vacuum retard
06-04-2005, 01:25 AM
#1
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vacuum retard
Well i've been working down my list of things to fix, and slowly but surely my car is becoming... normal, in a super hot 1968 mustang way. Anyways, I was wondering if, anyone could explain to me the function and neseccity of a vacuum retard. One of my ex's was a mechanic and mentioned something about my car missing a vacuum retard system. If i remember correctly, we had a shop test it and I guess not only is one of the line/hoses missing but whatever it is that makes the vacuum retard work isn't working either. I was trying to look it up.. but couldn't really find much. A baisic explanation or a website with simple info would be greatly apreciated. Thanks.
06-04-2005, 01:39 AM
#2
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RE: vacuum retard
http://www.mustangmonthly.com/howto/26823/
This is Part II. Gives a lot of insight on Mustang Tuning
This is Part II. Gives a lot of insight on Mustang Tuning
06-04-2005, 01:46 AM
#3
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RE: vacuum retard
ORIGINAL: Markstang1969
http://www.mustangmonthly.com/howto/26823/
This is Part II. Gives a lot of insight on Mustang Tuning
http://www.mustangmonthly.com/howto/26823/
This is Part II. Gives a lot of insight on Mustang Tuning
06-04-2005, 01:57 AM
#4
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RE: vacuum retard
Basically, AT higher RPMs the spark needs to fire EARLIER to create combustion. The Vacuum advance speeds up the timing as rpms are raised to accomplish this:
http://mustangandfords.com/techartic...nition_basics/
In time, automotive engineers developed spark-advance mechanisms that advanced the spark automatically as engine rpm increased. It was a simple flyweight system that advanced the spark as engine revs (and distributor speed) increased. The vacuum advance came along later to compliment the mechanical advance. The combination of the two types of advance units offered motorists a seamless transition from idle to power mode. Leaning on the throttle worked the vacuum advance (breaker plate) to get the vehicle moving. The mechanical (centrifugal) advance advanced the rotor indexing at higher revs. Think of it this way--the vacuum advance advances the breaker plate positioning when we're under initial acceleration. As vehicle speed and engine revs roll into higher rpm ranges, the centrifugal flyweights swing outward and advance the rotor positioning for an earlier spark.
We want an earlier spark at high revs because fuel doesn't ignite the way we think it does inside an engine. When we think of the four-stroke cycle, we think intake, compression/ignition, power, exhaust, but it's more complicated than that. Fuel and air do not "explode" in the combustion chamber like we were taught in Auto Shop 101. Fuel ignites in a quick-fire like it does in your water heater or furnace with a woof. If you've ever been startled by a sudden furnace or water heater light-up when you were lighting the pilot light and felt the blast of heat and air, you experienced the energy of thermal expansion. This is the same kind of energy that powers your engine.
As the piston rises in the cylinder on compression/ignition stroke, the fuel does not ignite at top-dead-center (TDC). The fuel needs to be ignited around 6 to 12 degrees before top-dead-center (BTDC) because fuel does not ignite instantly. It lights more slowly than we think. We have to allow the piston time to reach TDC before full combustion is underway. When we increase rpm, we need to allow the richer fuel charge more time to ignite. This is why we "advance" the spark and make it occur earlier during the compression/ignition stroke. Most of the time, that is 34-36 degrees BTDC. Pushing the spark timing any earlier can cause detonation and engine damage.
http://mustangandfords.com/techartic...nition_basics/
In time, automotive engineers developed spark-advance mechanisms that advanced the spark automatically as engine rpm increased. It was a simple flyweight system that advanced the spark as engine revs (and distributor speed) increased. The vacuum advance came along later to compliment the mechanical advance. The combination of the two types of advance units offered motorists a seamless transition from idle to power mode. Leaning on the throttle worked the vacuum advance (breaker plate) to get the vehicle moving. The mechanical (centrifugal) advance advanced the rotor indexing at higher revs. Think of it this way--the vacuum advance advances the breaker plate positioning when we're under initial acceleration. As vehicle speed and engine revs roll into higher rpm ranges, the centrifugal flyweights swing outward and advance the rotor positioning for an earlier spark.
We want an earlier spark at high revs because fuel doesn't ignite the way we think it does inside an engine. When we think of the four-stroke cycle, we think intake, compression/ignition, power, exhaust, but it's more complicated than that. Fuel and air do not "explode" in the combustion chamber like we were taught in Auto Shop 101. Fuel ignites in a quick-fire like it does in your water heater or furnace with a woof. If you've ever been startled by a sudden furnace or water heater light-up when you were lighting the pilot light and felt the blast of heat and air, you experienced the energy of thermal expansion. This is the same kind of energy that powers your engine.
As the piston rises in the cylinder on compression/ignition stroke, the fuel does not ignite at top-dead-center (TDC). The fuel needs to be ignited around 6 to 12 degrees before top-dead-center (BTDC) because fuel does not ignite instantly. It lights more slowly than we think. We have to allow the piston time to reach TDC before full combustion is underway. When we increase rpm, we need to allow the richer fuel charge more time to ignite. This is why we "advance" the spark and make it occur earlier during the compression/ignition stroke. Most of the time, that is 34-36 degrees BTDC. Pushing the spark timing any earlier can cause detonation and engine damage.
