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Century Performance Center, Inc. » Ignition and Timing Settings
| Ignition and Timing Settings |
 Your Engine's Ignition System and Timing Settings
Ignition Timing can be a tricky experience and there are some things you need to know about your engine and how ignition timing actually works. Hopefully this section will give you some insight into timing curves, changing mechanical and vacuum advance settings and more.
What is the Ignition System?
Your ignition system is the part of your vehicle/engine that fires, or ignites, the compressed fuel and air mixture within your engine. The system combines a primary voltage delivery to the ignition coil and electronic control units and secondary voltage released from the coil travels through the distributor, out through the plug wires, to the spark plugs where it jumps the gap and ignites the mixture.
| Yes, I know there are Magneto Systems that do not rely on primary voltage as well as D.I.S. Ignitions (Distributorless Ignition System) that do not have a distributor, just an assortment of computer-controlled coil packs. For the sake of the fact that MOST of the ignitions in service and in our racing and performance vehicles today are not the latter descriptions, I have not taken excessive time or detail to describe them in this article. |
Your ignition system consists of supply voltage (in most cases a 12-volt battery), an on/off switch (your ignition switch), a spinning portion of your distributor (or crank trigger) that houses a triggering device, an ignition coil to deliver 20,000-50,000 volts of secondary voltage, spark plugs, and spark plug wires to get the current to the plugs.
How the Ignition System Works?
Your electrical system (typically a 12-Volt battery) gives supply voltage to your coil and ignition unit (if electronic). When the coil is told by the trigger in the distributor (contact points, electronic module, magnetic breakerless, Mallory Unilite®, Crank Trigger, or other type of trigger) to release voltage, the coil builds secondary voltage and releases it to travel through the coil output wire. It does this at a very high rate of recovery speed.
The spark then travels into the distributor cap into the spinning rotor and out the corresponding terminal in the distributor cap that the rotor is aimed at and then through the spark plug wire to the spark plug. It is now the gap in the spark plug that creates the actual spark in the combustion chamber when the secondary electrical voltage now must jump the spark plug gap to "ground". It is the "jump" that is the spark that ignites the compressed air/fuel mixture.
That's the easy part!
The trick to the ignition system is in when the spark actually occurs at the spark plug. This is the ignition TIMING. Timing is controlled by the relationship of the position of the piston to when the spark occurs. If the ignition spark occurs too soon it can actually push against a piston traveling up the cylinder as it is compressing the fuel/air mixture. This causes detonation, lost power, much higher combustion temperatures, backfires out the carburetor, and early internal engine part failures. If the spark occurs too late, the ignition of your fuel mixture occurs after the piston is traveling back down the cylinder. This is wasted energy, unburned fuel, high emissions, and lost power.
How do you control the timing you ask? Well, late model cars use computers that monitor engine load, piston position, incoming air quality and temperature, engine RPM, and more. The computer then tells the ignition system what the engine needs based upon those inputs from the sensors and a pre-determined MAP within the computers' programming. On older OEM engines, and most race cars with aftermarket distributors, the ignition system used a simple mechanical advance (or a combination of mechanical and vacuum advance) system built into the distributor. You would set "initial" idle timing with a timing light looking at the balancer mark and timing tab indicator. As RPM increases, the mechanical advance (weights and springs) moves due to the inertia occurring within the distributor, thereby changing the timing causing the point that the spark plug receives voltage to also change in relation to piston location. You can tune your timing curve (shown later on this page) for your engine's optimum performance curve by changing initial, mechanical as well as vacuum advance settings and parameters.
What this means is that if you have your initial timing setting at 10° advanced, your ignition is firing that cylinder at ten degrees "before" top dead center (BTDC). TDC is where the piston is at it's highest point in the cylinder. As engine RPM increases there is less time to be able to fire the cylinder. The parts are moving faster so you must get the spark in there sooner, but not too soon that it will cause detonation or engine damage.
Say for example that you have that 10° initial timing and then you have mechanical advance of 24°. This means you have a "Total" timing of 34°.
