Close



Results 1 to 15 of 15
  1. #1

    Default The Ultimate Duraspark Distributor Timing Guide.

    This is an article I have put together from many sources.

    I hope it answers all of your Duraspark Timing and Tuning questions.

    Lets start at the beginning......

    Maybe you've just built up a brand new engine, or upgraded to new heads and a cam, perhaps you're simply trying to dial-in an existing combination. In either scenario, one area of tuning that is highly overlooked and greatly misunderstood is timing. All too often we see people dropping in their distributor, making a quick adjustment with their timing light, and setting off to make another pass.

    Timing is everything, and without a proper timing curve, every thing else goes out the window. Jetting changes, fuel pressure adjustments, are all useless if first the timing is not set correctly.


    So what is timing? In a nutshell, timing or 'ignition timing' relates to when the sparkplug is fired in relation to piston position. At idle, when engine speeds are the lowest, the plug fires just before the piston reaches the top of its stroke. As engine speeds increase, the time between piston strokes is less, and therefore the plug must fire sooner. In all cases the plug is fired in advance of the piston reaching top dead center. There is a small window of time in which the combustion need to take place in order to produce peak power. Too late and power is lost, too soon and detonation occurs, which can lead to melted pistons.

    Why an engine needs more advance as its speed increases.
    When the compressed mixture inside a cylinder is ignited it takes time for the flame front to reach the piston and for the expanding gases to start pushing it down. The time that this takes changes according to a number of variables such as mixture strength, how well the cylinder has filled (dependent on volumetric efficiency and throttle opening), compression ratio and combustion chamber shape. Given the same circumstances of mixture strength, cylinder filling and CR, the time taken for the mixture to fully ignite and burn is the same regardless of engine speed. At increasingly higher RPM however, the time available for this burn to take place is correspondingly less, so it follows that you have to start burning the mixture earlier in order for it to push on the piston at the right time. This is the basis for increasing ignition advance.
    Too much of this and the burning mixture hits the piston as it rises (pinking or pinging), too little and the flame front reaches the piston far too late and does not do a good job of pushing the piston down and the engine behaves like a herd of turtles. One of the reasons a diesel engine does not perform at higher RPM is that it has compression only ignition, so there is no way to increase the effective ignition advance.
    How this is achieved
    The distributor as fitted to conventional ignition systems does not just distribute the spark amongst the cylinders and switch the coil; it also contains a centrifugal mechanism that advances the ignition timing automatically as engine RPM rises. Normally there are a pair of weights within the distributor which under the affects of centrifugal force tend to be thrown outwards, this tendency is greater as RPM increases. The weights are shackled by two small springs that restrain them progressively. As the weights move outwards they exert a turning force on the top of the distributor shaft relative to the driven part of the shaft, this moves in the same direction as the distributors rotation thereby causing the points/electronic trigger to actuate earlier and advancing the ignition timing. As engine speed increases the weights overcome more of the spring's tension and advance the timing still more. There is normally a stop of some kind that limits the amount of advance that the distributor can supply. This centrifugal mechanism is usually hidden away underneath the baseplate of the distributor.


    In this article we're going to focus primarily on carburated, non-computer controlled, engines which have fully adjustable distributors. The EEC-IV computer controlled Fords allow for setting initial timing, but the rest is adjusted by the computer. The newer modular engine Fords have distributor-less ignitions which offer no adjustability from the factory, although companies like Steeda have recently developed timing adjusters for these engines. Some Fords, particularly in the 70's and early 80's, had distributors where timing was fixed due to emissions reasons.

    When it comes to timing the most common myth is that adjusting the timing simply means moving the distributor clockwise or counterclockwise. While this does affect the timing, it is not the correct way to adjust the timing curve. To explain why, we first we need to define some terms.

    Advancing and retarding timing refers to increasing or decreasing the 'time' at which spark is delivered to the cylinders. This 'time' is measured in crankshaft degrees, signified by marks on the harmonic balancer, and a reference pointer on the block or timing chain cover. When the piston is at Top Dead Center (TDC), this is synonymous with zero degrees on the balancer. Ten degrees before that point would mean the piston is ten degrees of rotation from being at TDC.

    So how does the crank position relate to the distributor?
    The distributor shaft on Ford engines is driven by the camshaft gear, which is turned at half-crank speed by the timing chain connected to the crankshaft. Thus there is a direct correlation between the position of the crank and the position of the distributor. Remember, the distributor is a switch. Regardless of the type of distributor you have, there is a fundamental design common to all of them; the shaft is in a fixed position, spinning in direct relation to the crankshaft. On the shaft sits the trigger which activates the switch. On electronic distributors the trigger may be a magnetic sleeve with eight openings, or in the case of points, its simply an arm that open and closes the points. The distributor housing does not spin and it contains the actual switch, such as the Pertronix box, which is mounted on a breaker plate. By rotating the housing you in effect move the position of the switch, changing when it triggers a spark. When you rotate the distributor to "adjust the timing" you are moving the switch on the housing side in relation to the trigger on the shaft.

