for ease of use, too. It was much better to check things on the car rather than having to use a distributor machine for similar things! It was more expensive than a normal timing light, but well-worth the additional cost for the benefits it provided. And now, we've got digitals!

Take care,
Willis
Thanks for the info Willis. Just got back from my mechanic. His employee had a $600 digital Snap On timing light. I half jokingly asked if I could borrow it and got a resounding "NO". But I was watching Vice Grip Garage on You Tube and that fellow Derrick uses an "ear O'meter" to time his engines (that is he listens to it). Wonder what the difference in performance would be between an experienced ear and a $600 tool. Paul
 
also, to further confuse things...hotter cams with more overlap can have trouble maintaining a decent idle and need more initial advance to compensate...so there are advance limiting plates available for stock distributors so you can set them up at a higher initial setting without them exceeding the recommended total advance....the reason i'm mentioning this is because you have a MSD distributor...which being a performance unit may have a shorter mechanical curve than a stock unit, lighter springs to get the advance in more quickly, and possibly an adjustable vacuum unit that has different specs than stock...so the first thing you need to do is contact MSD and find out exactly what the specs are on your distributor so you can figure out where to set it and if you need to change springs or anything to possibly make it more streetable.
 
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A few qualifiers . . . . at what duration @ .050" lift does "hotter cam" mean. AND at what lobe separation??? Are we talking about another 30 degrees duration with a bit more lift to complement that (which many times means a 110 degree lobe separation, rather than the more-OEM 114 degrees, or even 112 degrees? Or the old hot rod cams with over 300 degrees advertised duration, from the 1960s? Cams which need 3000rpm to not die when the clutch is popped?

Certainly, any "larger cam" will need more air to idle, just idle when warm, so the primary throttle plates will need to be open more. If such additional opening is too large, with an off-idle flat-spot of big sag, then the throttle plates need to have an air hole drilled in them, so they can be closed back to OEM levels and get rid of that off-idle issue.

Through all of this, the engine's spark map might change a bit, even needing LESS advance for best power, as the cylinders will be getting MORE charge in them than before. Like maybe 34 degrees total rather than 36-38 degrees total? A variable situation, as long as the engine does not clatter at WOT.

Some of the older hot rodder engine tuners would take the distributor apart, braze teh advance slots shorter, then reassemble with lighter springs to get all of the advance happening by about 2000rpm, or thereabouts. Had nothing to do with any lack of lower rpm torque from the big cam, just getting all of the advance in as soon as possible. Seems like most also figured on a 12 degrees BTC initial timing, for good starting, too? Full mechanical, too. Vac advance removed.

An engine so tuned probably had at least 3.73 gears, too, with a manual transmission, and was not used for extended highway cruises. Not because of the tuning, but because of the deeper gears and non-OD transmission. THAT customer was prepared to pay for that set-up being "race oriented", for various rasons, too.

Now, we used to talk about when an engine got "on the cam", which meant that the cam was working to fill the cylinders with charge better past a certain rpm, with a certain cam/carb/ignition/cyl head/exh system set-up. For example, on my '70 Monaco 383 "N", with 3.23 gears and H78-15 tires, that happened at 62mph. Below that, the throttle response was slightly soggy, but from 62mph and higher, the throttle response was very "tight" and the least input resulted in higher cruising speeds immediately, not a second or so later (as it did below 62mph). This with a factory hot base initial timing of 5 degree BTDC.

So you have to look at the distributor calibration as a comprehensive deal. In comparing the 1966 383 2bbl distributor curves to a 1970 383 4bbl curves, the '66 used 12.5 degrees BTDC whereas the '70 4bbl used 5 degrees BTDC. But by the time they got to 4500rpm, the total advance (base + mechanical) was pretty much 34-36 degrees BRC total. So it starts with if you start with a lot and gain a little bit higher in the rpm range, or start with less and gain it over 2000rpm. The '66 motor had the old 252/.390" cam as the '70 had the 256/260 cam and HP exhaust manifolds, from the factory.