10 + 24 = 34
Now, that 34° does not happen all at once ... the "Timing Curve" is the staging of advances, or increases, in your timing. Remember, as the RPM increases it puts inertia against the weights and springs that move in the distributor causing this added timing. All of these values are adjustable by changing initial settings, the weights that control the MAX advance, as well as the spring pressures that control the RATE (or speed) of advance..
Now, when adding vacuum advance to the equation you would have the total (34 degrees) PLUS the additional vacuum advance. On a street application, adding 8-10 degrees is plenty. But, each individual application will vary slightly.
What Tools Do I Need to be Able To Work On My Ignition System?
The tools you need to work on your ignition system are not too complicated. Read the listing and the descriptions below.
Basic Hand Tools: This includes screwdrivers, box end wrenches, socket set (usually 3/8" drive) and possibly in metric for newer applications, and in standard for older vehicles.
 Timing Light: Snap-On® Computerized Tach/Advance Timing Light #MT2261OK (shown at right) before you freak out I'll tell you up front ... "You need tools that are correct for the time and technology available". What this means is that you need an ADVANCE TIMING LIGHT. This is a timing light that is adjustable so that you do not have to shoot the high numbers on your timing tab (over zero) or fully degree your balancer to be accurate, as well as view, high RPM timing readings. You adjust the timing light to always read "Zero" on the balancer/timing tab. You will adjust the light to read zero at a given RPM and then read "the light" to give you the actual timing. If this is confusing, oh well, buy one and read the directions! Expect to ante up a BIG dent in the checking account for an accurate and reliable advance timing light ... the computerized Snap-On® advance timing light (at right) is the one I use and it costs over $450.00. You can also order a generic low-priced advance timing light from Harbor Freight Tools for about $50.00 which will be fine for the average do-it-yourselfer.
 NOTE: I recommend the Snap-On® because it has lasted the longest. I've over the years owned the Craftsman, Harbor Freight, and MAC tool versions and have seen all fail. In fact I had 2 or 3 of the MAC units fail, they sucked with Multiple Spark Ignitions (Mallory Hyfire®, MSD®, etc), and their warranty was horrible. I still have a near-new dead MAC® light in one of the cabinets in the shop. The Snap-On® has never let me down, and I've had it for about a decade. I'm not getting paid or reimbursed to recommend the Snap-On®.
 Digital Multi-Meter/Ohm Meter: Yes, this can be "expensive item #2" if you want the quality of a Fluke (brand name) Digital Multi-Meter (DMM). I will not bother to scare you with the pricing, only to say you will be up near 4-digits! If you work on late model vehicles, this tool is more useful and used more often than a screwdriver. You use the DMM to measure voltages at all sources on a vehicle, measure resistance, electronic pulse widths, troubleshoot power spikes, and more. This tool is definitely a required friend if you want to take the time to learn and use it's features and time saving benefits it gives you.
Tests include: Plug wire resistance with the Ohm Meter, primary and secondary coil tests, voltage spikes, Battery voltage, charging voltage, amperage draw, dwell (if you use contact points ... hehehe, excuse me as I laugh at Model "A" technology), temperature readings, electrical shorts, battery drains, and even more tests if your vehicle is computer-controlled.
Vacuum Gauge: I will not describe it's benefits here, but it is a mandatory tool for anyone's tool box. More info on Vacuum Gauge Tuning is HERE.
Specialty Tools: Specialty tools are any tool that is optimized for working on a vehicle's ignition system. Specialty tools are any tool that is optimized for working on a vehicle's ignition system. Specialty tools are any tool that is optimized for working on a vehicle's ignition system. Specialty tools are any tool that is optimized for working on a vehicle's ignition system.
These include:
- Specialty wrenches designed for distributor hold down bolt tightening and removal.
- Plug wire "puller pliers" to prevent boot damage when removing the plug wires from the spark plugs.
- Spark Plug "Starters" that are basically a piece of flexible rubber tubing the goes over top of plug to ease plug installation into the cylinder head.
- Spark Plug Gapping Tool ... you get what you pay for and the feeler wire (or gauge) method is not the accurate or fast way.