    Rotating the distributor housing clockwise on a Ford advances the timing (i.e. spark is being fired a greater number of degrees before the piston reaches TDC), and counterclockwise decreases the timing.

    When referring to timing, there are really four terms that must be considered; initial timing, mechanical (or centrifugal) timing, total timing, and vacuum advance. There is also cam timing which is more appropriately termed valve timing, since it deals with when the valves open and close in relation to crank position. We won't talk about this since it has no dynamic bearing on ignition timing.

    Initial: This is the most common adjustment that people associate with timing. At idle, with the vacuum advance hose disconnected and plugged, this is the timing that you would see if you flashed timing light on the timing marks. On typical stock engines you'd see as low as 0 to as high as 15 degrees. Most Ford shop manuals specify around 6-8 degrees initial timing advance for the 289-351 motors.

    Mechanical/Centrifugal: Most V8 distributors contain an internal advance mechanism consisting of two each of weights, springs, and slotted 'reluctor' arms. There is also a stop tab for the arms. On Fords this assembly can only be seen by removing the cap, rotor, and breaker plate; we'll get to removal a bit later. As the distributor shaft spins with increasing rpms, the centrifugal force acts on the weights, which begin to force outwards against the springs. This movement rotates the shaft and thus advances the timing. The slotted arm controls how much the weights can move the assembly, and the springs control how fast the assembly reaches that limit. The reluctor arm on a Ford has two slotted sides, only one side contributes to the timing, the arm can be flipped around if more advance is needed (see pictures.) On Fords each side is stamped with a number, usually 10L and 13L; or some have 15L and 18L. These numbers refer to 1/2 of the total degrees of timing that will be obtained when using that arm. So for example a 15L arm would contribute 15 x 2= 30 degrees of timing when full against the stop.

    Total Advance: So far we have looked at initial advance and mechanical advance. Both of these combined gives total advance. Say for example initial was found to be 6 degrees, and we visually verified that the reluctor arm was on the 15L side. Total timing, theoretically, is then the initial + mechanical. In this case 6 + (15 x 2) = 36 degrees. If we shined a timing light on the marks (with vacuum hose disconnected and plugged), at idle we'd see 6 degrees, then as we increased the engine speed, we'd see more and more advance, until at some point the total centrifugal advance would be reached, and we would see 36 degrees. When exactly the total advance occurs is of great importance when it comes to performance, and we discuss this in the section below on "curving."

    Vacuum Advance: Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.

    Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.

    In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.

    Curving for Performance
    A timing curve is simply a plot of how much ignition advance takes place over the rpm range. In other words, when the timing advances is just as critical as how much it advances.

    When it comes to performance there are many different engine combinations, buildups, components, and uses….Each requiring slightly different timing curves. On the other hand if you have a stock motor, and do not care for every extra horsepower, you really do not need to do more than follow the shop manual procedures. However even a stock or mild daily driver motor can be made to accelerate faster with a five minute timing curve adjustment.

    The rule of thumb is that the higher the compression ratio, the less total timing it can handle before detonation, and also the higher octane rating it needs to control detonation. Low octane fuels ignite faster, thus require less timing advance. Conversely high octane fuel can handle slightly more advance. Dyno testing has shown that most small block Fords with 9:1 to 9.5:1 compression make peak HP with 38-42 degrees total advance. Engines with 9.5:1 - 10.5:1 run best with 35-38 degrees total, and above 11:1, should not go higher than 35 deg. total. When using power adders such as nitrous, super or turbo chargers, the timing should be advanced accordingly.


    The first step in curving a distributor is to set your initial and total advance. As detailed above and in the picture captions, the total is determined by the reluctor arm setting plus the initial advance. Ideally you should keep the initial between 10 and 20 degrees, and the total in the ranges listed above for your compression ratio. For example, if you are shooting for 40 degrees total, and your reluctor arm is on the 15L slot, you would have 30 degrees mechanical advance, requiring the initial to be set at 10 degrees.

    The second step is to dial-in how fast the distributor achieves the total advance. This is controlled by the springs which hold back the weights, under the breaker plate. A stock distributor usually has one light and one heavy spring, and brings the timing in really slow, such that the distributor may only reach the total timing at very high engine speeds, 4500+ for example. For performance driving, the best acceleration comes when total advance is achieved within the range of 2000rpm to 3000 rpm. To adjust this rate, you can replace the stock springs with lighter tension springs. You can also bend the tabs on which the springs connect to change their tension.


    Once you've set the initial and mechanical timing, and adjusted the curve, you should be very very close, if not right at, the optimum timing curve for wide-open throttle performance. You should use timing light at this point to confirm that the initial timing is where you set it, and steady, and then check the timing from idle to 3500 in 500rpm increments. The curve should increase a few degrees at every checkpoint until 2500-3000rpm, where it hits the maximum. After 3000 it should not go beyond the total advance.


    So How The Hell Do I Know How Much Advance I Need???

    Read On….

