IGNITION TUNING FOR STREET HIGH PERFORMANCE (classic distributor ignitions)

(This is a compilation of knowledge sourced from experience, automotive industry practices and technics)

TUNING YOUR CLASSIC DISTRIBUTOR IGNITION SYSTEM TIMING MARKS MUST BE VERIFIED AS ACCURATE

Total timing is what a motor needs to produce its maximum horsepower and torque. Initial timing allows easy starting and lower idle speeds. Want to learn a little about the factory ignition timing, why it is what it is and how it can be made to perform better? Believe it or not, there is a lot of performance hidden in your stock distributor’s ignition timing and advance curve.Take a look at the chart on the right, it shows what a typical factory specified ignition timing looks like. The left side of the chart shows the degrees of timing, the bottom of the chart shows the RPM. The factory ignition timing in this example starts at 8° BTDC at about 700 RPM for its Initial Timing. As the RPM increases, so does the timing increase (this is the Advance), until it plateaus where it reaches its Total Timing of 30° at about 4200 RPM. This is a typical factory timing curve.

Most factory distributors have about 22° (+/-) of mechanical advance. 8° Initial timing + 22° mechanical = 30° Total Timing. The factory timing will give acceptable performance and operate on lower grade gasolines. Also the lower timing limits horsepower/torque minimizing drivetrain component fatigue, lowering operating costs through the factory warranty period.

However, high performance is different. We want our motors to run at their best. If that means buying better grade fuels, preforming tune ups more often and repairing fatigued parts then so be it. Why settle for mediocre factory performance when we can have HIGH PERFORMANCE. And, one of the tricks to high performance is to set your ignition’s TOTAL Timing. Another trick is to adjust the mechanical advance to come in sooner. Total Timing and advance curve adjustments, when done correctly will allow the motor to produce its maximum power and performance.

As teenager growing up in the 60’s, I learned early on about increasing timing and getting more performance. In my youth it was more of a trial and error process, we’d increase the timing until it pinged/rattled and backed it off until it didn’t. Then when a friend of my father explained mechanical advance curve changes and how it effected performance, a whole new world opened up. It didn’t take long before we were adjusting timing and advance curves for all our friends too!

With a stock distributor, we set the total timing where the motor performs its best and let the initial timing be whatever it ends up being. Remember, initial timing isn’t performance, total timing is where the performance is and total timing is when the advance curve is all in (we’ll talk more about the curve in a moment). Take a look again at the chart above, follow the advance as it climbs then levels off at about 4200 RPM, where it levels off (plateaus), this is where the mechanical advance is all in (peaked, does not advance anymore), this is where Total Timing is. Again, look at the chart above where the timing starts to rise (about 1200 RPM) and reaches its maximum at about 4200 RPM, this is the Advance Curve. While this curve is acceptable for factory performance and low octane gas, for high performance it is too slow and sluggish. For high performance we want the curve to start early and finish fast, a quick curve will produce maximum low end and performance.

Learning how to set total timing and adjusting the advance curve will unlock a tremendous amount of performance in your motor. Even a stock motor will benefit. Today the process is a little more refined than it was when I was teenager. The guess work is gone, we know exactly where the timing targets are to adjust for the best safe ignition performance.

Plus, it’s easy to do! If you’ve ever set your factory timing and can read a tachometer you can do this!

If you have an adjustable timing light GREAT! If you have a standard timing light it will work too, you just need to get some timing tape to go along with it (https://www.summitracing.com/parts/msd-8985/overview/). I’ll show you both methods, either will achieve the same thing, the adjustable light just makes it a little easier. Accurate motor timing marks are essential to success. Motor must be in good operating condition. Distributor and its mechanical advance must be operating correctly.

Before you go any further, your timing marks must be verified as accurate, see Easy way to verify T.D.C. & timing marks.

AND, PLEASE BE SAFE: Secure any loose clothing, wear safety glasses and any other safety gear necessary.

Page � of �1 3

10°

20°

30°

40°

1000 2000 3000 4000 5000 60000RPM

DEGREES

FACTORY

TOTALTIMING

ADVANCE

INITIALTIMING

The chart to the right shows both the factory timing (blue) and the new high performance timing target (red) we’ll be adjusting too. Note that increasing the Total Timing has also increased the Initial Timing as well. This will bring your idle speed up and you’ll need to adjust your carburetor’s idle speed down a little when your done. The increased Total Timing will give you a LOT more performance. The increased initial timing will usually cool the motor at idle better and add a little more throttle response to your carburetor. The downside is you will probably have to run premium gas. These are tried and true safe timing adjustments, when done correctly it will boost performance without harming your motor. Disconnect the vacuum hose going to the distributor and plug the hose going to the carb (vacuum advance must be disconnected and plugged off at the carburetor). Block your tires so your car can’t roll, set your brake and place your transmission in park (neutral if manual transmission). Warm your motor up, lets get started. USING AN ADJUSTABLE TIMING LIGHT TIMING TIMING MARKS MUST BE VERIFIED AS ACCURATE