- Spark Plug Wire assembly tools (stripper, crimper, etc).
Other Possible Tool Requirements Include:
- Tools for finding TDC (Top Dead Center), usually part of a camshaft degree kit.
- 4 or 5-Gas Analyzer. Yes, this is a smog machine ... most of you will not be able to get one or afford it, though this machine is a definite helper for finding optimum timing settings based upon exhaust gas emissions. I will not describe the procedure here, but it works! If you have a friend that has a shop and he or she offers you access to it, it can be an invaluable tuning device.
- Shop manuals as well as ignition product documentation. This is good for stock as well as performance ignition product applications.
What is Initial Timing and Total Timing?
Initial timing is that setting you make while your engine is idling with a timing light. This is typically between 4° ATDC (After Top Dead Center) to 16° BTDC (Before Top Dead Center). For performance applications "in most cases" you want as much initial timing as the starter can handle (the more timing the more cylinder pressure that the starter must overcome to crank the engine). Too much initial timing, besides the starter load, can also run the HC (Hydrocarbon) emission levels beyond legal or breathable levels <hint to the smog machine as a tuning tool above>.
Total timing is the calculation of the combined initial and mechanical advance timing settings (max). This "can" also include your vacuum advance though, I like to describe it as "total timing plus vacuum advance". Since vacuum advance is a nearly inconsistent value I like to use it after I have set up the correct mechanical values in the distributor. At times I must use the vacuum advance to generate the timing values I require, but I try to only use it as an "economy" tool to give a street driven vehicle more efficiency and throttle response by this addition.
What is a Timing Curve?
The timing curve is the mechanical timing values plotted over an RPM curve. What this means is that at a given RPM based upon the weights and springs used in the distributor you will have a specified amount of timing advance. Remember, as your engine RPM increases, so does the inertia against the distributor weights within the distributor. The springs holding the weights is the opposite resistance force that controls the speed, or rate, that the weights move "out" causing the distributor advance plate to move which advances the timing. So, what happens is that at each RPM change there is a variance in the amount of timing advance up to a point in which the weights usually hit a "stop" that does not allow them to move out (advance the distributor) beyond that point.
Changing the springs to a lighter one (or both) will make the advance occur faster, and of course running a heavier (stronger) spring will slow the advance rate. You can also in most cases modify the weights (or stops) as to what the advance limit will be. Mixing springs to control the desired advance rate is how you modify your timing curve.
How Do I Change the Mechanical and Vacuum Advance Settings?
Mechanical advance (also called centrifugal advance) as stated above, is adjusted by change the springs that control the weights and in many distributors you can also adjust or modify the advance "stop point". The stop point is where the mechanical advance no longer continues. On a Mallory distributor there is a wrench you use to adjust the stop point (in degrees). On other OEM and aftermarket distributors you need to change the weights by going to a different weight or modifying the weights to control the stop position.
This is a job that can be done by just about anyone, but it takes the correct tools and some trial and error. In most all cases, aftermarket distributors are good for your engine right out of the box, but when change needs to be made you will need assorted springs, a distributor machine, fully degreed balancer, or an advance style timing light.
You start the engine and write down each timing number at 100, or 500 RPM intervals. This means you write down the timing at idle, then raise the engine speed in 100 or 500 RPM increments (whatever you decide), and write down each one of the timing readings. To make the rate faster (more timing advance sooner), you install lighter combination of springs. To make the rate slower (less timing advance), you install a combination of stiffer springs.  NOTE: Too much timing too soon can cause detonation problems, having the timing come on too slow can adversely affect performance and efficiency.
With adjusting the vacuum advance it is on the same principle, except you are now adjusting the pressure on the diaphragm in the vacuum advance can. NOTE: Only those vacuum cans with the octagon body near the nipple can be adjusted. If you are working with an OEM style distributor you must either change to an adjustable can or change cans to one with a different rating. (Most ALL aftermarket vacuum advance distributors are adjustable) On the adjustable vacuum advance cans you simply insert a 3/32" Allen Wrench in through the vacuum line nipple on the can. Turning the Allen Wrench one way or the other will add or subtract the preload pressure on the vacuum diaphragm. Lower pressure offers more vacuum advance, higher pressure lowers the amount of added vacuum.
