Johnny Dart
Well-Known Member
At this point, is there really a best way ? :scratch:
Starting to wonder if we're on Candid Camera.
questions on timing an engine
- Thread starter pjc360
- Start date
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At this point, is there really a best way ? :scratch:
Starting to wonder if we're on Candid Camera.
I was curious. This Q&A states that the vacuum advance isn't considered for total. It comes in and goes with throttle/vacuum.
Q: What's the difference between mechanical and vacuum advance?
A: Mechanical advance is the centrifugal weight and spring assembly located underneath the rotor that provides the largest part of the
timing curve. The vacuum advance canister, located on the side of the distributor, provides additional timing only when the engine is pulling
vacuum. The mechanical advance along with the initial advance (base timing set at idle) is what gives you total timing. An example of total
timing would be 12° initial plus 24° of mechanical which equals to 36° total. Vacuum advance is not figured into total timing because it will
only function when the engine is not under a load. Example: If your vehicle is cruising on a flat stretch of road or going downhill, vacuum
advance will come in and add as much as 15° to the total timing for increased fuel mileage and cleaner spark plugs. It is not uncommon to
see as much as 50° - 52° of timing with vacuum advance. But don't be alarmed by this being too much timing as the vacuum advance will
decrease once you accelerate and put the engine under a load. Under hard acceleration the timing will go back to the original total with no
vacuum advance.
Q: What's the difference between mechanical and vacuum advance?
A: Mechanical advance is the centrifugal weight and spring assembly located underneath the rotor that provides the largest part of the
timing curve. The vacuum advance canister, located on the side of the distributor, provides additional timing only when the engine is pulling
vacuum. The mechanical advance along with the initial advance (base timing set at idle) is what gives you total timing. An example of total
timing would be 12° initial plus 24° of mechanical which equals to 36° total. Vacuum advance is not figured into total timing because it will
only function when the engine is not under a load. Example: If your vehicle is cruising on a flat stretch of road or going downhill, vacuum
advance will come in and add as much as 15° to the total timing for increased fuel mileage and cleaner spark plugs. It is not uncommon to
see as much as 50° - 52° of timing with vacuum advance. But don't be alarmed by this being too much timing as the vacuum advance will
decrease once you accelerate and put the engine under a load. Under hard acceleration the timing will go back to the original total with no
vacuum advance.
Yep, I know what you mean.
Problem with total timing method, you're at the mercy of whatever the distributor has in it for advance. ex. engine wants 34 total, distributor has 28* in it... 6* initial... no thanks. I don't even run stock engines with less than 10* initial.
...
How many of you guys run vacuum advance? If you do which port do you connect the hose to? I tried both ways and the constant vacuum port makes it run much better. tmm
When it was dynoed the guy didnt mess with the timing he left it where i have it at. And i get the point now and to better answer 67dart273 when i set the initial timing at 10 degrees then rev up to 3000 rpm and pull it back to 35 degrees and let go of the throttle and check the initial again it reads 8 degrees on my timing light, so does that mean i have a long curve or fast curve?
Mad Dart
Nothing to see Here!
Long curve, there is 27* of mechanical advance built into the Dizzy. Time for a re curve. You want 16* initial and about 18* of mechanical advance built into your Dizzy. 34* or so all in with the vac line capped off during your timing light readings.
You need to do some reading on the subject of engine timing. As it has been said previously there are three components that dictate the timing curve an engine has. In this example I am talking about a street driven engine, not a track only race engine.
First component is initial or base timing. This is the degrees of advance an engine sees at idle rpm generally 900 rpm or less. It is constant, does not change with rpm or vacuum.
Second component is mechanical or centrifugal advance. This advance is added based on an increase of engine rpm over idle to the base setting up to a predetermined value. Most street driven engines like around 30 degrees of advance give or take of base plus mechanical. Base timing added to mechanical advance timing = the sweet spot where engine can develop maximum power without any pinging or spark knock.