    Establishing Maximum Advance Requirement
    Notwithstanding the compression ratio and other factors, the characteristic that determines the maximum advance setting is the shape of the combustion chamber and the position of the spark plug.

    Combustion Chamber Shape and Spark Plug Location

    Combustion chambers and spark plug location and the number of plugs will have a marked effect on the time required to complete the combustion process. A large open chamber like a hemi which has a high surface to volume ratio, will combust more slowly than a wedge or modern pentroof chamber simply because it has more cold, metal molecules in contact with the combustion gasses which tends to slow reaction rates. For this reason, these chambers will require that the spark be initiated sooner to achieve PCP at the correct time.

    The slowest combusting chamber would be an open chamber with a large bore size and the spark plug at one edge of the chamber. The flame front has a long distance to cover to complete combustion. By placing the plug in the center of the chamber, you halve the distance that the front needs to travel and will be able to reduce the spark advance needed to achieve maximum power. Another solution would be to add another spark plug to create two flame fronts which would also require much less time to combust. This is the solution in most aircraft engines where big bores and poor fuel distribution and homogeny require solutions to increase ignition probability.

    Modern 4 valve engines with shallow pentroof chambers and a central plug location are fast, efficient combustors, requiring minimal advance for maximum power.


    Most small block fords use a heart shaped combustion chamber. These require 36-38 degrees. Factor in your compression ration from above and come up with a number in the middle. These few degrees difference can be made up for with a small adjustment to the initial timing to save from modifying the reluctor arms again.


    Establishing static advance requirement
    The static advance requirement for a modified engine is very much dependent on the duration of the cam fitted. Below is a table of advance requirements and expected idle speeds for a range of cam specifications. ON NO ACCOUNT use these settings before the maximum advance on the distributor has been correctly limited.

    Cam duration-----Idle speed expected------------------Advance
    ----270------------------600-800----------------------------10-12
    ----280------------------900-1000---------------------------12-14
    ----290------------------1000-1100-------------------------14-16
    ----300------------------1100-1200-------------------------16-18
    ----310+----------------1100-1400-------------------------18-20

    When establishing static advance the golden rule is never use less than 10; never use more than 20 degrees. The engine may well tolerate more than 20 degrees at idle, but the moment the throttle is opened and cylinder filling is improved it will ping heavily. One problem often encountered when using more static advance than standard is that the engine may 'kick-back' when starting causing the starter to slow dramatically, this can be confused with a flattened battery or worn starter motor. You may need to compromise by the odd degree or two if your engine will not tolerate the required degrees of advance at start-up.
    Static advance implies a measurement taken when the engine is stationery, however it is usually set at idle in order that any latency in the distributor drive gear is taken up. A rough setting can be made when the engine is still, but it MUST be set at 1300RPM or lower with the vacuum advance disconnected so that any latency is taken up and the centrifugal advance has not yet started its operation.

    Establishing mechanical advance requirement
    We have our desired static and maximum advance figures already calculated, so now we can use the same simple formula to establish how much centrifugal advance we need from the distributor.
    Example:
    Maximum advance 38 degrees, required static advance 18 degrees (38-18) = 20 degrees required.
    In our example the standard distributor is designed to give maximum advance from a starting point of say 10 degrees of static advance, if the maximum advance required is 38 degrees, then it's range is 28 degrees (38-10), this means that if the static setting is increased to 18 degrees, then the total advance will be 46 degrees (18+28), way too much. It is unlikely that the standard distributor will give the correct amount of advance, it will usually give too much. This is why we must restrict the total centrifugal advance that the distributor is capable of supplying to our new figure, in this case 20 degrees, then with the static setting of 18 degrees, the maximum advance will be 38 degrees (18+20), the correct figure.
    If the advance supplied is MORE than required, and this is highly likely, it means as expected that the distributor is supplying too much mechanical advance, and that the stops in the distributor must be bent to restrict the travel of the mechanism. If the advance supplied is LESS than required which is unusual, then the distributor is supplying too little mechanical advance and the stops must be filed to allow more travel of the advance mechanism.



    OK..So that is all great...But how do we make the adjustments they describe?????

    Lets have a look at it.....

    The Ford Duraspark distributor is an inexpensive and reliable alternative to the expensive aftermarket distributors. You can find them for about $52.00 US retail and the recurve spring kits are cheap at about $7.00 US. This recurving operation usually takes me about an hour or less. Just use care with the little parts as they like to migrate out of sight or flip half way across the room.


    Step 1
    Remove the two vacuum advance dashpot to main body screws and then the vacuum advance arm to breaker plate pin C clip


    Pull the advance dashpot away from the main body and pull the arm off of the breaker plate pin.



    Step 2
    Mark reluctor position as there are two slots.
    Remove reluctor from upper advance shaft. Use two pry bars or large screwdrivers and Do Not pry on the teeth but rather the beefy portion of the reluctor near the center shaft.





    Step 3
    Remove the two breaker plate to main body retaining screws. Rotate the pick up to gain access. lift off breaker plate.



