Timing Advance

[CZ-75]

Not yet... I will be soon, though.

 

[MechEng]

I'm glad I took a look at this thread. I just timed my engine to factory spec about 6 BTDC with no vacuum connected, and the car just hated life when it first started and ran right on the edge of dieing at idle. I'll have to go and re-time to 16-ish and see how it runs. With respect to disconnecting the vacuum to the distributor, I have the dual vacuum distributor, do I remove both lines, or just one? Thanks!

 

[72HCODE]

do you have the vacuum advance connected to ported vacuum or full manifold vacuum?

you want it in ported vacuum on the carburetor. ported is 0 HG" (no vac) at idle. This turns off the vacuum advance on the distributor at idle and you should get a much lower initial timing reading.

now your mechanical could have been messed with also. somebody could of swapped very soft springs on the mechanical or you might have a broken or missing spring.

to get a better reading, you would disconnect the vacuum advance, and plug the port on the carb or intake manifold. next lower engine RPMS until just above stall and take a reading. that should give you a baseline. if you are still seeing over 20 degrees of timing then either there is something very wrong with the distributor or you may not be reading the harmonic balancer timing marks correctly, or your balancer and timing marks may of shifted position. it is known to happen the rubber on the balancer shrinks and the cover with the timing marks then drifts and shifts around giving crazy readings.

you may need to replace your balancer and reset the engine to TDC on piston #1 to get a true reading, not a fun job.

 

[Don65Stang]

As mister4x4 pointed out in a round about way, timing will vary from one engine to another. Unless you have a brand new, factory spec engine, and running leaded gas, all factory setting are out the window. I have not used a timing light for 25 years when an old mechanic explained all the variables to me. He told me not all advances, carbs, heads, etc. are created equal and therefor require a personal setting especially as the engine ages and compression falls. He showed me to leave everything hooked up, bring engine to 2500 rpm, and set it just slightly retarded and that's the best it will get. This method has worked for me for years. just my 2 cents

All of the above posts are good info. Wendell's method is an excellent way to set the timing for anyone who doesn't have or doesn't want to use a timing light. It'll produce very good results.

If following the timing light advice mentioned in this thread (all accurate info), and building on what others have said you can also check your distributor's advance curve and your total advance. The total advance could be almost anything depending on the slot size of the plate inside the distributor. It's different on all of my Mach 1s due to 40 years where POs swapped out distributors along the way. Later model distributors have different mechanical advance limits. I dissected mine and welded the plate opening smaller so that it would allow exactly 20 degrees of rotation (mechanical advance). Before welding it up it allowed 36° of mechanical rotation! I have one distributor slot that allows 42° mechanical. Yikes!

Our cars like around 16° - 18° initial and 20° mechanical. My mechanical was 36°. 16° + 36° = 52° degrees total. WAY too much so I welded one side of the slot opening to limit it's travel to 10° which gives 36° total. Perfect. Pic below.

So...

Step 1. Determine your baseline timing. Let your engine warm up, disconnect and plug your vacuum line to the distributor, set your idle RPM to 700 or so then take a timing reading.

Step 2. Set your initial timing to 16°. You could also use a vacuum gauge to see what the highest engine vacuum is by rotating the distributor around and see what that timing reading is. I do this.

Step 3. Turn off your engine and try to restart. If it is hard to turn over rotate the distributor a little counter clockwise and retry. If it is hard to start at 16° might want to investigate your starting system condition. (Been there done that).

Step 4. Once you get the engine starting ok, ideally at 16° or so, rev it up to 3500 + rpm and take a total timing reading. Subtract the numbers to see what your mechanical advance is.

Step 5. With initial timing still at 16°, go for a drive and listen for light throttle pinging. If pinging occurs rotate the distributor a little counter clockwise. I just stop along the road and do this. Drive again - wash, rinse, repeat until there is no pinging. On the other hand if there is no pinging at 16° try rotating clockwise until you do get pinging then back off a bit to find the sweet spot. Drive home and check to see what you set the initial timing at during the test ride.

Step 6. Math. Subtract your test drive initial timing reading from 36° to determine what your mechanical advance needs to be. Compare that to what your actual mechanical advance your distributor currently has (see step 4).

Here's the fun step.

