Set Your Engine’s Ignition Timing

You just put your rebuilt classic car engine together and your adrenaline is pumping. Previously we discussed the proper procedure for breaking in a new or rebuilt car engine so now you are ready to rock-n-roll. Pump the throttle, turn the key, and… the thing runs like a total dog. It idles fine, but as soon as you step on the throttle, it slogs along like a sloth or starts pinging as though it is about to come apart. Yes, you have timing issues. So now it is time to focus on your engine’s ignition timing.

Though your problems are not that severe, not having your engine’s ignition timing in order leaves a lot of performance off the table. A few tweaks to the distributor can totally transform the nature of your engine. And if you read “distributor” and asked yourself, “Isn’t that some old muscle car thing?” this post may not be right for you, cause today, we are poking around old-school engines and no computer required.

What Is an Engine's Ignition Timing?

It helps to understand exactly what you are tinkering with before you go making changes. You can do some severe damage to your engine if you do not have the timing in line. So, what is ignition timing?

If you are familiar with the four-stroke engine cycle, you know that ignition comes from spark plugs. The spark plug fires once the piston reaches the top dead center (TDC), during the compression stroke for the combustion to send the piston back to the bottom of the chamber.

In the real world, the spark needs to happen a little sooner. The reason is that the fuel and air mixture do not burn immediately. So, you want to send the spark before the piston reaches TDC to ensure that the entire mixture is ignited at just the right time to send the piston down with the force of a complete burn. That is why an engine usually has an initial timing of something around 10 degrees advance.

What is 10 degrees advance, you ask? You have two primary settings to toy with, initial timing and total timing. Initial timing, or the 10 degrees we mentioned earlier, is your timing setting at idle. Total timing, which may be something like 34 degrees of advance, is what the timing changes to when the engine is up to speed.

The reason the timing needs to change is due to the increased speed of the engine. Despite the increase of piston speed, that fuel mixture takes the same amount of time to burn. For the mixture to generate force at the right moment, the spark needs to happen sooner.

If you just adjust initial engine’s ignition timing and ignore total timing, you are likely to run into issues. The reason is that the mechanical advance is going to bring in x-amount of advance. In other words, if your engine is designed to run with 10 degrees advanced initial timing and a total timing of 34 degrees, your distributor is going to bring in 24 degrees of advance no matter what.

That might not be important if you were to run a stock engine on older gas. Well, guess what, you changed your heads, cam, and added headers, all of which might like different things from your ignition timing, and even if you did not, today’s fuel likes a little more timing anyway. So, once you bump your initial timing up to 14-16 degrees of advance, your total advance runs out to 38-40 degrees of advance, and that is why your engine is pinging. You are going to need to mess with ignition timing no matter what and that entails a little more than twisting the old distributor.

Mechanical vs. Vacuum Advance

But before you go and pop your hood, hold on. There is still more to know before we get rolling. Timing advance on older engines is handled in one of two ways. The first being mechanical, which is managed by springs, weights, and limiters. The other is vacuum, which relies on the vacuum provided by the engine.

And many engines, like the 396 in my Chevelle, feature both. The vacuum advance is primarily in place to provide additional timing to increase fuel economy by providing a complete burn at light-throttle cruising speeds.

The thing about engine vacuum, however, is that it becomes non-existent when you stab the throttle, which is where mechanical advance comes into play. To better understand how this all works, we need to look at the anatomy of your distributor.

Inside the Distributor

First, you have a shaft that goes straight down to the camshaft, which turns the distributor to create your initial timing. Only, the shaft is not one solid piece, it is divided to allow the position of the rotor to move to create your total timing.

The mechanical advance controls the position of the rotor and, as the speed of the engine increases, a set of advance weights begin to move outward, which adds the additional timing advance. How far those weights travel due to the stops relates to how much timing is added. The springs that they are connected to control how fast that timing comes in or the RPM in which total advance is reached.

