1BAD71455

I have a 455 that I changed back to points from pertronix. I installed a fresh distributor with accel 23 oz. points gapped to .016 and I have it timed just right and then I plug in the vacuum advance and I get pinging under medium to heavy acceleration. I know my carb isn't perfectly tuned, but it is a fresh rebuild with the engine less than 2000 miles ago. Carb tuning should be after timing anyway. Any guidance will be appreciated. MSD blaster 2 coil with stock setup and mild cam (e977p). R45S AC Delco Plugs. wanting to replace with ngk 2746 after timing is done.
Steve

oldcutlass

First thing, you either need to use the stock resistor wire or a ballast resistor with the points. You can't run points with a full 12v. The .016 point gap gets you close, but you need a dwell of 30.

Your total mechanical timing goal is 36 deg BTDC @ 2800-3000 rpm with vacuum advance disconnected. With it connected you want your total to be around 46 - 50 with no pinging.

The sticking point is the amount of mechanical advance available on a points type distributor, so you may have to limit it to get a higher initial setting for mildly modified engines.

MDchanic

Yeah, you need to tune your timing now that you've modified the motor.

I would recommend a Crane Cams kit for the purpose, with a variety of advance springs and an adjustable vacuum can.

First you have to get your maximum mechanical advance tuned in, to about 36° at about 3,000 - 3,500 RPM (the exact best choice will vary),
Then you have to make sure the low-RPM end of the centrifugal advance is adjusted, that is, that your car will start easily, and that the timing isn't varying with RPM below about 1,000, because if it is, your idle may wander.
Next, you have to check your full-throttle timing through the RPM range - you may need to swap springs if you find you have a spot where it pings.
Finally, you have to tune in your part-throttle vacuum advance, using the adjustable can and a dash-mounted vacuum gauge, so you have some clue as to what's going on.

I've posted about this in the recent past, so you can probably find it by searching.

- Eric

1BAD71455

Thanks guys, I have never enjoyed the finer points of tuning my car. I have learned a lot of things about the steps taken to get the beast to run as smooth and powerful as possible. I will continue until I succeed. I thought I set it right last night until I plugged in the vaccuum line and it was pinging again. unplug and it runs like a raped ape. I think I need the timing tape for the balancer also.

oldcutlass

You need a dial back timing light and an adjustable vacuum advance canister. What you need to do is see where your total timing is @3000 rpm with vacuum advance connected and go from there. The goal is to be no more than 50 deg btdc. Like I said in my earlier post, if your also trying to get a lot of initial timing then you are going to exceed the amount of total mechanical timing at your upper rpm limits. You may have to install a mechanical stop, it all works hand in hand.

Sampson

I am planning on installing a pertronix ignition. Why are you removing yours? Good luck with your tuning

MDchanic

Too much vacuum advance.
Start with an adjustable unit, and bring it up gradually.
What is the number on the unit you are using now?



If you e-mail me, I can send you a .pdf of one that I made.
If you just want to make marks on your balancer, then measuring from TDC,
20°=28.8mm
30°=43.3mm
35°=50.5mm
40°=57.7mm
50°=72.1mm

- Eric

1BAD71455

Sampson, I trusted one person to install the pertronix unit and the magnet ring ended up touching the ignitor unit and it lost two magnets. I didn't want to try a third time. I put in a fresh reman distributor with 23 oz HD accel points. KISS for now. Just a stock A1 Cardone reman unit & stock vacuum can. Thanks for the input oldcutlass. I am starting to think my stock springs in the dist. are as lame as the stock points they put in them. I am buying a dwell meter cheap today and gettin this beast screamin.

oldcutlass

As Eric stated invest in an adjustable vacuum canister also. You will thank us later.

64Rocket

are you using ported vacuum or manifold vacuum ?

You should use ported, at idle there should be no vac advance, only at off idle.

Gene

MDchanic

I believe that his engine is modified, so that may or may not be true.

Also, it wouldn't affect the problem he's talking about.

- Eric

Octania

I found that the ported vacuum was a disaster for the 403 with shaved 6 heads, and 290? cam... would not behave at idle, then if you retard the timing to factory specs, overheated....

Mech. Adv. Kit
Adj. VA can set to 10-11 degrees
full manifold vacuum to the dist'r
a bit of learning on how to measure and set VA and MA
several test runs at different settings

Now MUCH better.