Step 7. Either find a 20° centrifugal advance curve requires a 10°/15° centrifugal advance cam assembly (#C5AZ-12210-B; having a cam plate stamped 10L-15L) or adjust your current distributor's mechanical advance slot size. Take the mechanical advance needed (step 6) and divide by 2 to get the slot size 10L = 20°, 13L = 26°, etc. This is the number of degrees the slot needs to rotate. Should be close to 20°. I'd just use 20° and be done with it.

In my case I altered the cam plate that was in my distributor by welding the slot opening smaller then filed to 0.410-inch which is a slot size size 10L that yields 20° of mechanical advance for 36° total advance...the perfect number. Actually I welded one side and I let my 8 year old weld the other side. I think his turned out better than my side but after grinding they both looked the same.

Step 8. Put the distributor back together. I used 1 light spring and 1 heavy spring to hold the cam plate. You can see the spring tabs in the pic above. New advance springs: either Mr. Gasket (kit #925D) or Crane Cams (kit #99607-1). The Mr. Gasket kit includes one pair of springs, the Crane Cams kit includes 3 pairs of springs AND an adjustable vacuum advance canister. The Crane Cams kit is obviously the way to go as it will allow you to adjust the vacuum advance as well as the mechanical advance. The mechanical advance curve should start advancing at 1200 rpm and advance 10° per 800 rpm to 10° per 1000 rpm. The curve starts at about 1200 engine rpm or so it should end at 2800 to 3200 engine rpm.

Step 9. Install distributor in engine and set to your initial timing determined in Step 5. Connect the vacuum advance to the carburetor’s ported vacuum connection. If the vacuum advance is adjustable it should be limited to about 10°. Drive and listen for any pinging. There should be no light throttle pinging. There may be some pinging while under load. If so then try slightly heaver spring(s) on the plate. It's an iterative process to dial it in perfectly.

Once dialed in take some readings and post your results. I'm currently still dialing mine in on the '71 4-speed car due to recently installed Duraspark II. So far it is running pretty darn good like it is but I want to get it laser beam accurate with the most advance possible without pinging. My next move is trying slightly lighter springs to bring on the advance a tad sooner.

 

[wwhite72]

If i recall correctly the duel vac provides a bit of retard when starting the engine and then switched to advance as soon as the engine is running? The top hose probably goes to ported and the one sticking out the front of the can goes to manifold correct? Probably would avoid any confusion by just taking the can out o the equation and pluggin em both. But i dont have a book in front of me.

 

[BrandonDindorf]

Mine with full load, in a case of the petal to the floor, not cruzing down the road loves 36 to 38 degrees timing. Its the best power band I found on the dyno. From gathered experience 351c's do like timing. With my vaccum advance down hill with the wind at my back, full machanical, the most ill see is probally 42 degrees. I wouldn't exceed that. Just an FYI

Help a newbie out!

I bought an andavce timing light so I could see where my car is set.

It's a 1973 351c with Edelbrock Performer intake and Thunder Series Carb. It runs pretty well, and idles great... right about 700RPMs in Drive at a stop. Right about 800-900 in park.

Anyway, I fired up the timing light, and it idle, my car is set close to 30 degree advance.

Does that make sense? Seems quite high to me, but then... I'm ignorant when it comes to tuning motors.

 

[Wolverine]

Unless you have a brand new, factory spec engine, and running leaded gas, all factory setting are out the window.

BINGO!!!

And, you would think your CAM Manufacturer would provide you with some timing advice. Piece of garbage CAM Mfr's.

Does your fancy gun have a 4/6/8 cyl switch? Make sure it is on 8 cyl

????

I think this is true of a dwell meter, but not of a timing light...

Once dialed in take some readings and post your results. I'm currently still dialing mine in on the '71 4-speed car due to recently installed Duraspark II. So far it is running pretty darn good like it is but I want to get it laser beam accurate with the most advance possible without pinging. My next move is trying slightly lighter springs to bring on the advance a tad sooner.

Your entire post is great info Don.

This group really needs to get two things:

1. A DISTRIBUTOR ADVANCE chart where you plug in your cam, your rear end(axle) ratio, your torque converter stall speed, rear auto tranny ratios, and it gives you some idea where your mechanical advance setting should be as well as your vacuum advance.