Mechanical advance is controlled by the length of two slots located inside the distributor that allow, or limit a pair of weights to travel based on engine rpm and keeper spring tension out from distributor’s center shaft not unlike a governor would function. Previously someone listed the length of these slots needed to produce a given amount of advance. The shorter the slot is the less mechanical timing that can be added to the mix. To read mechanical advance with timing light, vacuum advance vacuum hose must be disconnected from carburetor, and its tap caped off to prevent a vacuum leak condition.
Third component of advance is rather ingenious, the vacuum advance. Previously I said an engine can only be advance to around 30 degrees to keep it from pinging under hard acceleration, or load. However that same engine under light load, such as steady cruise on level ground, can tolerate an additional 20 degrees or so of timing to return better fuel economy. The ingenious part of this device is based on how or when the engine develops or loses vacuum under different load conditions.
You know that when engine is under wide open throttle (WOT) vacuum drops to near zero, and when coasting down a hill with little load, it will develop maximum vacuum perhaps into the low 20’s inches Hg. The vacuum advance diaphragm reads these different vacuum conditions and adjusts timing automatically. As vacuum increases timing is added in up to around 20 additional degrees over the base and mechanical advance. As engine comes under load, that additional 20 degrees of advance can be reduced to zero leaving just the base and mechanical component.
Vacuum advance will not activate at idle if connected to ported vacuum tap on carburetor. This tap is located on atmospheric pressure side of throttle plates, or in other words, above the throttle plates, and won’t see any engine vacuum at idle. As throttle plates are opened this tap is exposed to engine vacuum, at which time the vacuum advance can is activated.
To sum up; base timing + mechanical timing + vacuum advance = total timing.
Depending on rpm and load conditions, timing can vary between base setting at idle to somewhere near 50 degrees of advance.
The tricky part to this timing biz is to determine what your engine likes for timing throughout its rpm range under varying load conditions. Not all engines have the same timing requirements, and each vehicle has different weight and aerodynamics that contribute to the load an engine sees. In other words a light car will have different timing requirements than a heavy truck.
Generally 10 to 16 degrees of base advance a good starting point.
Full load condition, most engines like 28 to 35 degrees of timing, just how fast the timing needs to be dialed in will depend on a particular engine’s build and converter stall speed. Perhaps someone with a 360 build similar to yours could chime in with their settings for a rough starting point.
Vacuum advance will also have to be dialed in. The diaphragm can be adjusted by an Allen wrench when to react to a given vacuum level and propensity of a given engine to ping under light load.
Curving, or developing an advance curve for a particular engine without a machine designed for such projects, is a trial and error endeavor. Here is an article on re-curving a distributor with nice photos showing slots, and weights.
http://www.slantsix.org/forum/viewtopic.php?t=46266
Here is a list of vacuum cans, not all of them are V8 cans, but one can see that there is a selection based on vacuum level and amount of advance available.
http://www.slantsix.org/forum/viewtopic.php?t=13198
Here is more reading on re-curving showing how I worked through my first attempt on a high performance slant six. A straight six has different timing requirements than a V8, but the curving process is the same. Recommended reading if you are having problems sleeping… LOL
http://www.slantsix.org/forum/viewtopic.php?t=38471
First component is initial or base timing. This is the degrees of advance an engine sees at idle rpm generally 900 rpm or less. It is constant, does not change with rpm or vacuum.
Second component is mechanical or centrifugal advance. This advance is added based on an increase of engine rpm over idle to the base setting up to a predetermined value. Most street driven engines like around 30 degrees of advance give or take of base plus mechanical. Base timing added to mechanical advance timing = the sweet spot where engine can develop maximum power without any pinging or spark knock.