PS there is no such thing as "a" stock VA canister.
There are DOZENS and DOZENS of different ones, with various starting vacuum levels, various all-in vacuum levels, and various total travel figures.

Octania

http://www.engine-restoration.com/re.../Timing101.pdf
See also http://www.britishv8.org/Articles/Me...gn-Advance.htm
And, for parts: http://www.parts123.com/parts123/yb....fib~~~~A30~A21
FELT WASHER Item# 271023 for 1956-1974 $1.95
……………………………………………….
DISTRIBUTOR LEAD WIRE GROMMET, Item# 271022 for 1958-1974, $1.95
………………………………………………..
DISTRIBUTOR SMALL PART KIT
Item# 272149 for 1957-1974, $8.95
Felt washer, plastic seal, lead wire grommet, pin, screws
NOTE that one buyer advises to order the plastic seal separately because the one in the kit differs slightly. http://www.v8buick.com/archive/index.php/t-238883.html
………………………………………………..
DISTRIBUTOR SHAFT BUSHING SET - UPPER AND LOWER
Item# 272160 for 1962-1974, $17.95
.++++++++++++++++++++++++++++++++
DISTRIBUTOR SPRING AND WEIGHT KIT
Item# 271027 for pts type 1956-1974, $18.95
………………………………………………..
DISTRIBUTOR BUSHING INSTALLATION TOOL
Item# 272161 for 1962-1974, $8.95
………………………………………………..

Octania

by the way this was a COMPLETE PITA to retrieve and enter here piece by piece so SAVE IT in your computer please!

TIMING AND VACUUM ADVANCE 101
By John Hinckley
In this day and age, when modern automotive powertrains are computer- ontrolled and engines don’t even HAVE distributors any more, the knowledge of what distributors did and how they operated to control ignition timing has begun to fade; for those just entering the classic automotive hobby, the function of the distributor and the notion of “timing” is even more mysterious. To keep your classic engine running reliably and at maximum efficiency, some knowledge about the principles of spark timing and how it’s controlled is essential. The objective of this article is to demystify the principles of “spark timing”, and to explain why and how your distributor-equipped Engine’s spark timing is controlled and varied to suit changing driving conditions. I won’t get into the gory details of combustion theory, but let’s understand a little about what happens as the piston is traveling upward on the compression stroke toward the point where the spark plug “lights the fire”. Before we light the fire, let’s talk a little about what we’re lighting – the fuel-air mixture that’s been metered by the carburetor and atomized in the intake manifold as it heads for each cylinder’s intake valve.
Fuel/Air Mixture and “Burn Rate”: At idle and steady cruising speed, the load on the engine is low, and the air-fuel mixture is “lean” (more air/less fuel); when accelerating, the load on the engine is higher, and it’s fed a “rich” air-fuel mixture (more fuel/less air). These are two very different conditions, as a lean mixture burns relatively slowly, and a rich mixture burns faster. Remember this distinction – it’s a key factor in ignition timing.

Back in the cylinder, with the piston rising and compressing the air-fuel mixture, the idea is to fire the spark plug at just the right moment such that the mixture is ignited (starting the “burn”, as the flame front proceeds across the cylinder) and the rapidly-expanding gases reach peak cylinder pressure just after the piston reaches TDC (top dead center), exerting maximum force to push the piston down on the power stroke for maximum efficiency.

Spark Timing: Referring back to the burn rate comparison, slower-burning lean mixtures need to have the “fire lit” earlier in the compression stroke (because they take longer to reach peak cylinder pressure) than faster-burning rich mixtures (which take less time to reach peak cylinder pressure). With either mixture condition, the objective is to reach peak cylinder pressure at exactly the same point after TDC, which says they have to be “lit” at different points during the piston’s upward travel – this is what “spark timing” is all about – managing the point at which the spark plug fires under different operating conditions. This point is expressed as “spark advance,” in degrees of crankshaft rotation before the piston reaches top dead center; when someone says their initial timing is set at 10 degrees, that means the distributor is set to fire the spark plugs when the crankshaft is 10 degrees of rotation before the piston reaches top dead center, which is “10 degrees of advance”. This is the “initial” or “base” spark timing which is checked and set at idle during a traditional tune-up (with the vacuum advance disconnected); it’s fixed at the point where it’s set by clamping down the distributor hold-down bolt, and doesn’t change – it’s always there.

Early Spark Timing: In the days of the simple, low-compression, inefficient Model T, spark advance was set manually to a fixed level with a lever on the steering column; about all the driver did was to “retard” (delay) the spark timing while turning the crank to start the engine, then move the lever to “advance” the spark timing once the engine was running. If the driver forgot to retard the spark when cranking and left the lever in the advanced position, the engine could “kick back” while the operator turned the crank to start the engine, which could result in a broken arm (an unforgettable lesson in spark timing). Once running, the operator could vary the spark advance with the lever for best performance (such as it was), or just leave it alone (which most operators chose to do). With that big, low-compression, slow-running, low-powered engine, little damage could be done by improperly setting the spark advance.
Fast-forward to the 1960’s and high-compression 350-horsepower W31 engines howling at 6500 rpm; suddenly the spark timing equation is much more complex, and spark timing errors can result in scattering expensive engine parts all over the street at one extreme, and poor performance and fuel economy at the other extreme. An automatic device has to recognize the entire spectrum of operating conditions and manage the complexities of spark timing in a manner completely independent of, and transparent to, the driver, who has other things to keep him occupied – like traffic, flashing blue lights in his mirrors, etc.

The Distributor & Advance: This wondrous device that handles all that work is the distributor, which lives quietly in the dark, at the back of the engine, hidden forever under the engine’s ignition shielding, demanding only an occasional set of points, a condenser, and cap & rotor to continue doing its job. Let’s talk about the two different ways the distributor manages spark timing while you’re watching traffic and grabbing gears – centrifugal advance and vacuum advance.

The centrifugal advance mechanism under the rotor in the distributor advances spark timing based solely on engine rpm (it’s driven at half crankshaft speed); a pair of weights pivot on pins, and are retained by little coil springs. The faster the shaft turns, the more the weights tend to pivot outward (centrifugal force), and the rate at which they move outward is controlled by the tension of the little springs; lighter springs let them move fully outward at relatively low shaft rpm, and stronger springs require higher shaft rpm for full outward movement. The pointed “tail” of the weights, at the pivot end, bear against a cam (called the “autocam”) attached to the top of the distributor shaft, and as the weights move outward, the 8-sided cam that opens and closes the contact points (which trigger the coil to fire the spark plugs when the points open) is “advanced” so it opens the points earlier than when the weights are fully retracted (as they are at idle). In most distributors, this mechanism provides up to 20-25 (crankshaft) degrees of spark advance when the weights are fully extended; the maximum advance this system can provide is limited by a bushing installed over a pin which moves in a slot in the lower plate of the autocam. The system is designed so that the weights don’t begin to move until slightly above normal idle rpm, so the initial timing can be set accurately without any influence from the centrifugal advance mechanism.
[continued]

Octania

Centrifugal Advance Calibrations: There are many different calibrations of weight configurations and spring tensions specified for production Engine distributors, depending on the performance level of the engine, manual or automatic transmission, etc. The points between the rpm at which the weights begin to move and the rpm at which they’re fully extended, providing maximum advance, is referred to as the “centrifugal advance curve”, which is tailored to each engine combination. The key point to remember here is that the centrifugal advance mechanism advances and retards spark timing in response only to engine rpm, and nothing else. Its function is to advance spark timing as engine rpm increases; as upward piston speed increases with rpm, effectively shortening the time for the compression stroke, the spark has to fire sooner, as the air/fuel mixture still takes the same amount of time to burn as it does at lower rpm. In effect, the centrifugal advance mechanism handles only the basic physics of lighting the fire sooner at higher rpm so peak cylinder pressure is still reached at the same point just after TDC.

Now we have the basic physics handled, but we still need another system to manage spark advance based on all the variations of driving conditions and engine load variations experienced in normal operation; this is handled by the vacuum advance system.

Vacuum Advance: The vacuum advance system consists of a vacuum diaphragm mounted on the distributor body; the diaphragm is spring-loaded in the zero-advance position, and has a rod which connects to a hole in the breaker plate, which is the movable plate the points are mounted on. When vacuum is applied to the diaphragm, it pulls on the rod, which in turn pulls on the breaker plate, rotating it with respect to the 8-sided cam on the distributor shaft which opens and closes the points. When viewed from the top, the distributor shaft (and the 8-sided cam for the points) of your Oldsmobile V8 turns counter-clockwise; when the vacuum advance rod pulls on the breaker plate, it rotates the breaker plate (and the points) clockwise, which “advances” the opening of the points which triggers the coil to fire the spark plugs). A typical vacuum advance unit, when fully deployed, will add about 15 (crankshaft) degrees of spark advance over and above what the distributor’s centrifugal advance system is providing at the moment, which depends only on engine rpm; they are two independent systems, but they work together to provide the correct amount of spark advance for the engine’s current operating conditions. Factory vacuum advance units will have some numbers stamped into the steel frame- such as “468 20” – The final 3 digits of the GM part number 1973468, and the crank degrees of advance it can offer- 20 degrees.

Controlling Vacuum Advance: Let’s look at how the vacuum advance system is controlled. Referring back again to burn rates, remember that lean mixtures burn slower, and rich mixtures burn faster. Engine load conditions (idle, steady cruise, acceleration) result in how lean or rich the air/fuel mixture is (the carburetor handles this), and the best indicator of engine load is intake manifold vacuum. At idle and steady cruise, engine load is low, and intake manifold vacuum is high due to the nearly-closed carburetor throttle plates; under acceleration, the throttle plates open wider, and intake manifold vacuum drops; it is essentially zero at wide-open throttle. As a result, intake manifold vacuum is a “free” indicator of engine load, which correlates nicely with fuel mixture being supplied – lean mixture at high vacuum, and rich mixture at low vacuum. At idle, the engine needs additional spark advance in order to fire the lean (and exhaust-diluted) idle fuel/air mixture earlier in the cycle in order to develop maximum cylinder pressure at the proper point after TDC for efficiency, so the vacuum advance unit is activated by the high manifold vacuum, and adds another 15 degrees or so of spark advance on top of the fixed initial timing setting. For example, if your initial timing is set at 10 degrees, at idle it’s actually 25 degrees with the vacuum advance connected (a properly-calibrated centrifugal advance mechanism will not have started to move yet at idle rpm).

The same thing occurs under steady highway cruise conditions; the mixture is lean, takes longer to burn, the load on the engine is low (it only takes about 40 horsepower to cruise at 50mph) and the manifold vacuum is high, so the vacuum advance unit is again deployed, and adds 15 degrees of spark advance over and above whatever the distributor centrifugal advance mechanism is providing at that engine rpm. If you had a timing light connected so you could see it as you cruise down the highway, you’d see about 45-50 degrees of spark advance; your fixed initial advance of 10 degrees, 20-25 degrees provided by the centrifugal advance mechanism, and the 15 degrees added by the vacuum advance unit. [Continued]

Octania

When you accelerate, the fuel/air mixture is immediately enriched (by the accelerator pump, power valve, metering rod piston, etc.), and that rich mixture now burns faster, doesn’t need the additional spark advance any more, and when the throttle plates open, the manifold vacuum drops, and the vacuum advance unit diaphragm retracts to its zero position, “retarding” the spark timing back to what is being provided at that moment by the fixed initial timing and the centrifugal advance mechanism. The vacuum advance doesn’t come back into play until you back off the pedal and thus manifold vacuum increases again as you return to steady-state cruise; now the mixture again becomes lean and needs the additional vacuum based spark advance for optimal fuel efficiency.

Vacuum Advance Calibration: There are also many different calibrations of vacuum advance units; some begin to deploy at different vacuum levels than others, and some provide more degrees of advance when fully deployed than others. The original calibration was selected based on the intake manifold vacuum characteristics of that particular engine/transmission combination and how it was expected to perform in daily use. Vacuum advance units were connected to full manifold vacuum for decades; in the late 60’s and early 70’s, when emissions began to become an issue, many were instead connected to “ported” or “timed” vacuum sources. We’ll discuss this aberration a little later.

The Advance Combination: Now we have two different advance systems working independently, but complementing each other, to manage spark timing – centrifugal, based on engine rpm, and vacuum, based on engine load and operating conditions. The centrifugal advance system is purely mechanical and is only rpm-sensitive; nothing changes it except engine rpm. Vacuum advance, on the other hand, responds instantly to engine load and rapidly-changing operating conditions, providing the correct amount of spark advance at any point in time, to deal with both lean and rich mixture conditions.