    Step 4
    Decide which slot you want to use and if necessary remove the upper advance shaft retaining clip and springs so you can lift and rotate the shaft in to the proper position. If ordering a distributor from a parts store ask for one for a 1975 elite with a 460 4v engine. You will be more likely to get the lower number advance slot like a 10L or 13L rather than the 18 or 21L's. If you have a distributor with the larger numbered slots limit rotation via welding the slot smaller or placing a bushing around the pin to limit total shaft rotation.



    To figure approximate slot width for a given advance figure Multiply the number of desired centrifugal degrees by .013" then add .150" to account for the width of the stop pin.

    8L slot = 16 degrees centrifugal advance = .358”
    9L slot = 18 degrees centrifugal advance = .384”
    10L slot = 20 degrees centrifugal advance = .410”
    11L slot = 22 degrees centrifugal advance = .436”
    12L slot = 24 degrees centrifugal advance = .462”
    13L slot = 26 degrees centrifugal advance = .488”
    14L slot = 28 degrees centrifugal advance = .514”

    Step 6
    install the springs from the recurve kit and bend the tabs to keep tension on both springs so the advance shaft returns to its idle position



    Step 7
    Reassemble in the reverse order. Breaker plate, Reluctor, Vac advance dashpot and return the little clips to their proper place.



    Place the reluctor back on the shaft in its original position and align the roll pin slot in the reluctor with the roll pin slot on the upper distributor shaft. Carefully place the roll pin into place after fully seating reluctor on shaft and gently push it back into place with a hammer and a small punch. The 1/2 slots in both the reluctor and in the shaft together make a round hole for the roll pin.

    So what about Vacuum Advance?



    Vacuum Advance
    Under conditions of light or closed throttle, the volumetric efficiency of an engine is quite poor, and cylinder filling is affected to the extent that the effective compression ratio is much lower than the static or calculated compression ratio. In these circumstances the mixture will burn much more slowly than with a fully filled cylinder and the flame front will reach the piston quite late. This can dramatically cut the overall efficiency of the engine and its economy. Under these conditions the engine will tolerate and indeed benefit from advancing the timing by up to 15 degrees over its normal setting.
    The device that usually performs this trick is called the vacuum advance device. The way this works is to exploit the partial vacuum that is present in the inlet manifold when the throttle is closed or partly closed. A tube is connected from the manifold to a sealed diaphragm in the distributor, which in turn is connected to the distributors base plate. The suction deflects the diaphragm which turns the base plate against the direction of rotation of the distributor thereby advancing the timing, this gives much better throttle response on part throttle, and far better economy.
    Many people who tune engines disconnect the vacuum advance mechanism, and indeed on some distributors it is very hit and miss in operation and can cause anomalies in the timing. All in all however for a road engine, the vacuum advance retard should be retained if it is possible to do so (not always easy with sidedraught carbs). This will have a dramatic affect on economy and driveability especially on small throttle openings and when 'off-cam'.

    Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.

    Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.

    In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.

    Setting Vacuum Advance:



    Vacuum advance canisters are usually adjustable with a 3/32-in. allen wrench, as shown here. The small screw inside the housing adjusts the tension on the diaphragm spring. If you detect knocking and loss of power, back the screw out (counterclockwise) to decrease advance. If the engine pops and surges, tighten up the screw to increase advance.

    Note:When checking initial and total advance, always disconnect the vacuum advance hose. Otherwise you will get very high timing readings.

    Tuning Vacuum Advance
    The last step, after the total advance curve is set, is to dial in the vacuum advance if you have one. There should be a vacuum line connected from the carb, or the manifold, to the vacuum canister. There are two types of vacuum sources that you should be aware of. One type is known as "full" vacuum or "manifold" vacuum. This is a direct connection to the manifold, and if the hose is connected to this port you will get vacuum in the line at idle. The other port is a "timed" port, which only yields a vacuum above a certain rpm. At idle the line will have no vacuum. Most carburetors have both ports. On Holley's the timed is above the throttle blades, and the "full" is below, near the base. On Carter/Edelbrock carbs, the timed port is on the passenger side and the full is on the driver's side. The easiest way to confirm what port you have is to hook up a vacuum a gauge and check for vacuum at idle. The preferred vacuum source is the timed source. This way there is no effect on the initial timing setting.


    Remember vacuum advance is load dependent, so you cannot check it with a timing light with the car in neutral. The best way to set vacuum advance is by feel, under real driving conditions. Connect the vacuum line and drive the car up a steep, long grade, with the car in high gear and at a low speed, 30-40mph. Occasionally push the accelerator to the floor, and listen and feel for knocking and/or loss of power. If you detect this, immediately back of. This means the canister is advancing too much and you should adjust the canister so the diaphragm is 'tighter', by turning the screw counterclockwise.

    You can also adjust the vacuum canister clockwise until it does start to ping and then back it off 2 turns. This should set your Vacuum Advance perfectly.

    Well I hope this helped get all the info you need in one place!! I know I had a hell of a time to get everything together to accurately set my Ignition Timing.

    If you see anything that needs to be clarified or is misinformed...Please send me a PM and I will correct it.