Set your adjustable timing light dial to 36° (aluminum heads set at 34°). With your motor off, loosen your distributor till you’re just able to turn it, and start your motor. Bring the motor speed up to 3500 RPM, read your timing marks and adjust your distributor to read 0° (the adjustable light has 34-36° already dialed in). Now take it to 4000RPM it should still read 0. If it still reads correctly at 4000rpm GREAT! If your timing moved when the RPM increased, go to adjusting the advance curve and repeat total timing after curve adjustments are completed. Tighten the distributor. Bring the motor RPM up while watching the timing marks, slowly increasing the RPM until the timing reaches 34-36°. Note the RPM when the motor reached its total timing (34-36°), this is when your advance curve is all in. If the advance was not all in by 2400 - 2800rpm, go to adjusting the curve and check total timing again after. Let the motor idle, adjust your idle speed to 600-700RPM (as low as possible), initial timing must be checked at below 800RPM or you risk reading partial mechanical advance and an incorrect reading. Once your idle speed is adjusted check your initial timing, it should now be 12-14°. Go for a test drive, leave vacuum advance disconnected at this time. Listen closely as you accelerate hard to WOT (wide open throttle), any pinging/rattle/marble sounds? If yes, retard the timing 1° and try again. If pinging/rattle/marble sound remains, retard 1° at a time until there is no pinging/rattle/marble sounds when accelerating to WOT. Once the timing is correct, write it down for future reference. Reconnect your vacuum advance take it out at cruise speeds with slow accelerations, if vacuum advance causes pinging/rattle sound at slow or slight acceleration from cruise speed, the vacuum advance will need to be adjusted or limited (see, check vacuum advance below). Reset your idle RPM to your desired speed and continue to adjusting the advance curve.

USING A STANDARD TIMING LIGHT TIMING MARKS MUST BE VERIFIED AS ACCURATE

Apply the appropriate timing tape to match your balancer (https://www.summitracing.com/parts/msd-8985/overview/ ), and hook up your standard timing light. With your motor off loosen your distributor till you’re just able to turn it, and start your motor. Bring the motor speed up to 3500 RPM, read your timing marks and adjust your distributor to read 36° (aluminum heads set at 34°) on the timing tape. Now take it to 4000RPM it should still read 34-36°. If it still reads correctly at 4000rpm GREAT! If your timing moved when the RPM increased, go to adjusting the advance curve and repeat total timing after curve adjustments are completed. Tighten the distributor. Bring the motor RPM up while watching the timing marks, slowly increasing the RPM until the timing reaches 34-36°. Note the RPM when the motor reached its total timing (34-36°), this is when your advance curve is all in. If the advance was not all in by 2400 - 2800rpm, go to adjusting the curve and check total timing again after. Let the motor idle, adjust your idle speed to 600-700RPM (as low as possible), initial timing must be checked at below 800RPM or you risk reading partial mechanical advance and an incorrect reading. Once your idle speed is adjusted check your initial timing, it should now be 12-14°.Go for a test drive, leave vacuum advance disconnected at this time. Listen closely as you accelerate hard to WOT (wide open throttle), any pinging/rattle/marble sounds? If yes, retard the timing 1° and try again. If pinging/rattle/marble sound remains, retard 1° at a time until there is no pinging/rattle/marble sounds when accelerating to WOT. Once the timing is correct, write it down for future reference. Reconnect your vacuum advance take it out at cruise speeds with slow accelerations, if vacuum advance causes pinging/rattle sound at slow or slight acceleration from cruise speed, the vacuum advance will need to be adjusted or limited (see, check vacuum advance below). Reset your idle RPM to your desired speed and continue to adjusting the advance curve.Never increase initial timing without checking total timing or risk detonation (pinging/rattling, bad for the motor). Always lower Total Timing if pinging/rattling (detonation) is present under throttle load.