By today’s computerized engine management terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely zero negative effect on wide-open throttle performance, as the vacuum advance is inoperative under that condition. In modern cars with computerized engine controllers, all those sensor inputs to the computer change both spark timing and fuel/air mixture 50 to 100 times per second, and we don’t even have a distributor any more – it’s all electronic.

“Ported” Vacuum: Now to the widely-misunderstood manifold-vs.-”ported” vacuum aberration. After 30-plus years of controlling vacuum advance systems with full manifold vacuum, that “free” indicator of engine load and fuel mixture, along came early emission control requirements (seven years before catalytic converter technology was introduced), and all manner of crude band-aid systems were introduced to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these crude, but effective systems was GM’s Air Injection Reactor (A.I.R.) system, which pumped fresh air into the exhaust ports to “afterburn” pollutants in the exhaust manifolds. The key to making this system work at maximum efficiency was retarded spark at idle; with retarded idle spark timing, the “burn” begins late, and is not complete when the exhaust valve opens, which does two important emissions-related things. The incomplete burn reduced combustion chamber temperatures, which reduced the formation of oxides of nitrogen (NOX), and the significant increase in exhaust gas temperature ensured rapid light-off and combustion of the hydrocarbons in the exhaust gas stream when the fresh oxygen-carrying air was introduced from the air pump.

Side Effects: As a result, these engines ran poorly, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to “run hot” at idle; cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it. “Ported Vacuum” was easy to implement – they just moved the distributor vacuum port orifice in the carburetor from below the throttle plate (where it was exposed to full manifold vacuum) to above the throttle plate, where it was only exposed to manifold vacuum after the throttle plate opened. This meant that the vacuum advance was inoperative at idle (retarding idle spark timing from its optimum value), and these applications also had very low initial timing settings; they were usually set at 4 degrees before TDC or less, and some even had initial timing settings as much as 2 degrees after TDC. The vacuum advance still worked at highway cruise, but not at idle; this arrangement caused all manner of problems. “Ported Vacuum” was strictly an early pre-converter crude emissions strategy, and nothing more. Don’t believe anyone who tells you that ported vacuum is a good thing for performance and drivability – it’s not. Anyone with a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don’t understand what vacuum advance is, how it works, and what it’s for. There are lots of long-time experienced mechanics who don’t understand the principles and operation of vacuum advance either, so they’re not alone.

Summary: Now that we’ve covered the whys and hows of spark timing and its control systems, you can appreciate what’s going on underneath your ignition shielding and how it affects performance and drivability. Checking the operation of the centrifugal and vacuum advance systems during periodic maintenance and tune-ups can pay real dividends that you can feel in the seat of your pants. [End]

Erinyes

Excellent article, Octania. It is now safely on my computer :-)

Sadly, the first link, to www.engine-restoration.com, isn't working for me. Closest I can find is http://enginerestoration.com/, which doesn't appear to have anything like the article you posted.

1BAD71455

Thanks a lot octania. I had to go to the doctor for my back pain. Not able to work on my car for 5 days now. I have the crane came adjustable vac can & spring kit. I guess my body isn't 20 any more.
Thanks to everyone else for the info. I will be running smooth by Friday.

oldcutlass

I found this out last Sunday also. Hope you get back on your feet soon.

Sampson

There is a lot of great info on this thread. Eric, Eric and Octania, thanks for the input. I have been blindly tuning my cars for a lot of years and through trial and error would get to where I wanted to be. After reading this thread I'll bet I get it tuned a lot closer and faster. I learn something new everyday

MDchanic

You're welcome. I think I can say that we're all glad to help out and keep another Olds on the road and running well.

- Eric

Octania

x2 what MDchanic said
Trying to polish this turd of an interweb into a semi-useful place to get pertinent facts or at least real life experiences that others can use to their advantage.... w/o bickering, bitching and BULLSHED.

oldcutlass

X3 especially w/o bickering, bitching and BULLSHED!

MDchanic

Yeah. It's fun to argue, but we try to avoid the dumb@$$ childish crap.

We sometimes get picky, but it's because we try to present information that is factually reliable, not that "I read it on the internet" crap.

- Eric

1BAD71455

Crane cams adjustable vac can and springs are installed and working great. Thanks guys for all the info. just went over 2600 miles on new engine. I forgot how fast she gets up to 80. Initial+mechanical+vacuum I get it now. I love the roar when the secondaries kick in.

MDchanic

Great! Glad you got it sorted out!

- Eric

oldcutlass

X2!!