    Cheers!!!

  2. #2

    Default

    This is a great candidate to archive!

  3. #3

    Default

    Thanks Foxchassis.
    I just got real tired of trying to figure out Duraspark Ignition Tuning from a bunch of difference sources. So I made my own Tech thread about it.

    Cheers

  4. #4

    Default

    I can PDF that if you want
    It puts the ATF in the T5... IT DOES AS IT'S TOLD!!!!!

  5. #5

    Default

    wow!! good job, excelent info !!
    86 SVO, jalapeno red, comp prep
    86 Gt t-top

  6. #6
    FEP Supporter


    Join Date
    Mar 2004
    Location
    North of Seattle, near the "Four-Eye-Field-of-Dreams"
    Posts
    2,063

    Default

    Bigbear, that was a very good write-up. There is a way to adjust the vacuum advance. This wil be a starting point, and may require a reader to borrow a vacuum pump. According to Ford " Technical Service Bulletin" number 111-A dated June 15, 1976, and pertaining to 1976 cars with 460 engines, it reads:
    "Install a Rotunda hand pump vacuum gauge ( part number 21-0014 ) or equivalent, to the distributor diaphram. ** Slowly apply vacuum to the diaphram until the gauge reaches 5" Hg. reading. ** With 5" Hg. vacuum applies to the distributor and engine speed at/or below 650 RPM, the total number of degrees advance on the crankshaft ( including inital ignition timing setting) should be 15 degrees. ** Adjust the vacuum advance screw with an 1/8th allen wrench 1-turn counterclockwise for each degree above specification, or 1-turn clockwise for each degree below specification " (end quote)

    The above setting of 15 degrees includes an initial timing of 6 degrees and equals a vacuum advance of 9 degrees at 5" Hg. of vacuum. This would represent a moderate load on the engine, not WOT. This setting is a good starting point for road tuning. Another good point or two for fuel economy is to allow the engine to operate at temps. of around 190 degrees and make sure that the temprature blend door on the intake snorkel is operating properly. Too much warm air into the carb will bring on detonation.
    One last thing.....make sure to have the "Felt Puck" inserted in the top of the dist. shaft and place 3 or 4 drops of 30 Wt. oil on it every 10,000 miles to keep the mechanical advance working freely.

    Old Neil..
    Check out the Northwest "4-Eye" BBQ here >>> WWW.NWFOUREYEBBQ.COM

    foureyebbq@hotmail.com (to be put on the BBQ list )

    Lots of pics of my ride for your viewing pleasure....
    http://www.cardomain.com/ride/2052657/1

  7. #7

    Default

    Good Info WHTLTHR79RS.

    I have one question though...How do you know..especially on Modified engines...that it is prododucing 5" Hg. vacuum at that RPM? I'm not saying you are wrong...I would just like to clarify.

    My understanding of it would be that vacuum would change depending on how far open the throttle plates are.

    Your description would be a great starting point as you suggest, however I think the best way to tune Vac advance for the wide varying combinations put together in the aftermarket would be road tuning.

    Possibly set the advance where you suggested and then road tune it as per the description in my post? I believe you want it to advance until it pings and then turn it back until it stops.

    Also...It has been suggested to me that in order to have an "Ultimate" Tuning guide I should address locking out the timing. I will put something together today for that and edit my post above.

    Cheers!!

  8. #8
    FEP Supporter


    Join Date
    Mar 2004
    Location
    North of Seattle, near the "Four-Eye-Field-of-Dreams"
    Posts
    2,063

    Default

    Bigbear, let's look at this again....

    I have one question though...How do you know..especially on Modified engines...that it is prododucing 5" Hg. vacuum at that RPM? I'm not saying you are wrong...I would just like to clarify.

    My understanding of it would be that vacuum would change depending on how far open the throttle plates are.