2.We also need a DISTRIBUTOR ADVANCE CALIBRATOR. You know, one of those machines where it turns the distributor and measures the advance. So when you put in those 20 degree advance springs you KNOW you are getting 20 degrees of advance.

Distributors...ugh.

Very few understand timing is more than rotating the distributor.

 

[Don65Stang]

Does your fancy gun have a 4/6/8 cyl switch? Make sure it is on 8 cyl

I think this is true of a dwell meter, but not of a timing light...

I think so too but my light does have a 2 cycle/ 4 cycle switch.

Once dialed in take some readings and post your results. I'm currently still dialing mine in on the '71 4-speed car due to recently installed Duraspark II. So far it is running pretty darn good like it is but I want to get it laser beam accurate with the most advance possible without pinging. My next move is trying slightly lighter springs to bring on the advance a tad sooner.

Your entire post is great info Don.

This group really needs to get two things:

1. A DISTRIBUTOR ADVANCE chart where you plug in your cam, your rear end(axle) ratio, your torque converter stall speed, rear auto tranny ratios, and it gives you some idea where your mechanical advance setting should be as well as your vacuum advance.

2.We also need a DISTRIBUTOR ADVANCE CALIBRATOR. You know, one of those machines where it turns the distributor and measures the advance. So when you put in those 20 degree advance springs you KNOW you are getting 20 degrees of advance.

Distributors...ugh.

Very few understand timing is more than rotating the distributor.

Thanks James.

One can measure the advance curve without a machine and with a programable timing light, $100ish, and pen & note paper.

On the paper make 2 columns. Col 1 is for RPM & Col 2 is for recording your timing at specific RPMs.

Pre-fill Column 1 with RPMs: 800, 1000, 1200, 1400,... up to 3600 RPMs.

Column 2 is where you or your helper writes down the timing readings as you raise the RPMs.

The fancy timing light should show RPMs, then hit the button to switch to timing to take the reading.

Pull and plug the vacuum line to the vacuum advance, make sure the engine is warmed up and have at it. It will take 5 minutes or less to do this with the majority of that time getting out and putting up the tools used and writing down column 1 info.

Easy peasy.

It you want to get fancy you can take your data and plot it on graph paper or in a spreadsheet to see what your advance curve looks like.

One thing I didn't mention in my earlier post with the steps is setting your points gap and dwell. But I'm feeling too lazy to mess with points and I'm sure a google search would turn up a "how to".

 

[Mister 4x4]

Points - schmoints. Duraspark, Baby!! ::thumb::

 

[wwhite72]

Try manifold vac rather than ported vac. may see smoother idle, and engine run slightly cooler.

 

[Don65Stang]

Try manifold vac rather than ported vac. may see smoother idle, and engine run slightly cooler.

My understanding is if a car is at optimal initial timing (around 16 - 18 degrees) instead of factory initial (6 degrees or so) then using manifold vac will advance the timing past optimal and take it to 26 degrees or so initial.

However, if running factory timing of 6 degrees of so and then use manifold vacuum to the vac advance then that'll get you to 16 degrees which would indeed make smoother idle and run cooler and put the engine at optimal initial timing. The problem is though that this is a faking the engine out because total timing would still be limited and therefore limit the performance of the engine.

All that from memory so someone correct if there is a logic leap of faith in there somewhere. Lol. Seriously, the whole port vs manifold vacuum is emissions related somehow and the details escape me at the moment so speak up if you have the missing ingredients.

 

[wwhite72]

http://www.bangshift.com/forum/showthread.php/33503-Ported-vs-manifold-vacuum-advance

i type way too slowly, i found this link has a good explanation.

 

[Go Time]

good post, great response, well done

 

[Joe Stang]

Ouch baby the GM gods has spoken ! I shudder to think of how many cars I swapped from manifold to ported vac. All of the carb manuals that come with a new carb tell you to hook it to ported.

 

[Don65Stang]

Courtesy of 72HCODE...

Well it's a little confusing and it has to do with emissions.

Pre1970 engines were set with a distributor curve that used full manifold vacuum all the time. After 1970 ported came into the picture.

Ported basically means at idle vacuum is turned off to the distributor. In the carburetor when the butterflies are closed to idle rpm a plate blocks the vacuum coming from the engine to the ported vacuum tube. Now the engine is still obviously making vacuum all the time but just the one little port to the vacuum advance is turned off. That forces the engine to run on mechanical only at idle which at idle is also turned off, or at least should be. Many guys install weak springs to get the mechanical all in before 2500 Rpms.