Page � of �2 3

10°

20°

30°

40°

1000 2000 3000 4000 5000 60000RPM

DEGREES

NEWADVANCE

INITIALTIMING

NEWTOTALTIMING

ADJUSTING THE ADVANCE CURVE TIMING MARKS MUST BE VERIFIED AS ACCURATE

Mechanical advance (also called centrifugal advance), works by the centrifugal force generated from the spinning distributor. Inside the distributor are weights that operate a cam. The weights are held back by springs, as the RPM rises the distributor spins faster generating more centrifugal force overpowering the spring tension forcing the weights outward rotating the cam which advances the timing. The combination of weight ratio to spring tension determines the amount of time it take the weights to reach their maximum travel, advancing the distributor its furthest. This is called the advance curve. Adjusting the advance curve can give the motor more punch (low end). Changing from the factory curve to a high performance curve will usually surprise people when they experience the difference.When you were setting total timing, if the timing moved when you increased RPM from 3500RPM to 4000RPM the advance curve needs to be adjusted. If the advance curve was not all in by or before 2400-2800 RPM the advance curve needs to be adjusted. It’s not hard to adjust the advance curve, you just need a “distributor advance kit” to fit your distributor. Kits usually contain new weights and variety of springs and bushings for your distributor. Usually we only need the springs to re-curve the advance. Order the kit and we’ll get started. https://www.summitracing.com/search/part-type/distributor-advance-kits?ibanner=SREPD1Remove your distributor cap and rotor exposing the weights and springs inside your distributor. We are going to be changing the springs that hold the weights in. At this point we will only be changing

the springs, keeping the factory weights to achieve our new advance curve. The original weights unless worn usually work best and the bushings are usually not used unless you need more initial timing for a big cam (a subject for another day). Lay your new springs out on your bench, arrange them left to right with lighter

springs on the left progressing to heavier springs on the right. At your distributor, remove one spring only, and set it above the closest corresponding new spring in the kit. Match it for size and length, this will most likely be a heavy spring. Replace this one spring you removed with the lightest spring in the kit. You should now have one heavy (original) and one light (new) spring in place in your distributor. It’s OK to mismatch spring tensions to adjust your curve, it’s a standard practice. The weights working against the cam will equalize the tension and it will not hurt a thing. It’s how we fine tune the advance curve. Sparingly lubricate the advance pivot pins with a drop of 10W motor oil and put your distributor back together. Hook your timing light up (disconnect and plug your vacuum advance). Starting at idle, slowly increase the RPM while watching your timing mark or timing tape until you reach the point where the timing has reached it’s max total timing and moves no more (plateaus). Note the RPM where it reached total timing. Preferably we want the total timing to be all in by 2400, no later than 2800 RPM. If the RPM is still higher than 2400 - 2800 when you reach total timing, replace the other heavy (original) spring with one size lighter (medium), and try it again. Keep adjusting springs until you reach your goal of all in by 2400 - 2800 RPM.Take a look at the chart to the right, it shows the factory and the new advance curve. Note how the new curve starts sooner and gets to all in faster. Don’t be afraid to experiment with the springs to get your advance curve where you want it, the sooner total time comes in the better, just listen for signs of detonation (pinging/rattle/marble sounds). If you hear pinging/rattle as you accelerate (vacuum advance disconnected), check total timing first to be sure it is correct, if total timing is correct, increase spring tension at the weights until pinging/rattle is gone.Take it out for a test drive. But hold on! You’re gonna have a lot more low end punch than the factory gave you now!

CHECK VACUUM ADVANCE The factory used vacuum advance to help compensate for lower total timing settings. With your new timing it may add too much now. Read your initial timing at idle and write it down. Connect the vacuum advance to a manifold vacuum source, this will increase idle speed don’t be alarmed, just temporarily lower your idle speed back down where it was. Read initial timing at idle again. At idle, manifold vacuum is at its highest and the vacuum advance will be at its greatest. Note the amount of advance that has been added to your previous initial reading. If needed, adjust or limit the vacuum advance to 10 - 12 degrees maximum. This may require an adjustable vacuum advance kit (https://www.summitracing.com/search/part-type/distributor-advance-kits?ibanner=SREPD1). If you hear pinging/rattle at cruise speeds with slight acceleration, lower vacuum advance until pinging/rattle is gone.Believe it or not, vacuum advance has nothing to do with HIGH PERFORMANCE. But rather, vacuum advance is an ECONOMIZER, used to compensate for the factories lower specified total timing. The vacuum advance raises the timing up at cruise speeds, it allows the motor to operate more efficiently and saves fuel at cruise speeds. At WOT (wide open throttle) or under power the vacuum decreases to near zero (remember vacuum windshield wipers), the vacuum advance is negated (off). Often, once total timing and the advance curve are adjusted very little vacuum advance is needed and in some cases none at all. Stay tuned my friends, there’s more horsepower under the hood! Enjoy!

Page � of �3 3

LIGHT MEDIUM HEAVY

Advance CamAdvance Spring

Advance Weight

10°

20°

30°

40°

1000 2000 3000 4000 5000 60000RPM

DEGREES

NEW ADVANCE CURVE