    The engine is not the unit that is producing the 5 inches of vacuum, it is the hand-held vacuum pump, and you have hooked up the vacuum pump to the diaphram with a short vacuum hose, and pulled the plunger on the pump to reach 5 inches....like a bicycle pump in reverse, but the hand held pump will HOLD what ever vacuum you apply. It is very accurate. The reason that the "TSB " states to run the engine @ 650 RPM is to make sure that the mechanical advance weights will not start to do their thing, and the only two factors will be the initial timing and the small amount of advance produced by the vacuum diaphram. Depending on how wild your engine is built, and what it's idle speed is, will dictate at what RPM you would want the mechanical advance to kick in. I personally like to see the mechanical advance start at about 1400 RPM.
    You are correct that the vacuum will change depending on how far the throttle plates are open, but engine RPM also plays a role too...Want real fun ?? buy a 3 inch round hand-held vacuum gauge and "Tee" it into the vacuum hose that is hooked up to the diaphram, place the vacuum gauge on your dashboard near your tachometer, and go drive around at different engine speeds and loads. Start out @ 1500 RPM with 1/3rd throttle in 2nds gear and hold your foot VERY steady while the engine runs up to 3500 RPM and watch what happens to the vacuum reading. With this setup, you will know exactly at what RPM and vacuum reading your pinging will occure, then you can duplicate the result in the shop. That is how a dyno works to fine tune timing VS. load. And it is possiable to have more vacuum advance that you need and still not ping due to a good head design or cam timing...sometimes less is more. By the way, I have run a 3 inch vacuum gauge in my 78 Ford pick-up with a 460 for the last ten years and would not be with out it....not with todays fuel prices....that's why I tell people to " have fun and keep an egg under your foot"....you will soon discover that the further down the scale that vacuum gauge drops, the greater the smile on your face when the tires go up in smoke... I call it the " Giggle Gauge" and it can range from a smile to hysteria.....just ask Schoolboy.
    One last thing....when the sparkplug fires, the fuel and air ignite and produce incresed heat and pressure on the piston. The flame front starts at the plug and TRAVELS across the top of the piston smoothly, it is not an explosion, it is a controlled burn. when this event is happening, the pressure on the other side of the piston is growing rapidly and if the plug fires too soon, the pressure on the other side of the piston will increase too fast and start it's own burn which runs across the top of the piston back toward the plug. when the two flame fronts meet, that's what you hear as "PING", and you have lost any power you were trying to achieve...I hope this helps...and you are on the right track.

    Neil
    Check out the Northwest "4-Eye" BBQ here >>> WWW.NWFOUREYEBBQ.COM

    foureyebbq@hotmail.com (to be put on the BBQ list )

    Lots of pics of my ride for your viewing pleasure....
    http://www.cardomain.com/ride/2052657/1

  9. #9

    Default

    I see a couple of things I would like to point out...

    The reason that the "TSB " states to run the engine @ 650 RPM is to make sure that the mechanical advance weights will not start to do their thing, and the only two factors will be the initial timing and the small amount of advance produced by the vacuum diaphram. Depending on how wild your engine is built, and what it's idle speed is, will dictate at what RPM you would want the mechanical advance to kick in. I personally like to see the mechanical advance start at about 1400 RPM.
    Most modified engines won't idle at 650RPM. Mechanical Advance won't start coming into effect until at least 1000RPM's but more than likely around 1300rpm. I know my setup wouldn't even entertain the idea of idling at anything under 800rpm and that would be a challenge..My car idles best at around 1100 and there is no mechanicl advance being applied at that time. My mechanical advance starts to pull at around 1350rpm.

    buy a 3 inch round hand-held vacuum gauge and "Tee" it into the vacuum hose that is hooked up to the diaphram, place the vacuum gauge on your dashboard near your tachometer, and go drive around at different engine speeds and loads. Start out @ 1500 RPM with 1/3rd throttle in 2nds gear and hold your foot VERY steady while the engine runs up to 3500 RPM and watch what happens to the vacuum reading. With this setup, you will know exactly at what RPM and vacuum reading your pinging will occure, then you can duplicate the result in the shop
    This is exactly what I was trying to get you to say...A vacuum pump will not be of any help without knowing what kind of vacuum your particular engine makes and at what RPM.

    Also ..You need to put the car in high gear and run it up an incline to produce load on the engine. A vacuum reading on a flat surface where the engine is not being loaded won't help you set your vacuum advance.

    The flame front starts at the plug and TRAVELS across the top of the piston smoothly, it is not an explosion, it is a controlled burn.
    This is correct however I felt it was beyond the scope of the article.

    when this event is happening, the pressure on the other side of the piston is growing rapidly and if the plug fires too soon, the pressure on the other side of the piston will increase too fast and start it's own burn which runs across the top of the piston back toward the plug. when the two flame fronts meet, that's what you hear as "PING", and you have lost any power you were trying to achieve
    This is partially correct. Timing to far advanced or retarded will have different effects.


    Timing is about finding the correct "Time" to fire the spark plug. It has to do with how fast the mixture in the chamber will burn, what pattern it burns (spark plug placement and combustion chamber shape and size), quench, squish and many other variables..which again I felt were beyond the scope of this article.

    Regardless of which way you do it..you still have to take it back out and road tune it because you won't be able to make it ping idling in the garage.

    That is whay I would reccomend taking the allen key with you and just adjust the vac can until it pings..then back it off a turn at a time until it doesn't ping anymore.

    I think you know what you are saying but maybe not elaborating on it enough..

    Thanks for the posts!!

    Cheers

  10. #10
    FEP Supporter


    Join Date
    Mar 2004
    Location
    North of Seattle, near the "Four-Eye-Field-of-Dreams"
    Posts
    2,063

    Default

    Bigbear, I wish you lived close to me, I would give you a hands on tuning session, and I would also supply the beer...
    I can only type so much until my fingers and hands start to hurt, hey man, I am in my 50's....
    The point about the engine idling @ 650 is to make sure the mechanical advance system was not operating. If your engine idles at 1100 and you know for a fact that your mechanical timing starts at 1350 then you are fine. This quoted information was for a stock 460 of 1976 vintage, but the principles is what Iam trying to teach. You and I both like to have the mechanical advance start at about the same RPM.