Vacuum advance comes into play after acceleration when you hit cruising speeds. The canister outside the distributor is also connected to the same shaft that the mechanical advance controls. As RPMs steady, and vacuum builds, the diaphragm within the canister is pulled forward, which adds even more timing. The additional timing it provides creates a cleaner, complete burn at cruising speeds.

Believe it or not, the vacuum advance adds a ton of timing. Sometimes as much as an additional 25 degrees. If you do not address the vacuum advance, you are likely to experience detonation while cruising.

That is exactly why a lot of folks decide to ditch the vacuum advance when they adjust their initial and mechanical advance—heck, you ever see a drag car with vacuum advance? That said, if you are working with a street-driven vehicle, you should keep the vacuum advance and adjust it so that you can achieve optimal performance at cruising speeds.

What Do You Need to Know?

Here is the thing, different automakers handle timing advances in different ways. While most engines from the olden days feature mechanical and vacuum advance, some use only use one or the other. You need to know what you have to work with

The advance weights move outward as the RPM increases

Not only that, but different distributors use different components to control mechanical advance. If you are running an HEI or MSD-type distributor, you are in luck. The mechanical advance is handled by weights that are attached to springs and bushings to limit timing and are located directly under the rotor. Swapping springs and bushings are extremely easy with this configuration. You still must do the homework to decide what springs and bushings you need, but the work is a breeze.

The rest of us, well, we are fending for ourselves. We still have weights and springs to work with but accessing them and providing limits to the advance weights gets a little crazy.

Take Chevy distributors, for example. We still have springs and advance weights to work with but to access them. We need to disconnect the distributor.

You will also want to get an idea of how much initial advance and total advance you need. Without a dyno, this can be a trick. An excellent way to get into the ballpark is to jump on some forums and see what others with similar setups are running. Keep in mind that your total timing usually will not change, just the initial timing and the RPM in which total timing is reached.

Engine Ignition Timing Safety

Shooting your timing and adjusting places you under the hood with a running engine. That means there is always the chance to gain a few scars if you are not careful. That said, you will want to use common sense and these safety tips to keep your tips.

Protect the soft stuff.Throw on some safety glassesand gloves. That engine is running, and your only human. Layers of protection never hurt anyone.
Steer clear of that fan. Your fingers and the wires of your timing light will draw toward that fan like moths to a flame. Be always aware of your position to prevent any accidents.
Yes, it is hot. You are not likely to accidentally grab a header while shooting timing, but you can always fall into a daze. Just play it safe and keep your wits about you to prevent burning yourself.

Everything You will Need to Time Your Ignition

Aside from the information overload we have already downloaded, you will need some tools to get the job done. Yes, there are some specialty tools and parts on the list, but they are not particularly expensive. Besides, any expenses are totally justified by the satisfaction of making some big changes to your engine’s dynamics.

Tool List

Timing Light
Wrenches
Plyers
Screwdriver

Part List

Mechanical advance kit

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting. You will also need a flat workspace, such as a garage floor, driveway, or street parking.

How to Shoot and Adjust Engine's Ignition Timing

Adjusting Mechanical Advance

Install timing tape/mark your balancer. The choice depends on your preferred method. In this case, we put timing tape to use.
Warm the engine up. Get the engine up to operating temperature. If there are any issues preventing an idle, including your initial timing being out of order, you should address them now.
Hook up your timing gun. If you are not running a wireless gun, simply hook the battery leads up and hook the pickup to the number one cylinder plug wire.
Loosen the distributor clamp. You will need to be twisting the distributor as you work, so the clamp needs to be released. You may need a screw drive to help initially start the distributer rotation if it is snug but be careful.
Disconnect the vacuum advance. Simply disconnect your vacuum advance line and plug the connection. A bolt or even golf tees are an easy source to plug the vacuum line.

Point and shoot. Position yourself so you have a clear line of sight to the harmonic balancer and your timing tab. Pull the trigger and pay attention to the number you see. In our case, we are looking for 20-degrees of advance for our initial timing.

Set your initial timing. Setting the initial timing is easy. Simply rotate the distributor as you continue to watch what number lines up with the timing tab on your engine.
Bring the RPMs up and record total timing. With the initial timing set, lock down the distributor and have a friend bring the engine RPM up. When the numbers stop increasing, you know what your total timing is. Record that number and have your friend verify the RPM in which that number was reached.
Kill the engine and adjust. Decide what springs you need to use to bring in total timing at the RPM that you want, and what bushings or other methods of limiting total advance you need, then adjust the distributor accordingly.
Start the engine and verify the results. Simply shoot the initial timing and total timing to verify your results after you have made the adjustments.
Take a Test drive. All that is left is to take it for a test drive to ensure the engine is running as you want it to. If not, repeat the process and try different adjustments.

Adjusting Vacuum Advance

In the case that you are running lean while cruising and not while accelerating, you know you have too much vacuum advance. Here is how to adjust it.

Break out the Allen key. Allen keys with t-handles are the best tool for the job. They offer better control and are much more comfortable to use. Each distributor has a different method to adjust so check your manual on the correct approach.
Disconnect vacuum line from the unit. You do not have to make this adjustment with the engine running, so there is no need to worry about plugging the line after removal.
Insert the key until you feel the keyway. This can be unsure as it is easy to go too far, and cause damage and you must feel around in there. It helps to use a bigger allen key to get an idea of where the keyway is, then gradually move down in sizes until you have found the right key.
Rotate counterclockwise to reduce timing. Most vacuum advance systems work by rotating counterclockwise to reduce timing and clockwise to increase it. You may want to verify with your own research, though.
Test and repeat. Take the car for a test drive. If you still hear pinging, simply repeat the process until it disappears.

How Do You Monitor Your Adjustments?

So, once you know what adjustments you are making and how to make them, all that is left is to read them. It is one thing to set the adjustments where you want them and assume they are in order. It is another to shoot the timing and know for sure.

All you need for this is a timing light and either a timing marker with some paint or a timing tab and some timing tape. Either way, your timing light works by connecting to the battery and the number one cylinder’s spark plug. Once they are hooked up, you just point the timing light on the harmonic balancer and take your reading.

At the very least, your harmonic balancer has a timing mark on it. That timing mark lines up with the timing tab to tell you when the spark plugs are firing. It helps to paint that timing mark with some white paint so that you can see it better as the engine is timing. As the engine speed increases, you want to watch that timing mark in relation to the tab to determine where your ignition timing is.

A lot of those older timing markers, only read out to ten degrees of advance. If you are in a similar situation, you’ll need to get some timing tape on the harmonic balancer to proceed. If you are using this method, you are watching for what number appears next to the zero mark on your timing mark. That number tells you how many degrees of advance your engine is running.

Tips to Adjust and Shoot Engine's Ignition Timing

Cam timing is a different animal. Advancing and retarding cam timing sounds similar and can have a similar impact on throttle response as ignition timing. But the reality is that they are two different processes.
Mark your balancer. Timing tape comes off. It is good practice to mark the location of the total timing number you desire with a notch and some white paint. That way, you can still double-check timing without timing tape.
Listen to your engine. Do not just go by what others recommend. Take their advice and try their tips. If they work, that is great. However, there is no universal formula, and you may still need to make some tweaks to the timing to please your engine.
Make sure your balancer is not worn. If your harmonic balancer is old and the rubber is worn, it will throw off your timing reading. Be sure to inspect the balancer to ensure it is not out of order before proceeding.
Faster is not always better. Bringing total timing in faster will boost your throttle response. At first, that seems great. But more power sooner can be harder to control on the street, which is why you should not just throw in the lightest springs. Try different springs or combinations until you find what you are most comfortable with on the street

Finally

Every engine will have different timing requirements based on its combination of combustion chamber design, compression, octane, cam timing, and ignition curve variables. The best way to determine your ideal curve is to make small changes and evaluate them for a few days of driving before attempting further changes. Pay attention to what your engine is telling you and record your changes in a notebook. Setting your engine’s ignition timing properly will allow you to get the most out of our classic car’s performance and drivability.