So ok why is the vacuum turned off at idle? Well it's cause of emissions. Hotter exhaust temp means less nox coming from the tail pipe to meet new emissions standards after 1970. Retarded timing means hotter exhaust temps. The idea being sitting in traffic with the car on and off idle less people would be exposed to exhaust fumes.

At any time off idle the vacuum advance will see full manifold vacuum.

Full manifold vacuum at idle will obviously advance timing and raise engine Rpms. So from a seat of the pants perspective if you just switched from ported to full manifold without any other changes then at idle the car will idle much higher advance timing more and off the line the car will feel faster.

Trouble is the distributor in our cars is designed to compensate for the ported vacuum so this may cause a car on lean edge to blow the engine when you gun it.

Too much advance too soon with too little fuel.

Early distributors have a different curve with different weights and timing plate angles. It's very slight but it does exist. On a factory original engine there was a huge range of tolerance so it almost didn't matter. In fact full manifold was used at idle in emergency over heat situations the dvcv duel vacuum control valve was an emergency overheat compensator used on AC cars and attached to the water pump housing, if an engine over heated past 205° the valve would open and at idle the vacuum advance would kick to full manifold vacuum, this raised engine Rpms which increased cooling fan Rpms and lowered exhaust manifold temps, engine would cool down then pop back to ported vacuum at idle.

The big deal is basically resetting timing to compensate for full manifold vacuum. So you switch to full manifold vac go for a normal spin and listen for ping. Ping happens back off 1-2 degrees till ping stops. Original cars didn't have adjustable vacuum advance but today you can also dial back the vacuum advance until ping stops and leave the mechanical alone. But you sort of limit the vacuum advance that way and its better to just back off the mechanical and retard timing.

With ported the engine is going to seem a touch lazy when you plant the pedal this is because the engine sort of hiccups when the ported comes off and full manifold kicks in, so for performance people don't like the hiccup and just go full manifold vacuum.

Every motor reacts differently to it and some motor builds cannot tolerate full manifold vac at idle. Usually it is best to experiment and see what works best for you. Some people get 1969 or 70 distributors or start looking for different mechanical plates to mess around with it.

Personally I didn't have any advantage on my engine in fact full manifold vac caused timing to advance too fast for my open chamber heads and it pinged so bad it was like marbles rolling around the mufflers.

That's something to think about as well. The open chamber heads really do not tolerate a lot of vacuum advance at the wrong time. The closed chamber 70-71 heads can go back to 69 spec with full manifold vacuum better and you feel like the engine is a making more power off the line.

There are ways to compensate for the hiccup with ported vac also.

People always argue about ported verse full manifold.

Higher exhaust temperatures might be the ticket on hooker headers since untreated they loose heat very fast and lower the combustion chamber temps too much sometimes. Or that might be a good thing because you can come up a heat range on plugs and make it up that way.

My personal experience besides the ping which I compensated for with more fuel really did nothing for me, and I went back to ported manifold and very heavy mechanical advance springs to hold back timing enough so I could jet down and save some fuel and not have the engine ping like crazy.

Really it's a hard thing to nail down which is why everyone has a opinion for or against there is truth that the older guys will tell you full manifold is the way to go. Where the mid 70s guys say no use ported and it has to do with the slight changes to the distributor curves when ported was introduced. The older guys always ran on full manifold and new emissions caused ported to exist so the first thing they did on new cars was tear the emissions crap off and go full manifold and the cars were pinging like crazy because they didn't realize ford compensated for the change in the distributors.

It's funny that many guys don't realized ported just means zero vac at idle that's it. They assume the vacuum signal is totally different at all throttle positions when its not. It's right up there with the myth a blown power valve causes rich idle. At idle only the transision slot is leaking fuel into the engine even if the power valve was blown the fuel circuit inside the carb is physically turned off with a plate making rich idle from a power Valve at idle impossible. Off idle then yes you have problems.

Hope this helps.

 

[Mister 4x4]

Insert "shiver then explode" smilie here.

 

[Don65Stang]

So anyone remember what the consensus is?

16º intital and 36º total timing?

manifold or ported vacuum?