06-04-2005, 06:27 AM
#5
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RE: vacuum retard
Yeah, Mark probably got your head spinning with too much information. Let's try to simplify it for you. Take a look at this distributor. You will see a vacuum advance mechanism at the heel of his hand. If you have that on your distributor, then simply run a vacuum hose to a vacuum port on your intake manifold. As the vacuum increases with higher RPM, the mechanism will turn your distributor slightly to change the timing. It's just that simple. If you don't have a distributor with the vacuum advance mechanism, get one. Most likely you do though. http://sporttruck.com/techarticles/p...mage_small.jpg
Let's try to simplify it for you. Take a look at this distributor. You will see a vacuum advance mechanism at the heel of his hand. If you have that on your distributor, then simply run a vacuum hose to a vacuum port on your intake manifold. As the vacuum increases with higher RPM, the mechanism will turn your distributor slightly to change the timing. It's just that simple. If you don't have a distributor with the vacuum advance mechanism, get one. Most likely you do though. http://sporttruck.com/techarticles/p...mage_small.jpg
06-04-2005, 01:09 PM
#7
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RE: vacuum retard
Great explanations of what adjustable timing is for guys!
The vacuum retard was in direct result of us looking at oxides of Nitrogen (NOx), which are caused by high combustion chamber temperatures. It was our first real attempt to find a way to cool the combustion chamber thereby reducing NOx. It has almost the direct oposite effect on efficiency. What we are trying to do is not fully burn the mixture thereby allowing raw gasses to carry away the excess heat.
Engineers have since learned how to affect NOx by shaping of the cylinder head, placement of the initial spark, and how gas charges into the cylinder, making the vacuum retard an unneccesary device.
If you want a more indepth explanation look up NOx (not NOS) you should be able to "google" some good stuff.
In means of performance and efficiency it is not as good as a well tuned centrifugal/vacuum advance distributor that is properly "curved".
HTH,
The vacuum retard was in direct result of us looking at oxides of Nitrogen (NOx), which are caused by high combustion chamber temperatures. It was our first real attempt to find a way to cool the combustion chamber thereby reducing NOx. It has almost the direct oposite effect on efficiency. What we are trying to do is not fully burn the mixture thereby allowing raw gasses to carry away the excess heat.
Engineers have since learned how to affect NOx by shaping of the cylinder head, placement of the initial spark, and how gas charges into the cylinder, making the vacuum retard an unneccesary device.
If you want a more indepth explanation look up NOx (not NOS) you should be able to "google" some good stuff.
In means of performance and efficiency it is not as good as a well tuned centrifugal/vacuum advance distributor that is properly "curved".
HTH,
06-04-2005, 03:59 PM
#9
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RE: vacuum retard
Exactly,
This had nothing at all to do with performance or racing. It was strictly done to "help" emissions on street cars.
That's what is so stupid about the Vacuum retarder deal, and you can blame the whole thing on Southern California. Back in the 60's the smog was so bad down there that they basically forced the auto manufactures into this whole train of thought.
It was the antithesis of performance.
Not sure if they made you do this in Texas, but we actually had to add NOx devices to retrofit late 60's cars. It basically shut down the vacuum advance at a certain temperature. I refused to put them on.
Don't get me wrong, I fully appreciate where we have come, and L.A. is a shining example of what can be done. You can actually breath now while your stuck in traffic (for hours at a time). The sore spot for me is that we suffered through years of really crappy running cars because of it.
This had nothing at all to do with performance or racing. It was strictly done to "help" emissions on street cars.
That's what is so stupid about the Vacuum retarder deal, and you can blame the whole thing on Southern California. Back in the 60's the smog was so bad down there that they basically forced the auto manufactures into this whole train of thought.
It was the antithesis of performance.
Not sure if they made you do this in Texas, but we actually had to add NOx devices to retrofit late 60's cars. It basically shut down the vacuum advance at a certain temperature. I refused to put them on.
Don't get me wrong, I fully appreciate where we have come, and L.A. is a shining example of what can be done. You can actually breath now while your stuck in traffic (for hours at a time). The sore spot for me is that we suffered through years of really crappy running cars because of it.
06-04-2005, 04:22 PM
#10
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RE: vacuum retard
SO my vacuum retard is not needed? And should I check to see if my vacuum advance works?
I guess I'm just conufsed because my question was about vacuum retard and until Scott H. here, you all talked about vacuum advance.
Lemme see if I've got this on a baisic level.... Vacuum advance adjusts spark timing at higer RPMs, while vacuum retard sets the spark timing back to normal for emissions purposes?
I guess I'm just conufsed because my question was about vacuum retard and until Scott H. here, you all talked about vacuum advance.
Lemme see if I've got this on a baisic level.... Vacuum advance adjusts spark timing at higer RPMs, while vacuum retard sets the spark timing back to normal for emissions purposes?