The reason I mentioned the lobe separation angle was that when I upgraded my '77 Camaro 305 2bbl to a 4bbl and 210 @ .050 cam w/.440" iift, with the stock advance curve, the car was underwhelming i how it ran, to me. So I was tweaking and such to get the advance in quicker, by 3000rpm or so. I'm not sure it got to be more optimized, but it was good enough for daily use. The base spec for the timing was 4 degrees BTDC, but I later discovered that it came out of the factory at 8 degrees BTDC. And that is pretty much where it is now, to keep from pinging on super unleaded gas. That cam was at 110 degrees, which affected idle quality in gear. BTAIM

So, from what I've seen, there can well be some generalities, but one combination that works for one engine set-up might not be the best one for another engine, for various reasons. As they might say . . . "Additional tweaking required for best results."

Sorry for the length,
CBODY67
 
A few qualifiers . . . . at what duration @ .050" lift does "hotter cam" mean. AND at what lobe separation??? Are we talking about another 30 degrees duration with a bit more lift to complement that (which many times means a 110 degree lobe separation, rather than the more-OEM 114 degrees, or even 112 degrees? Or the old hot rod cams with over 300 degrees advertised duration, from the 1960s? Cams which need 3000rpm to not die when the clutch is popped?
....
So, from what I've seen, there can well be some generalities, but one combination that works for one engine set-up might not be the best one for another engine, for various reasons. As they might say . . . "Additional tweaking required for best results."

Sorry for the length,
CBODY67
WISE WORDS! I've recently twiddled a points distributor meant originally for a 2 bbl 1966 engine, putting some nice old Blue Point springs into it for SNAP!, then using a limiter plate to hold it to 10 degrees mech advance. The vacuum advance is 9.5 degrees. I've set the initial advance up to the canonical 1966 2 barrel one, 12.5 BTDC. While some would think this setup absurdly conservative with the nice Edelbrock Performer 1405 carb now on this old engine, it runs better now than it ever did in the previous 6 years. I think adding the 1/2 inch insulating spacer has helped give a mite more plenum volume for the intake mixture too.

NOW, I REALLY have to keep my foot lighter on takeoffs, as it does plenty of "scratch" with the little 14" stock wheels and a 3:23 rear end. My next bolt on enhancement will be to put the dual exhaust back on this motor, and maybe even a HP exhaust manifold for the passenger side with that. I stuck w closed qurnch heads too, using the 915s I had milled for this motor. It has all come together very nicely. I think I'll also set the limiter up a notch. and see if it gets any snappier. So far, its all been good.
 
Thanks for the info Willis. Just got back from my mechanic. His employee had a $600 digital Snap On timing light. I half jokingly asked if I could borrow it and got a resounding "NO". But I was watching Vice Grip Garage on You Tube and that fellow Derrick uses an "ear O'meter" to time his engines (that is he listens to it). Wonder what the difference in performance would be between an experienced ear and a $600 tool. Paul
Typically, "timing by ear" can result in too much advance, ending up with retarding the setting to kill part-throttle pinging on acceleration or going up hills. Some people drive easy and others don't . . . many variables, even altitude.

Now, some "more vintage" mechanics know what to listen for in such "by ear" methods, but many who claim to know probably do not know. Hence, the "over-advance" result, from what I have seen. End result, break out the timing light to see where things are.

To do the "by ear" procedure "right", the rpm needs to be at 4000rpm or so, when the distributor mechanical advance is near its max, rather than at 2000rpm (unless the springs have been lightened). I don't know too many people willing to be hanging over the side of a fender at 4000rpm, then or now.

Rather than the modern advance-limit plates (to limit mechanical advance), the slots were brazed shorter with a torch, making the slots shorter. How they determined the resultant length, accurately, never was disclosed. Similar with vac advance cans, too.

Just some observations,
CBODY67
 
Typically, "timing by ear" can result in too much advance, ending up with retarding the setting to kill part-throttle pinging on acceleration or going up hills. Some people drive easy and others don't . . . many variables, even altitude.

Now, some "more vintage" mechanics know what to listen for in such "by ear" methods, but many who claim to know probably do not know. ....

Just some observations,
CBODY67

As a youth, ears were all I owned for timing, but I learned to twiddle my Fords alright, after a few minor disasters. There were many more "Old Timers" around in those daze to "help" with such. From them, I learned to rely on myself, and generally draw iron on anyone offering help..... Sometimes, malicious and/or ignorant advice can teach valuable lessons.

Lesson 1: GET A TIMING LIGHT!
 
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