It is our recommendation that when you are using vacuum advance distributors, that you connect the vacuum advance to "full manifold vacuum". There are two schools on where to connect the vacuum advance line. On older applications the connection point was to "ported" vacuum. Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases. This was fine on older applications with high lead fuel and other ancient engine designs. Using this set up today can cause detonation problems, overheating, and other grief.
With our suggestion of using the vacuum connection to full manifold vacuum, the port will be drawing vacuum below the throttle blades. A good running street engine will have a measured vacuum at idle between 14"-20" of manifold vacuum. Now, this will give you a ton of advance at idle, but as load increases (vacuum drops) you will take timing away. This is excellent for the faster burning fuels offered today as well as in the fact that when you put your foot into the throttle and get the RPM building, you DO NOT need or want additional timing. On a RV or tow vehicle, when you put your foot into the throttle and downshift to climb a grade, you DO NOT want added timing that will slow the vehicle and add heat. You want the added timing for subtle throttle response, and low load engine efficiency. So, when you are cruising at freeway speeds or in town traffic, you have the added timing to save fuel, add throttle response, and overall give you a better feel.
What Modifications Can Be Done to Improve My Ignition System?
One of the common early modifications to increase the performance or your vehicle is to upgrade the ignition system.
 Here's The Secrets That Most Ignition Manufacturers and Speed Shops DO NOT Tell You:
UNLESS your vehicle is also getting performance improvements that increase either the amount of fuel your engine will be using (camshafts, cylinder heads or porting, superchargers, turbochargers, nitrous, and other modifications along these lines) or the demand for higher RPM, You SHOULD NOT get a substantial performance or horsepower improvement from an aftermarket ignition. On a stock engine you should really not see an improvement.
NOTE: Of course, if you are using a prehistoric contact point (yes, dual points too) ignition system or have an engine tune-up that is not where it should be (too much fuel from poor jetting or a bad carburetor, too much plug gap, worn ignition components or just an engine that is getting tired), you will see an increase in performance because of basically a "Band-Aid" with the better ignition components to hide obvious other problems.
Now, if you do not fall into the categories above because some idiot behind a counter (or on the phone at the "sell a gazillion mail-order parts" outlets) tried to sell you something you did not need, let's get into really upgrading your ignition.
Of course, there are a few myths of what your ignition system can do. We all see the advertised "Power Output Levels" that many ignition manufacturers use to build interest in their products. Do you feel the fish hook locking through your lip with the words "sucker" on your forehead? Yes, it's true ... many ignition manufacturers will tell you whatever it takes for them to get you to believe that their ignition is the best. One of the good ones (snake oil advertising) is advertised coil output and also aftermarket Ignition Unit output (usually an Inductive Electronic or CD "Capacitive Discharge" Unit). What people tell you is that you MUST have the highest output ignition unit because it's the best. Do you actually believe this? If so, read the Italic text above in this paragraph.
What really happens is that your engine (each cylinder) will ONLY use the amount of voltage it takes to jump the spark plug gap and fire the air/fuel mixture in that cylinder. Guess what I'm going to tell you now? If you guessed that I will tell you, "Your engine requires a lot less spark than what is advertised", then you are right. Yes, it's true ... even if you have a Gazillion Millijoules of advertised output, if your engine only needs 20,000 volts to jump the plug gap, that's all the unit will give. What they should tell you is that the unit "can" deliver up to that rating if the engine demands it. So, does your engine really demand that much voltage output ... probably not.
Want another misnomer? Well, this one is on multi-strike ignition systems. Well, you probably may not have guessed it, but the analog multi-strike has less time as engine RPM increases to get off as many sparks. Do these extra sparks help your engine? Not consistently on every application, the major concern is the actual spark duration in "Crank Degrees" that you have for each spark on each cycle. Most aftermarket ignition manufacturers give you 20° of spark duration with each spark. Now, this spark will not carry full voltage over the entire 20° . As the spark duration continues it loses voltage output. The reason behind the longer spark is to make sure there is a complete and thorough burn of the air fuel mixture. With high dome pistons, tight valve shrouding and other issues, you can get portions of your mixture that do not get a decent ignition. By holding the spark up to 20° of crankshaft duration you virtually eliminate these problems (if your engine is in proper tune). Having a greater voltage hold over the entire 20° should be more of a concern to you than peak voltage output. The newer digital multi-strike units have improved in efficiency and power output and we are seeing greater gains in actual "benefits" due to modern circuitry, but again it gets down to that important 20°.
OK, now the parts:
Ignition Coils, Electronic or Magnetic Trigger Distributors, Performance Wire Sets, Inductive Electronic or Capacitive Discharge (CD) Ignition Units, Electronic Timing Controls and Retards are the most common ignition upgrades.
 The ignition coil is the workhorse of the ignition system and must be the first upgrade you consider. OEM or coils not designed for your application can overheat, cause mis-fires, boil over (possibility of causing a vehicle fire) and otherwise just cause you grief. You must have a coil designed for electronic ignition if that is what you are using. Also, there are a few coils on the market that are for "Limited Use Racing" as in Drag Racing or short term use. These coils are designed to give Maximum Output, but cannot safely do it for extended periods. You should not use coils with this designation on the street or in circle track applications. I like to use the analogy that a coil choice is like your shoe selection. You would not purchase Sorel winter boots to cross the Mojave Desert in July, nor would you wear rubber sandals to climb Mt Everest. Pick your coil to meet the demands of your application and it's intended use.
Electronic or Magnetic Trigger distributors are "only" your triggering device. A performance distributor gives you better control of timing curves and triggering accuracy. In some of the later model computer-controlled engines, a performance distributor is not available as well as not required. Technology has increased to a point that on many late model applications your distributor is perfect the way it is. If you have a computer-controlled distributor there is NO mechanical advance in it. These distributors will only work on computer-controlled applications. In these later computer-controlled applications, the distributor is more or less just a convenient place to hang your plug wires.
 Performance Wire Sets are still argued about and hopefully I can clear this mess up. One of the biggest arguments is on solid core wires vs. spiral core (or suppression) wire sets. If you have anything that is electronic on your vehicle (computer, ignition unit, triggering module, radios, etc) You MUST Use spiral core wire sets. There is not much gain going to solid core wires unless you are using a Magneto, and many racers are still using a spiral core wire with their magnetos because of the computerized vehicle controls and monitors that are in use. With the low resistance of the spiral core wires it is ridiculous to take a chance using a solid core wire and damaging another component on your vehicle.
How do you damage electronic parts with just a set of plug wires you ask? I knew you would ask. Well, have you ever heard of EMI (Electro Magnetic Interference) or RFI (Radio Frequency Interference)? Either or both of these are generated by your ignition system and when running a solid core wire it is like leaving your front door of your house open with a neon sign saying "Rob and Rape Me, Come on In!" You are leaving your electronic parts on your car wide open for damage from EMI and RFI that is released from the wires at each spark cycle. More info is in the Spark Plug article.
I cannot leave this out ...
Spark Plug Wire Shielding Thickness:
Here is another advertiser-abused method to confuse and milk more money from the consumer. When you are reading about plug wire size (5mm, 7mm, 8mm, 9mm, 10mm, 10.5mm, etc) you are only being told about the thickness of the cover, or shielding around the core of the wire, not necessarily the quality of the wire.
If you look at the image at right you will see a simple comparison of wire thickness. This is not a dead accurate image, but it gives you an idea. The center cores are all equal, and we've made minor changes to the thickness of red-colored shielding ring. If you actually take a micrometer or digital caliper and see how thick 1mm really is you will see how you've been duped over the years. Most OEM wire sets up until a few years ago were 7mm and worked just fine. The car manufacturers recently jumped on the bandwagon with 8mm and 9mm plug wire sets coming stock on your new vehicle.
Racers have been upgrading from 7mm to 8mm for decades and for good reason. Years ago with the junky 7mm stock carbon wire sets, when you upgraded your ignition system to a better coil and distributor, then built the engine to handle higher RPM, you really needed some better quality in your plug wires. The older shielding materials did not do an optimum job keeping the spark in the wire. Plus, they did not have much help if you think about the cheap, old, stamped steel chrome wire separator kits with the cheesy grommets slid inside. Your spark from the coil is looking for the fastest way to ground, and you hope that is at the spark plug. Having a nice sharp edge of metal before the plug, that is right up next to the edge of the plug wire is very tempting. So tempting that the spark energy may use it instead, creating an under hood lightshow and corresponding misfire.
Now we're sitting here in the 21st century and technologies, materials, and manufacturing processes have changed. The hot setup right now is actually the Accel 5mm plug wire sets. These use their top-of-the-line 300+ spiral core with a 5mm thick, 550° High Gloss Silicone Jacket. These wires are great! We've tested them and they work perfectly on everything we've installed them on, from street and street-strip vehicles, to 1,000 HP drag cars. Accel is one of the Mr. Gasket companies, as is Mallory, so your getting some shared technologies. Plus, with these skinny, coffee straw looking wires, you have improved header clearance and easier installation in tight areas.
The other thing to consider is to just take a look at a Top Fuel dragster. 6,000+ horsepower and monster dual magnetos, but hanging over the engine are simple 8mm plug wires. They do add the Mallory Pro Shield Insulated Shielding, which is mostly for abrasion protection, since they are rebuilding the engine in a mad rush after every pass.
 Performance Ignition Units are a great upgrade if you are "really" upgrading your engine and vehicle combination or put your vehicle through driving styles that could use some ignition help (racing, towing, off-road, harsh climates ... "like you do not believe in tune-ups"). An electronic or capacitive discharge ignition will help your engine burn more fuel as well as give your engine the ability to safely reach higher RPMs (than it is designed to do so). The added output that the ignition unit tells the coil to give out will really help your engine survive longer, make more power, as well as lower emissions, and be consistent in winning races. You can gain in performance with an aftermarket ignition control in efficiency, faster starting, smoother performance, higher RPM, and lower emissions.
Electronic Timing Controls and Retards serve as an added feature to making sure that the timing curve is "exactly" what your engine demands to make maximum horsepower and torque and prevent engine damage when using high power engine upgrades such as nitrous, superchargers, etc. Electronic timing controls in many cases give you full computerized programming capabilities of your timing curve, eliminating the sometimes binding and inaccurate mechanical advance controls. The timing retards allow you to select degrees of retard based upon your engine demands. From a high speed retard (your engine needs a bit less timing in many instances in racing applications at high RPM or top gear), to retarding the timing based upon the amount of boost from superchargers to the use of selected retard settings upon activating a nitrous system. This retard also works well l as based upon exceeding normal engine loads or fuel quality in street use towing applications to eliminate engine damage from detonation and other occurrences.
What Are Timing Retards and Controls?
Timing controls and retards are just what their name implies. A timing retard is an electronic device that retards the timing at a specific or controlled RPM, or event (such as a gear change, or nitrous activation). A timing control is typically an electronic device that controls the timing curve or rate of timing at a given RPM, but it can also be an ignition amplifier.
Some of these devices are controlled by resistors (chips), others are controlled by computer electronics, and some are manually controlled by the simple turn of a dial by the driver.
Here is a post on a mailing list where the user asked the question about finding TDC on an engine and requesting help on some general timing problems.
This was my response to the post.
To find "exact" TDC you need a few tools and some basic knowledge ... I can give you the knowledge here.
The fastest way is to use a piston stop and the degree wheel you use to degree in your camshaft. Here's how:
- Mount the degree wheel on the balancer with the correct turning tool to be able turn the engine by hand. Also, mount a pointer on the block that will identify the numbers on the degree wheel.
- With the cylinder heads on the engine you will need to use a piston stop that screws in the spark plug hole. It does not matter exactly how far in the cylinder you go just so long as the stop is secure and will contact a flat spot on the piston, try to stay away from any machining edges. In most cases you should not have a problem. If the heads are off you can use a plate-style stop or a dial indicator.