    Setting the vacuum diaphram with a hand-held vacuum pump is nothing more than a starting point to do the road work with. You have NO gaurentee that a new vacuum advance diaphram that comes out of the box is adjusted to have ANY movment at all until you test it

    Start out @ 1500 RPM with 1/3rd throttle in 2nds gear and hold your foot VERY steady while the engine runs up to 3500 RPM and watch what happens to the vacuum reading. With this setup, you will know exactly at what RPM and vacuum reading your pinging will occure, then you can duplicate the result in the shop

    I was trying to explain two things here: first, if you do what I asked in the first part of the above, you will see the vacuum gauge read a "low" amount ( I won't give any numbers here because any number will vary from engine to engine, but the results will always be the same) and as the engine speed increases ( with the exact same throttle opening as you started with ) the vacuum gauge will produce a higher reading up to a point of a plateau, which will be less than you would see if you took your foot off the throttle and coasted ( in gear, of course ). Here is the second part: Let's say you were in high gear, at 2800 RPM, going up a medium hill, and your dash mounted 3 inch vacuum gauge was reading 8 inches of vacuum. you hold this load for a while cause it;s a long hill. you are not working the engine too hard, but after 5 seconds or so, you start to hear some detonation. You now know these facts: A- your engine was turning 2800 RPM...B- your vacuum gauge read 8 inches vacuum...C- detonation occured. If at this point, you applied a little throttle, and brought the vacuum gauge reading down to 5 inches and the detonation stopped, you have too much vacuum advance. Now what do you do ?? You should start keeping records of your findings. AND you can go back to your shop, hook up your timing light, run the engine at 2800 RPM with the vacuum hose to the vacuum diaphram disconnected, and read the total timing you have at that point, the total of both initial and mechanical, and write it down. Now return the engine to idle, take your hand-held vacuum pump and pull 8 inches of vacuum and record how much vacuum advance you have. At this point, you have a base line to go by for future testing. Make you adjustment to the diaphram, pull 8 inches vacuum again and record the amount of the new vacuum advance timing. Go back to the same stretch of road, and exactly repeat the load and speed of the engine. Problem not fixed yet? Now you can start to road tune the vacuum advance diaphram. when the ping stops, go back to the shop and record the numbers again with the new settings. You may ask " why the hell do all of that ? " good point: because when the refineries change the blend of the fuel to compensate for the changing weather and seasons and you car starts to ping again or the performance and milage go in the toilet, you have records to refer to rather than memory.

    Quote:
    when this event is happening, the pressure on the other side of the piston is growing rapidly and if the plug fires too soon, the pressure on the other side of the piston will increase too fast and start it's own burn which runs across the top of the piston back toward the plug. when the two flame fronts meet, that's what you hear as "PING", and you have lost any power you were trying to achieve


    This is partially correct.

    Sorry, but I believe this to be totally correct in it's context. any time a given amount of air is compressed, the air is heated. When a flame front ( from a spark plug) starts to travel across a piston, regardless of head shape, squish area or any other secondary factors, the air (and in the case of an internal combustion HEAT engine, which we all drive) and fuel mixture on the side of the piston that is opposite from the spark plug is heated because it is being compressed by the flame front of combustion. If the heated and highly compressed fuel/air mixture reach a point of excess, the mixture will self ignite, causing a reverse flame front to crash into the ignition caused flame front...you got "ping".

    Timing to far advanced or retarded will have different effects.
    Very true, but just to keep the record straight, retarded timing will never cause detonation.

    Timing is about finding the correct "Time" to fire the spark plug. It has to do with how fast the mixture in the chamber will burn, what pattern it burns (spark plug placement and combustion chamber shape and size), quench, squish and many other variables..which again I felt were beyond the scope of this article.

    Finding the correct "time" to fire the plug is the ONLY thing timing is about. The rate that the mixture burns is controlled by Octane, and the shape of the chamber and the other factors try to control the pathway of the flame front to deliver the most effecient load to the top of the piston. And yes this is beyond the scope of the article, but you gotta agree that the readers are learning something.

    I think you know what you are saying but maybe not elaborating on it enough

    I do know what I am saying, I just want anyone reading this to understand that in anything mechanical there will be variables, and my first post was a guide to get started on setting a vacuum advance diaphram before the road tuning took place.

    Five days a week for 10 years, I tackled (and solved) drivability problems including detonation and poor fuel economy while maintaining emission standards and keeping the customer happy. I averaged 11 to 15 cars per day and maintained a 98 % satisfaction record with my customers. I also built some nasty performance motors including a 67 mustang 427 that ran 3 hundredths of a second off the national record. Tuning was my speciality, but spelling and grammer was not.

    Like I said earlier, wish you lived closer to me, so we could bench race over beer once in a while....by the way....what IS your name and background, .....you have gotten more print out of me that most people have......