Mechanical advance is controlled by the length of two slots located inside the distributor that allow, or limit a pair of weights to travel based on engine rpm and keeper spring tension out from distributor’s center shaft not unlike a governor would function. Previously someone listed the length of these slots needed to produce a given amount of advance. The shorter the slot is the less mechanical timing that can be added to the mix. To read mechanical advance with timing light, vacuum advance vacuum hose must be disconnected from carburetor, and its tap caped off to prevent a vacuum leak condition.
Third component of advance is rather ingenious, the vacuum advance. Previously I said an engine can only be advance to around 30 degrees to keep it from pinging under hard acceleration, or load. However that same engine under light load, such as steady cruise on level ground, can tolerate an additional 20 degrees or so of timing to return better fuel economy. The ingenious part of this device is based on how or when the engine develops or loses vacuum under different load conditions.
You know that when engine is under wide open throttle (WOT) vacuum drops to near zero, and when coasting down a hill with little load, it will develop maximum vacuum perhaps into the low 20’s inches Hg. The vacuum advance diaphragm reads these different vacuum conditions and adjusts timing automatically. As vacuum increases timing is added in up to around 20 additional degrees over the base and mechanical advance. As engine comes under load, that additional 20 degrees of advance can be reduced to zero leaving just the base and mechanical component.
Vacuum advance will not activate at idle if connected to ported vacuum tap on carburetor. This tap is located on atmospheric pressure side of throttle plates, or in other words, above the throttle plates, and won’t see any engine vacuum at idle. As throttle plates are opened this tap is exposed to engine vacuum, at which time the vacuum advance can is activated.
To sum up; base timing + mechanical timing + vacuum advance = total timing.
Depending on rpm and load conditions, timing can vary between base setting at idle to somewhere near 50 degrees of advance.
The tricky part to this timing biz is to determine what your engine likes for timing throughout its rpm range under varying load conditions. Not all engines have the same timing requirements, and each vehicle has different weight and aerodynamics that contribute to the load an engine sees. In other words a light car will have different timing requirements than a heavy truck.
Generally 10 to 16 degrees of base advance a good starting point.
Full load condition, most engines like 28 to 35 degrees of timing, just how fast the timing needs to be dialed in will depend on a particular engine’s build and converter stall speed. Perhaps someone with a 360 build similar to yours could chime in with their settings for a rough starting point.
Vacuum advance will also have to be dialed in. The diaphragm can be adjusted by an Allen wrench when to react to a given vacuum level and propensity of a given engine to ping under light load.
Curving, or developing an advance curve for a particular engine without a machine designed for such projects, is a trial and error endeavor. Here is an article on re-curving a distributor with nice photos showing slots, and weights.
http://www.slantsix.org/forum/viewtopic.php?t=46266
Here is a list of vacuum cans, not all of them are V8 cans, but one can see that there is a selection based on vacuum level and amount of advance available.
http://www.slantsix.org/forum/viewtopic.php?t=13198
Here is more reading on re-curving showing how I worked through my first attempt on a high performance slant six. A straight six has different timing requirements than a V8, but the curving process is the same. Recommended reading if you are having problems sleeping… LOL
http://www.slantsix.org/forum/viewtopic.php?t=38471
What kind of high performance distributer should i be lookin into getting? has anyone here ran the dui ignition the tri pod distributers? or should i get a msd or mallory distributer and run the chrysler electronic ignition to the aftermarket distributer? this is for future thought by the way.
Mad Dart
Nothing to see Here!
Run what you brung. Just get some new springs and recurve it.
If it even needs to be re-curved? somone said i ha a long curve because when i set the initial timing at 10 degrees and then rev up to 3000 rpm and set it at 35 and then check initial again it is at 8 degrees initial. I had played around with the timing quite a bit today and what runs best and sounds best is 8 degrees initial timing, keep in mind the engine is behind a 4 speed A-518 auto tranny \, i have been told the initial timing is normally a tad bit lower in an auto vs a manual? But this engine seems at its best with the timing set at 35 degrees at 3000 rpm and that brings the initial timing to 8 degrees and that seems to be its sweet spot. It has the stock cam shaft that came with the engine and from what i have been told its a relatively stock cam. It's got hedman headers dual exhaust with 2 inch exhaust pipe and an h pipe with a dual plane edelbrock rpm air gap inta and a 600cfm manual choke edelbrock carburetor with the mopar electronic ignition with vaccume advance distributer. It's not nything real wild but it does have some good bolt on parts on it. Like i said when i had it dynoed it was set at 8 degrees initial timing 35 degrees at 3000 rpm and it was putting out 319 horse power and 424 ft lbs of torque not exactly a high horse power engine but i'm happy with having more torque because this engine is in a 91 short box dodge four wheel drive so he torque is nice. I will buy a spring kit and get into the timing soon, but where it is at sounds best and runs best to me, i did several runs down my street with the initial at 5,8,10 and 12 and at 8 is its sweet spot. I have been told that the magnum heads do not require as much timing dont know how true that is?
By the way I appriciate all your guy's info i will purchase a spring kit and learn how to re-curve the distributer and i will get into all of this very soon and i'm sure i will have more questions for guys regarding it.
Johnny Dart
Well-Known Member
A guick or quicker advance is prefered in a lighter car.
Had no idea you are working on a heavier truck. With a heavier vehicle,you want your advance to come in a little slower. As far as
re-curving your distributor, you might be just fine right where your at.
Had no idea you are working on a heavier truck. With a heavier vehicle,you want your advance to come in a little slower. As far as
re-curving your distributor, you might be just fine right where your at.
Last time for me...
Rev the engine up UNTIL IT STOPS ADVANCING! Note the difference between that number and the number of your initial.
You mentioned information earlier that displayed it had more advance in it than what you observed at 3K. If it's done advancing at 3K, great, if not, you'll have issues.
Rev the engine up UNTIL IT STOPS ADVANCING! Note the difference between that number and the number of your initial.
You mentioned information earlier that displayed it had more advance in it than what you observed at 3K. If it's done advancing at 3K, great, if not, you'll have issues.
Slowly raise the engine rpm until the timing mark quits advancing on the balancer.
ok bear with me guys i think i am understanding this a little better, i just read something on timing small block mopars and the magnum particular the 360 magnum as i have it said the magnum engines run best at 32 to 35 degrees total timing. So when i set my initial timing at 10 degrees then rev up to 3000 rpm and set it at 35 degrees and back off and check my initial it is back down to 8 degrees initial, so 8 degrees initial plus 35 degrees mechanical is 43 degrees, isnt that a little much? i thought i had read somehwere where a guy was running 40 to 42 degrees of total timing on a 360 magnum but cant remember where i read it. So in order for me to get 35 degrees total i will have to rev up to 3000 rpm and pull it back to 30 degrees mechanical and check my initial and that should bring my initial to around 5 or 6 degrees, that would give me a total timing of 35 or 36 degrees correct? and the whole while having the vaccume advance plugged off.
And since i have been driving around with my total timing at 42 to 43 degrees i have not heard any engine ping at all, but i do run 91 octane pump gas could that be why i am not hearing any pinging at that high of timing? and since i am not hearing any pinging should i just leave it right where its at? because i have had some guys tell me that they advance there timing untill they hear pinging and then they back it off a couple degrees and leave it that way.
camd64
Remember Landy
[ame="http://www.youtube.com/watch?v=FZxsp7S7ZhQ&feature=related"]How to Set the Ignition Timing on Your Car's Engine - YouTube[/ame]
i'm thinking that since i'm running premium fuel having 42 degrees total timing is about right on 91 octane fuel. if its not i can set mechanical to 30 wich will lnd my initial to 5 or 6 degrees wich would give me a total of 35 or 36 degrees total timing and i could go back down to 87 octane but the book that came with this engine reccomends running 91 octane because of the compression ratio wich is 9 to 5 to 1 i believe?
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