I jest with my questions with the purpose of bumping the thread to the top of the pile with the hopes that new members may awaken their engines if they haven't adjusted their timing to other than factory specs.

 

[barnett468]

http://www.bangshift.com/forum/showthread.php/33503-Ported-vs-manifold-vacuum-advance

i type way too slowly, i found this link has a good explanation.

.

Unfortunately, that article has several inaccuracies and does not contain enough information, therefore it is misleading and it has caused myself and others countless hours explaining to others why it is a bad idea to simply plug a vacuum advance into manifold vacuum . . Also, due to the type of inaccuracies and omissions it has, it strongly suggests that the "author" was no more of an automotive engineer than Winnie The Pooh is and it suggests that the "author" simply made up a title for himself in an attempt to reinforce the validity of his claims.

Below are a few, simple, no brainer guidelines I personally use and occasionally suggest to others.

1. Never just shove a "high performance" distributor in and set the initial timing and think its good because in fact it may cause your car to run slower than the one you just took out.

2. Never bolt on a carb and think it will magically be perfectly jetted for your car because it won't be.

3. Never plug your vacuum advance into ported vacuum unless you test its effect in a scientific way AFTER all other tuning is done because in some cases, it will reduce performance.

Below in parentheses are some quotes from the article posted above with my replies below them.

WRONG

“Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing... ...throttle response…”

RIGHT

vacuum advance does not function under hard acceleration because the engine vacuum drops below to point at which the vacuum advance begins to work, therefore, it has no affect on acceleration...none, 0, zip.

xxxxx

WRONG

“After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark"...”

RIGHT

Just what century is he talking about because as you can see by the diagram below of a 1955 car from a factory gm service manual, the vacuum advance is clearly connected to ported vacuum and there were no emissions standards in 1955…none, 0 zip.

xxxxx

This is not only absolutely positively WRONG . . It is irresponsible and potentially hazardous to an engine.

“For peak engine performance, drivability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.”

RIGHT

Immediately above around 1/8th throttle, the ported vacuum switches to full manifold vacuum and therefore operates the vacuum advance unit exactly the same way connecting the distributor to manifold vacuum does. The ONLY difference between ported and manifold vacuum is that at idle and deceleration, the manifold vacuum advances the timing.

When properly setup and the vehicle is allowed to coast a little before the brake is applied, using manifold vacuum can also increase mileage.

Advancing your initial timing to high numbers will have little affect on your mileage at idle.

.

 

[Mister 4x4]

OK - can you clean that up a bit? I have no idea which thoughts you're trying to get across as "Right," and which are "Wrong." Maybe put the words "Right" and "Wrong" closer to the thoughts they address - either before or after. Example: RIGHT - (sentence). Or (sentence) - WRONG. As long as they're somehow connected, it'll make more sense to we who aren't as well-versed in the intricacies of timing.

Sorry - but that's a LOT of information that's either right or wrong. Can you also explain how you came to these conclusions?

 

[barnett468]

OK - can you clean that up a bit? I have no idea which thoughts you're trying to get across as "Right," and which are "Wrong." Maybe put the words "Right" and "Wrong" closer to the thoughts they address - either before or after. Example: RIGHT - (sentence). Or (sentence) - WRONG. As long as they're somehow connected, it'll make more sense to we who aren't as well-versed in the intricacies of timing.

Sorry - but that's a LOT of information that's either right or wrong. Can you also explain how you came to these conclusions?

ok, my apologies for the confusion . . im not exactly what your question is and i will be happy to answer it in more detail if you can make it more clear for me but i can at least say this . . the word "wrong" is immediately above the quote from the article that was posted and it means that the quote is factually wrong . . it is not an opinion . . the word "right" is above the statement that is more correct and again is not an opinion.

one of the single biggest problems with that article is that it basically implies that if your car distributor is currently connected to ported vac, it will [perform far better if you connect it to manifold vac which couldn't be farther from the truth.

this post from this thread does not provide any technical info at all, however, imo, in general, it is better than the article posted here because it simply suggests that one "try" manifold vac vs ported vac, it does not demonstrably state that it is better.

Try manifold vac rather than ported vac. may see smoother idle, and engine run slightly cooler.

cliff ruggles whom is a quadrajet king and has a high perf street engine has his distributor vacuum connected to ported vac.

.