- Spin the engine slowly "by hand" clockwise until you contact the piston against the stop. Write down the number you see the pointer aimed at on the degree wheel.
- Spin the engine counter-clockwise until you hit the stop again. Again, write down the number the pointer is aimed at.
- Now what you do is find the center of these two marks ... the leftovers... (it is usually pretty easy to just split the difference on the wheel).
- Remove the stop and spin the engine to the correct TDC point on the degree wheel.
- You now mark your balancer as "0" on your balancer at the zero mark on your timing tab. (This would also be the place to set zero on your timing tape if you decide to use it.)
Now, for setting your timing ....
Hopefully you are using a quality Advance Timing Light ... these are the expensive ones with buttons or a dial (if you do not utilize a Advance Timing Light, the correct degree tape for your balancer diameter is the way to go) that you can always "shoot zero" and read the timing on the light. This is the best way to see what your TOTAL timing is at and exactly at what RPM it is in by.
Example #1: You want 12° initial timing, so you set the timing light to 12° and shoot to the zero mark on the tab and balancer. Adjusting the distributor so that you have flash at "0" degrees is actually 12° based upon what you have set the timing light at.
Example #2: You want to know what your timing curve is really set at. You can do a step-test which is when you can write down each timing setting at a given RPM (usually 300 or 500 RPM increments up to full advance RPM). Run engine to 1500 and adjust timing light to where you see ZERO on the balancer --- write down the number on the light. Spin the engine up to 1800 RPM and adjust the light to where you are again at ZERO on the timing marks --- write down the number on the light. With these numbers you can plot and change your timing curve to where you want it by either the weights and springs in the distributor or with electronic timing controls.
The timing you had set at 36° Total Timing should be a fine starting point. What you need to be aware of is that vacuum can and what it can do to your settings.
There are two types of vacuum advance functions available:
- One uses a PORTED vacuum source that as RPM increases, so does the vacuum to the port .... this is a BAD connection in Racing, especially since we typically retard our timing at the upper RPM levels. But it can be used as a tuning tool so long as you do not exceed the MAX total timing figure you need. In this case you will be using the vacuum advance as part of your total timing.
- The second uses FULL MANIFOLD vacuum, which is how I prefer to use vacuum advance (street cars only). Some may disagree, but it works for me! To do full manifold mandates an adjustable vacuum canister on the distributor. The way this system works is when you smash the throttle and vacuum levels go to atmospheric the vacuum advance is stopped. No ping, no excess unneeded timing that is only good for street car efficiency anyway.
In a TRUE racing environment, vacuum advance is not needed. You will typically run an ignition control with FULL advance on all the time. You then use a start-retard and various timing controls for retarding at high speed or at the initiation of a Nitrous solenoid to get the curve the way you want it. In most racing applications a timing curve is not needed.
Think about it ... we stage our cars --- bring the RPM up on the converter (or clutch in, RPM up in stick cars) --- light turns green and
throttle goes to the floor. How often are we in the curve of a car that has all the timing in by 2500-3000 RPM? A split second at the most? That is for most of use ... someone with an 18-Second racer will obviously disagree.
Newer experimentation and available ignition controls are giving us programmable ignition units that through our PCs or an independent
controller allow us to change the timing map at any given RPM or load (vacuum sensor) to get the optimum timing curve for each individual engine. Many have opted to skip these controls by virtue of their complicity or cost, not to mention that you will need a lot of seat time to make beneficial changes or a chassis or engine dyno to do it right with "hard number" measurements.
Examples of these units are Holley Annihilator which is very thorough but a pain to make changes. Mallory now offers the Hyfire VI, Hyfire VI-A, Hyfire VI-AL, and Hyfire VIIC ignition control units.
After you get the advance curve, correct timing marks and vacuum advance to behave, you will need to experiment with actual "initial" settings for best off-line power and then the "total" timing number for the best top-end charge.
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Mallory Hyfire VII-CR
#667CR
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Mallory HyfireVI
#685
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Mallory Hyfire VI-AL
#6853M
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Mallory Hifire Nitrous 6
#6865M
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