    Neil
    Check out the Northwest "4-Eye" BBQ here >>> WWW.NWFOUREYEBBQ.COM

    foureyebbq@hotmail.com (to be put on the BBQ list )

    Lots of pics of my ride for your viewing pleasure....
    http://www.cardomain.com/ride/2052657/1

  11. #11

    Default

    Hey Neil,
    My name is Barry and I have been heavily into modifying and racing cars since I was 16. I am 30 now. I attended community college and took my Automotive mechanical repair course. Graduated 1st in my class. I started my apprentice training to become a certified and licensed mechanic in my provice but found that I didn't enjoy ball joint, tie rod end, wheel bearing, exhaust replacement, fuel injection diagnosis as much as I like tackling modifications and building power. I am still very much into performance vehicles and building power.

    You sound like a guy I would really like to bench race with and have a beer or two. (Maybe even some track time..without the beer of course)

    Anyway..I totally agree with your methods and therory(proven) you are suggesting in this thread. I was just trying to get you to elorborate on your principals for the readers of this thread.

    Let's say you were in high gear, at 2800 RPM, going up a medium hill, and your dash mounted 3 inch vacuum gauge was reading 8 inches of vacuum. you hold this load for a while cause it;s a long hill. you are not working the engine too hard, but after 5 seconds or so, you start to hear some detonation. You now know these facts: A- your engine was turning 2800 RPM...B- your vacuum gauge read 8 inches vacuum...C- detonation occured. If at this point, you applied a little throttle, and brought the vacuum gauge reading down to 5 inches and the detonation stopped, you have too much vacuum advance. Now what do you do ?? You should start keeping records of your findings. AND you can go back to your shop, hook up your timing light, run the engine at 2800 RPM with the vacuum hose to the vacuum diaphram disconnected, and read the total timing you have at that point, the total of both initial and mechanical, and write it down. Now return the engine to idle, take your hand-held vacuum pump and pull 8 inches of vacuum and record how much vacuum advance you have. At this point, you have a base line to go by for future testing. Make you adjustment to the diaphram, pull 8 inches vacuum again and record the amount of the new vacuum advance timing. Go back to the same stretch of road, and exactly repeat the load and speed of the engine.
    This is exactly correct. I was just trying to draw the information I knew you had out of you...

    Sorry, but I believe this to be totally correct in it's context. any time a given amount of air is compressed, the air is heated. When a flame front ( from a spark plug) starts to travel across a piston, regardless of head shape, squish area or any other secondary factors, the air (and in the case of an internal combustion HEAT engine, which we all drive) and fuel mixture on the side of the piston that is opposite from the spark plug is heated because it is being compressed by the flame front of combustion. If the heated and highly compressed fuel/air mixture reach a point of excess, the mixture will self ignite, causing a reverse flame front to crash into the ignition caused flame front...you got "ping".
    This is correct...That is why you have to have your timing advanced just enough to begin the burn so it burns across the piston before this occurs, and creates the downward pressure on the piston.

    There are so many varibles, like you said, Involved in Engines and especially performace engines..I think that is what drives me to learn and try new things.

    I totally agree that the readers are learning something and I must admit I have completely enjoyed this discussion with you.

    Cheers

  12. #12
    FEP Supporter


    Join Date
    Mar 2004
    Location
    North of Seattle, near the "Four-Eye-Field-of-Dreams"
    Posts
    2,063

    Default

    Thanks for the kind words Barry, now I have a little experiament for you to try in your spare time......Hook up a vacuum gauge to your motor so you are reading manifold vacuum ( full vacuum at idle, ect.) and remove the vacuum hose to the advance diaphram. Set your idle speed just a little lower than normal by about 100 rpm, if the motor will stay reliable, and without the timing light hooked up, advance the timing while watching the vacuum gauge. when you get to a point of the highest vacuum reading, stop advancing the timing and start to retard the timing until you see a reduction of 2 inches of vacuum from your highest point. Lock down the dist. and hook up your timing light and see how close you are to your preferred initial timing setting. Let me know the results. This is how the mechanics did it in the 50's for a quick setting....

    Neil
    Check out the Northwest "4-Eye" BBQ here >>> WWW.NWFOUREYEBBQ.COM

    foureyebbq@hotmail.com (to be put on the BBQ list )

    Lots of pics of my ride for your viewing pleasure....
    http://www.cardomain.com/ride/2052657/1

  13. #13
    FEP Senior Member AaronATX's Avatar
    Join Date
    Aug 2004
    Location
    Southsiiiiide ATX
    Posts
    769

    Default

    I've never owned a carb'd car, all my mustangs have been EFI, but there is still tons of great info here. Thanks guys.
    No more 4eyes

    Some crappy 90 HCI coupe for now.

  14. #14

    Default

    Your welcome Arron.

    Sounds good Neil. I am actually going down to work on the car this weekend. I will try that.

    I hope I can bounce ideas off you every once and a while..Sometimes it helps to get experianced second opinions..and work through problems with someone..

    Cheers

  15. #15

    Default

    WOW! Talk about learning something new every day! Thanks for all the information everyone. I enjoyed reading this thread. Great information for us carb'd guys running duraspark stuff.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •