How Ignition Timing Works: Vacuum and Mechanical Advance Explained! 

Why can’t everyone make videos this easy to understand as well as informative

That's probably the best explanation on You Tube .

Been messing with cars since the 60's, and I never fully understood the function of vacuum advance until this video. THANKS!!

That was actually a very thorough explanation. I feel like I could build an ignition system from scratch.

Thanks for making this video! Answered a lot of my questions

This is the first man to mention the adjustment of the vacuum advance, made in the vacuum advance device,,,, common practice back in the day

To me, one of the main reasons for running vacuum advance is longer engine life. Burning ALL the fuel means there will be much less fuel to wash the oil off the cylinder walls. This results in much longer piston ring and cylinder wall life, and also drastically reduces oil dilution which isn't great for the bottom end.

Being a driver & not a mechanic I appreciate the basic knowledge of what is happening under my hood. My friends are drag racers as well as mechanics so I know enough to leave shit alone and let them dial me in. Went with the MSD equipment that they all use. Been real happy that I spend more time driving without constant tinkering. Thanks from a dummy ;-)

It's cool to see the Liberty Mutual car in a RU-vid video about ignition timing!

Very simple and easy to follow. Thank you.

One of the best explanations out there.

Good video MSD definitely worth watching! Unity Motor Sports Garage also has two excellent videos on vacuum advance with David Vizard on how to set up your vacuum advance, anyone wanting to get the best out of their street motor needs to watch them!

you are the only one explaining this the way for me to understand. ive been disconnecting the vaccum advance hose because i thought it gives the engine too much timing (up to 60) at cruising speed. thank you!

Excellent explanation! Thank you!

Fantastic explanation. Well done👌🏽

Good info.Hard to explain but the electrical firing of a spark plug is already there ready to fire and does not have to travel through the wires at all. Electricity does not travel. If it had to it would take time to get from the power plant to our house then to the light when we flick the switch. It’s instant. No lag time. Because it’s already available! It happens in less than 1,000’s of a second. It’s how 8 plugs can fire at 7000 rpm almost instantly. But advancing the timing just makes sure it all happens when it needs to. We do have to speed up the process to stay in sync with the engine requirements. Again. Good info.

Perfect explanation ! Thx

Very clear and informative video! I did not expect it to be this good.

Great content, Very well spoken and explained. Thank You

Give this guy a raise!

Excellent video. Well done.

Fantastic video. Just got 67 mustang, trying to learn what I can.

Very good video, well explained.

Great presentation loved it. Just wondering, if I am running a SNIPER EFI and I use timing control Hyperspark with CDI, can I or do I have the chance to run advanced/ Lean setup in cruise/ part throttle conditions???? It seems that Vacuum advance is much better than my current Mallory Mechanical advance system. Would love the have best of both worlds. Again this really taught me alot.

Because this video was so informative, I will look for MSD products from now on. I appreciate companies that makes their product's info as good as their products..besides, red looks good in a chevy engine bay!

Others have commented on this but I'll try to be as succinct as possible. The need for ignition advance is entirely due to the time it takes for the fuel air mixture to burn completely. It may seem to be instantaneous but it is not in relative terms. Relative to what you say? Relative to the speed (RPM) the engine is turning. Keep in mind that the time it takes to burn the fuel mixture is more or less constant. In other words, the flame travel speed is the same at idle as it is at redline, so if ignition timing were set and optimized for idle the engine would outrun the flame speed of the combustion event and the pressure in the cylinder would peak well past TDC. Not optimal. That is what the centrifugal advance is for, it advances the timing as the RPM increases. Vacuum also advances the timing but at W.O.T. (A.K.A high load) vacuum of course goes away and the timing is retarded so as to avoid detonation. There are other factors that enter into the optimal number of degrees of ignition advance but for the most part it is dependent on the combustion chamber design which greatly affects how fast the charge burns. A fast burn combustion chamber was the main reason the DFV Cosworth V-8 became the most successful Formula One engine of all time. Prior to the creation of the DFV, most overhead cam engine designs used very wide angles between the intake an exhaust valves which allowed for very large valve heads and large quantities of fuel and air to enter the cylinder. But to get the compression ratio high enough to take advantage of high octane fuels required very high dome pistons. That made for a very thin and slower burning combustion chamber, which required a lot more ignition advance than faster burning designs. Put another way, it is better to burn the charge fast and more completely than it is to try and stuff more mixture into a less efficient combustion chamber.

Thanks, lots of great info

This video was awesome

Wow that taught me a lot thank you

That was awesome 💯

Wire/spark time... try 3 nanoseconds. Don't ever worry about that, ever again. The engine can't turn fast enough to get at a 1% error in time of arrival [coil field collapse origin to spark appearing in the chamber] over the full operating range. If it was that twitchy, an oscilloscope, not a wrench, would be the tool for timing changes The big confusion is always vacuum advance. Mechanical advance corrects for the rpm range in use, while vacuum fine tunes that for intake conditions. Passing through 2200 rpm at 1/4 throttle is a diffferent thing than at 3/4. Vacuum will prove it every time Racers lockout advance in their distributor, but they are running 4k stall converters or higher, so the need to manage spark timing under low rpm with a load can be waved off. So time to examine combustion: flame front speed on an air fuel mixture is pretty much a fixed value, but... engines run varying rpms. so altering timing is what works for managing performance. It's not that combustion takes more time to complete, but peak pressure happens with piston further down the bore as rpms go up and if nothing is done - lost power. It takes changing fuel to change flame propagation speed as a general rule. So, vacuum advance: manifold or ported vacuum? Short answer is use what the distributor was designed for - the two modes are not really interchangeable. For ported, as signal increases, advance increases to fill a range before mechanical advance is all in [effectively taking over] - sensing is near the bottom of the carb venturi, which means velocity can add to signal. For manifold, a decreasing signal allows advance. And while manifold signal [having fewer restrictions] tends to be stronger numerically, the inverse function could be problematic in the case of an aftermarket cam swap - diaphragm design might need revisiting on account of sensitivity being in the wrong area [or even out of range], and it is largely divorced from velocity. Ported is my personal preference: just easier to live with most configurations where street use is the aim, but that admittedly takes a number of carburetors off the table - don't ever toss an old 3310. Keep wrenching, and enjoy your ride... whatever it is.

Loved the video very informative,,,, thank you.?.

Very good explanation on timing did anyone else notice the MALLORY T SHIRT for a msd advertising 😀

Very cool, thanks.

Awesome answered everything I needed to know 🇦🇺🍺👍

a good explanation of VA.

Really informative video that is well written. The only issue is at the very beginning with the explanation of the time it takes for the spark to reach the spark plug. True that the electric field takes time to build to create the high voltage spark, but this is trivial compared to the time for the combustion event to take place. The rest of the time mentioned with power flowing thru the wires happens at the speed of light (literally) so that time is zero compared to the other delays that create the need for advance.

Cool part!

it’s amazing how an engine really runs and works and how the vacuum advance system really ads fuel efficiency.

Good stuff.

Now on to the ported vs manifold vacuum supply for the advance debate?

Gr8 video

All the things I thought I knew about VA were totally wrong. Thanks for the clear and concise explanation. So does vacuum advance go away with computerized MPI scenarios?

Thank you.

Awesome Explanation! Can Anyone tell me if a VA would be a good idea for my SBC Powered Street Car when I only use Nitrous at the track?

Indeed sr I like how you guys just ram information in the ear 👂 well played msd. I dig yer products. I'm goin atomic....

ive learned something today

on my 318 rebuilt I'm running stock pistions , rods and crank and stock heads , edelbrock intake and 600 cfm. I'm using an Erson cam - 0.050 is 214/214 lift is .449/.449 and lobe Sep is 112. I'm running a mopar electronic distributor with vaccum advance . this truck has 3:55 gears . do need to be running full vaccum on the carb or on the timed port? I used 2 different vaccum gauges after engine is fully warmed up and in the green zone = best fuel milage I got real close to 20 on the intake vaccum . took it for a test drive ran awsome down the road and highway but would barely start to ping under load after taking off from a stop or up a hill so I backed the timing down a degree or 2 till I didn't here the noise anymore . I think I'm still some where between 15-20 on vaccum . it won't do burnouts unless on a sooth surface and won't roast the tire from a dead stop with foot off the brake ??? the carb is set at factory spects except for the metering springs and they have been matched to the vaccum of the intake say 17 ÷ 2 = 8.5 and then match up the colored spring closest to the final number . I have checked everything = fuel supply and pressure spark plugs and wires and coil . air filter as well and the distributor has been set up for my engine combo, vehicle weight , gear ratio ect

I've heard a lot of guys say the hot ticket on a street performance pump gas N/A application is more initial than mechanical, all in at 2500 with no more than 10 degrees added for vacuum advance a rule of thumb Sounds like a need an E curve for my 302 windsor :)

Ported or manifold vacuum for vacuum advance? I've seen arguments on YT & I'm leaning towards David Vizards manifold theory & tuning strategy, very scientific & promotes maximum fuel economy on street/strip engines.

Igniter vs Points distributor vs HEI I have a 1990 Lincoln Town with the Windsor V8. Looking for tune-up advice, how to get the best fuel efficiency. upgrading does sound like less maintenance but questioning ROI Return On Investment? btw the car has sat for 8 years and running well on warm days. but if I don't let it warm up 20* F or colder and try to drive off after 10 min it seems rough until it gets to operating temp. also after 45 to 1hr idle to op temp. it will kill the motor most of the time when I change gears R or D. I haven't noticed during warmer days dying during gear change but I have only had it for three weeks.

Wow more timing for the lean mixture that one blew my mind

Thanks

It'd be great to see a video like this but with the m s d 6 AL Digital 6530 model, running a locked out distributor and using a map sensor to add timing when you're cruising at highway speed with an n a motor

Hey how you doing ? I have 67 mustang 289 and instal distributor msd + msd ignition box I instal all and no Spark Plug in the cylinders and when I instal the old distributor it's works. What's the problem you think ? Thank you

I have buddy with a SB Chevy. Because the firewall is veey tight in back of engine he runs a Mallory small cap drist. without vacumm advance. Any tip on timing that setup?

Can the mag pickup be replaced on the distributor without having to remove the distriburor from the engine???

The electrical signals and the actual current that causes the spark travels at 186,000 miles per second. The time for the spark to reach the spark plug is measured in millionths of a second, not thousandths. The reason for advancing timing is to allow for the flame front of combustion to arrive at the piston top at the proper time in the piston’s travel. This flame front travels at a speed very much slower that the electrical spark. This is why fuel octane ratings are important. To insure that only the spark plug starts the combustion.

Do we use or not use vacuum advance on a blown 383 with msd 6al-2 programmable?for 8.7:1 comp ratio. I want 26 initial and 34 total..?

Wonderful presentation! Just wondering - why is the electrical signal being sent to the spark plugs so slow? It seems like the spark would be practically instantaneous

Great video, What about street/strip cars that are very very fast that you take on the occasional cruise night. Vacuum advance or stick to mechanical?

For parade idling, you NEED! VAdvance!

From the Chi Chi ignition switch the nearest Mr. Denis did you see condition the starter to start the vehicle over what wires go where

A question so I need a vacuum advance on my distributor I have a 390 engine msd and electronic distributor.

I purchased a Chevy crate 5 years ago for a 77 Monte. 480/460. 750 Quick Fuel carb. They shipped it with mechanical advance with the vacuum advance crimped. My Monte runs like a bat out of hell. 700/R4 tranny with overdrive. Cruises 75 MPH at 2,300 RPM with 3.73 rear. Idles in drive at 650 RPM smooth as silk. Other than MPG, is anything wrong with this setup? Trying to learn.

Okay so for a mild camshaft of 288 480 in a 350 .30 quadrajet fueled motor 2200 stall 700r4 transmission. Street or strip build I would run the ported side of the vacuum and when at the strip just pull the vacuum advance hose off???????????? Yes I am this dumb. I would appreciate any help

Why does the msd instructions state to install the vacuum to a ported source above the throttle blades?

Electricity flows at the speed of light, No measurable delay from that.

MSD have an idea for distributors where old style engines could have fuel injection and spark control.

Wow is that an actual 70 AAR, or tribute car ? Cuda's are so freaking sexy and still looks hot, either way 😍

isnt that after atdc if the engine is rotating clockwise? when you explain that most engines run 12-15 degrees?

Ive read a hundred times MSD stating there canister coils to be mounted in an upright position , yet on the MSD channel they have it mounted laying down. Hmm very interesting.

So when you set initial and advanced timing do you set it with the vacuum in or plugged?

I installed an HEI at TDC and set the timing to -10BTDC on my 300 6 F150. Now it’s driving like I have a totally different gear ration. Insanely high RPMs at 45mph now, so I can’t drive on freeway. If I advance more, it gets worse. Better acceleration, way more heat. Retarding it fixes the heat issues, but i can only go so far before I lose so much power I start stalling everywhere.

Please explain why a 350 chevy with hyperutechtic flat top pistons, mild cam, vortech heads and valve assembly with an HEI ignition set @ 12* btdc pings at any kind of uphill or small load only when VA is connected. Engine runs great and quiet once VA is disconnected. Been running VA disconnected for years and engine runs great with awesome burnout power. Engine originally dyno @ 420hp/390trq..

Does fuel injected cars keep the air fuel ratio same on low or high throtle..??

One correction, the adjustment made to the canister with the allen wrench affects the rate at which the timing is increased, not the amount of degrees. That number is a fixed amount based on the stops on the arm, and the number stamped on it. Also, the source should come from a ported supply since the extra advance is unnecessary at idle.

I run MSD systems on all the cars that I work on, the programmable systems are great. Having said the first few seconds of this video are nonsense, you want peak cylinder pressure at 14-20 degrees ATDC not at TDC. The reason being that at TDC the gas pressure can not create ANY torque at the crank because the con-rod is vertical, the likes of Riccardo Engineering worked this out many years ago and it still holds true today. The reasoning for the bob weight advance was misleading, it does not take longer to burn the mixture as the revs go up, in fact due to turbulence the opposite is true, the problem is that the crank will have turned more degrees as the RPM goes up during the time that it has taken to burn the mixture. The explanation for vac advance is also not very good, OK so the leaner mixture may have a very slightly slower burn rate but that is not why we need more timing at low loads. At low load the volumetric efficiency of the engine is very low (low VE). A low VE leads to a very low initial cylinder pressure because there is hardly any fresh charge in the cylinder to burn (and there is probably a load of exhaust gas in the cylinder too since the piston will have an easier time pulling exhaust gas back in the the cylinder rather than pulling fresh charge through a virtually shut carb or FI butterfly). Low pressure BEFORE the plug fires leads to a slow burn rate so in order to get peak cylinder pressure at the right time the plug needs to fire earlier in the compression stroke. This also explains why if you raise the compression ratio in an engine you may need to pull back the timing a couple of degrees, you have raised the initial cylinder pressure and hence increased the burn rate. Also what about ported and non-ported vac timing? (ported for emissions reasons and not really what the engine wants). Come on MSD, your ignitions system are great (although you need to make your bob-weight springs out of a better material, they corrode away after a couple of years! Luckily with the programmable systems the dizzy is 'locked out'). Anyway you can do better than to create a video with so many errors in it!

I have mechanical advance now on a Chevy 350. Can I just add a ported vacuum line to my distributor? There's no vacuum line connected to it now, thanks for your time 🤜🤛

🖤🖤🖤

The time it takes for the spark to get to the plug is negligible...its all about the time it takes for the fuel to burn compared to how fast the piston is moving...

Does the vacuum advance work at idle as well????

This ignition timming is for carburetor cars..??

This is a great explanation, but I still don't understand if you can 100% complete your setup pretending you'll never have vaccuum advance, and then just reconnect the vaccuum, or does the intent to include the vaccuum advance alter any mechanical choice (initial, bushing+spring) you make.

So do you want your total advance with vac or not

Now do one for locked out distributors. Not how to lock it out. Let's see how to set the engine timing, and carburetor idle.

The engine diagram for the Buick 401/425 Nailhead is wrong. LHD car passenger side front to rear is 1,3,5,7. Drivers side front to rear is 2,4,6,8.

I can’t wait to see the in-depth operational, engineering, manufacturing, considerations with schematics that train the listener on everything to do with an ignition system starting with the battery and the key switch. How about it?

Not true that at higher RPM the combustion slows down. Its that combustion time stays same but piston speed increases giving the combustion less relative time to complete, so you need more advance.

vacuum advance is because the fuel atoms are further apart . This takes the combustion flame front longer to travel across combustion chamber . A street car is not a race car . On the street vac advance is needed . light throttle cruise is between 35mph to 55mph . You need to measure the trigger point in inches of Hg Vacuum advance should ramp up between these 2 points under light throttle conditions . When moderate throttle is applied the vacuum advance should disappear mechanical advance resumes

I still don't understand how the springs work and how to know what one's to use.

The FireStorm Plasma iPlug is a new entry in the formerly mundane area of Spark Plugs. All Spark Plugs produce "sparks" to ignite the Air Fuel Mixture in the combustion Chambers. FireStorm is different, it produces "PLASMA". By doing that, it eliminates the Catalytic Converter and EGR Systems and can still pass future emission requirements in California. Here is a clip: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-abwXApkLhbc.html Further testing after that clip was shot in Detroit proved a 70% savings in fuel all while affording a 125 More Horsepower. It is a Paradigm Shift in Air Fuel Ratio as this plug operates at 30 to 1 Air to Fuel Ratio. All current IC engines operate at 14.7 to 1 and require a Cat and EGR. FireStorm can even crack water right in the Combustion_Chamber thereby eliminating so-called HHO Generators. Can I hear fill your car up at the side of your house with the garden hose? YES!!!!

Either tune ignition Advance towards MBT as long as you're not knock limited on fuel octane, or dont waste my time lol. Ever seen so much positive manifold pressure that 0tdc ignition was acceptable and still made tq? Unreal

Is Holley actually going to bring back Mallory?!?!? You’re wearing a Mallory shirt, and your channel is MSD, and both are owned by Holley now- so….. please say you are going to revive Mallory !

Did I miss something? I thought Mallory and msd were two different companies. This guy's got a Mallory ignition shirt on and doing a infomercial for msd..

I have an MSD distributor with no vacuum advance. He didn't explain how those work.

MSD channel but the guy talkin is wearin an Mallory Ignition shirt.......surely I am not the only person to notice this.

I guess we're just going to completely forget about idle then right??.......

Like the hot engines displayed in the video the presenter’s delivery is so fast. For the novice a clearer demonstration of what happens inside the distributor would be helpful. Maybe if I watch it a few times I might understand how vacuum advance works. But thanks anyway.

Im having problems with my truck at idle souds great but in gear driving only wants to bog out i have to drive super slow if i gun it it does one back fire and thin snaps out of it if i advance it or retard it its worse ?? Carb is 600 holly ,holly intake but on 305 engine