Vacuum Advance
01-21-2009, 10:55 PM
#41
Race Director
That's exactly my thought too. Do they put such inferior parts in their rebuilds that they need to be detuned. Seem like they are afraid of something. I'd just stay with one of the genuine GM engines and combinations that are offerfed.
01-22-2009, 06:36 AM
#42
Racer
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St. Jude Donor '03 & '05
Buns,
Go for it.
I'd call them but I don't know all the technical aspects to be able to debate there point.
That's why I brought up the thread to begin with. It's all new stuff for me and I'm trying to process everyones comments.
Mark
Go for it.
I'd call them but I don't know all the technical aspects to be able to debate there point.
That's why I brought up the thread to begin with. It's all new stuff for me and I'm trying to process everyones comments.
Mark
01-22-2009, 07:41 AM
#43
Racer
this must be due to the fact that more folks do not know how to time their engines with today's un leaded fuels. to un properly time an engine AND also use a vc, could be un kind to the mill. i have written many posts on this timing subject on this forum until im blue in the face, i don't like being blue mainly because it is a ford color, so ill just say this....this vc cannister argument falls into two distinct and stubborn camps,those that swear by it and those who dont...im in the latter camp....usually the folks who like vc, haven't taken the time to set up strictly mec. advance the proper way....there are sooo many pieces written pro vc and many are laughable....so im not going to open this can of worms any more.......it's all about today's fuels......
A clearing in the clouds. Someone finally said the magic words.
Todays fuels.
I too have preached over this and the need for proper ignition curve (including using the vac can or you will be missing 1/2 the fun, unless you launch from stop signs at 2500 and up) fuel load, whether carb or injected. Its a whole different game today and adjustments need to be made
Here in Conn, as a GENERAL rule I am forced #1 to richen up the fuel load across the board upwards of 15-20%, #2 I ALWAYS go to Delco's Rapid fire plug, I am then able to dail back in all the advance that was designed in to be used in a particular engine package and beyond.
Keep in mind thats a general rule, and my engines never suffer from any type of pre-ignition. We will not even bring up compression ratio affecting that as that is a complete variable dependent upon camshaft selection
Any way, use the vacum advance and learn how to use it, if it came with one on it then both curves are designed to be used together,tune your entire package, figure a starting point with the vac advance unplugged at about 9 degrees BTDC and keep it below 38 degree's all in keep and you will be happy. Be certain you are using ported vacum source to hook up the advance
Have fun and keep us informed on progress!
Bill
01-22-2009, 07:46 AM
#44
Racer
Nonsense. Every engine, regardless of its performance capability, has a cylinder density/residual EGR/burnrate curve. Running the same absolute timing advance at light loads as heavy loads causes the combustion thermal efficiency to decrease significantly, producing a crappy idle, overheating, hotter exhaust valves, and poorer fuel economy. Running without a vacuum advance went out in the sixties (along with roadhugging weight).
I run a vacuum advance unit on my street/track (road course, not short quarter mile jaunts) 427, and the extra advance cleans up the idle quality, reduces dieseling at shutdown, and improves the gas mileage/throttle response on these reasonably unsophisticated cars.
I run a vacuum advance unit on my street/track (road course, not short quarter mile jaunts) 427, and the extra advance cleans up the idle quality, reduces dieseling at shutdown, and improves the gas mileage/throttle response on these reasonably unsophisticated cars.
01-22-2009, 08:00 AM
#45
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Mike, your explanation seems to make sense, if all of the mixture is burned. My rich/lean remark was based on my understanding that less than optimum advance results in incomplete burning. If that were the case then incomplete burn is effectively a "rich mixture". But, I learn a little more about this stuff every day. Thanks for the feedback. In any case, I still agree with you on the need for vacuum advance.
Harry
Harry
Thanks for responding back about my puzzlement regarding your rich/lean comment. This shouldn't be a real possibility. If the carburetor is doing its job (atomizing/mixing the fuel with the incoming air) the air/fuel in the cylinder should be a reasonably homogeneous mixture. Regardless of when the mixture is lit off, there will be both fuel and air being burned (chemically combined) in the ratio needed to continue combustion. If the timing is correct, everything gets burned in the cylinder prior to the exhaust valve opening. (Maximum efficiency.) If the timing is retarded, the combustion will still burn at a somewhat similar rate (although the difference in piston position will cause secondary,lower pressure issues most probably reducing the burn rate), and there is increased possibility that the combustion will not be complete before the exhaust valve opens. The combustion would then just complete itself while it is passing out the exhaust port and into the header pipes. The last scenario is if there is some sort of combustion anomaly that would snuff out the flame front. Stopping the combustion would result in both (chemically uncombined) air and fuel being pumped out of the cylinder. It's not possible for just the fuel or air to burn by itself. Chemically, it requires both components in a defined weight ratio.
01-22-2009, 09:01 AM
#46
Le Mans Master
I was deliberately avoiding commenting on this thread since I'm sick of the vacuum / no vacuum debate but I have to disagree on that one statement.
Ported vacuum was used ONLY because of emissions reasons. For best performance, throttle response, fuel economy, idle characteristics, and operating temps full manifold vacuum is the preferred method.
Ported vacuum was only used in conjunction with severely retarded initial timing settings on the later cars (some later C2's and early to mid C3's) and much leaner fuel mixtures. The goal was to increase operating temps, especially at idle, to reduce HC output. It had a definate negative impact on performance and most other operating parameters of the motor though. In fact, once they added Cats to the exhaust system to reduce the emissions output they found they were able to go back to using full manifold vacuum which they did because it's a much better set-up.
Ported vacuum was used ONLY because of emissions reasons. For best performance, throttle response, fuel economy, idle characteristics, and operating temps full manifold vacuum is the preferred method.
Ported vacuum was only used in conjunction with severely retarded initial timing settings on the later cars (some later C2's and early to mid C3's) and much leaner fuel mixtures. The goal was to increase operating temps, especially at idle, to reduce HC output. It had a definate negative impact on performance and most other operating parameters of the motor though. In fact, once they added Cats to the exhaust system to reduce the emissions output they found they were able to go back to using full manifold vacuum which they did because it's a much better set-up.
01-22-2009, 09:15 AM
#47
Racer
I was deliberately avoiding commenting on this thread since I'm sick of the vacuum / no vacuum debate but I have to disagree on that one statement.
Ported vacuum was used ONLY because of emissions reasons. For best performance, throttle response, fuel economy, idle characteristics, and operating temps full manifold vacuum is the preferred method.
Ported vacuum was only used in conjunction with severely retarded initial timing settings on the later cars (some later C2's and early to mid C3's) and much leaner fuel mixtures. The goal was to increase operating temps, especially at idle, to reduce HC output. It had a definate negative impact on performance and most other operating parameters of the motor though. In fact, once they added Cats to the exhaust system to reduce the emissions output they found they were able to go back to using full manifold vacuum which they did because it's a much better set-up.
Ported vacuum was used ONLY because of emissions reasons. For best performance, throttle response, fuel economy, idle characteristics, and operating temps full manifold vacuum is the preferred method.
Ported vacuum was only used in conjunction with severely retarded initial timing settings on the later cars (some later C2's and early to mid C3's) and much leaner fuel mixtures. The goal was to increase operating temps, especially at idle, to reduce HC output. It had a definate negative impact on performance and most other operating parameters of the motor though. In fact, once they added Cats to the exhaust system to reduce the emissions output they found they were able to go back to using full manifold vacuum which they did because it's a much better set-up.
Here maybe I will learn sumptin' and am more than willing to digress.
But I think you have it backward or our (my) terminology is flawed, I have a 65 350 hp car with the 2818, I see you have a 365, clearly the vacum advance is hooked up to ported vacum source on the metering plate, as is most if not all of the early quadrajets pre emmissions.
I start seeing full manifold vacum use in 66 on the holleys, 3367's etc.
The way I am seeing it, ported vac source equates to more advance in as the throttle plates open, manifold source retards advance as throttle plates open.
What am I missing? Thanks for responding even though it appears an old wound!
Bill
01-22-2009, 12:04 PM
#48
Le Mans Master
Barry,
Here maybe I will learn sumptin' and am more than willing to digress.
But I think you have it backward or our (my) terminology is flawed, I have a 65 350 hp car with the 2818, I see you have a 365, clearly the vacum advance is hooked up to ported vacum source on the metering plate, as is most if not all of the early quadrajets pre emmissions.
I start seeing full manifold vacum use in 66 on the holleys, 3367's etc.
The way I am seeing it, ported vac source equates to more advance in as the throttle plates open, manifold source retards advance as throttle plates open.
What am I missing? Thanks for responding even though it appears an old wound!
Bill
Here maybe I will learn sumptin' and am more than willing to digress.
But I think you have it backward or our (my) terminology is flawed, I have a 65 350 hp car with the 2818, I see you have a 365, clearly the vacum advance is hooked up to ported vacum source on the metering plate, as is most if not all of the early quadrajets pre emmissions.
I start seeing full manifold vacum use in 66 on the holleys, 3367's etc.
The way I am seeing it, ported vac source equates to more advance in as the throttle plates open, manifold source retards advance as throttle plates open.
What am I missing? Thanks for responding even though it appears an old wound!
Bill
The 2818 carbs and pretty much all of them pre-emission used full manifold vacuum. You get full vacuum and therefore full vacuum advance at idle. Ported vacuum gives you zero vacuum and therefore zero vacuum advance at idle.
On a full vacuum system the more the throttle plates open up the the less vacuum you have. Ported vacuum works the same way of course because of the way vacuum is created BUT you have zero vacuum at idle, you get max vavuum advance with the plates JUST STARTING to crack open allowing the vacuum to develop in the carb, than from that point on will decrease the more the throttle plates open up.
The main difference is because of where the source of the vacuum is plumbed from.
On a full manifold vacuum connection the port is below the throttle plates so it always sees full vacuum level with the throttle plates closed. On a ported vacuum system the port is above the throttle plates.
Now, before you tell me that on carbs such as the 2818 have the connection nipple 1/2 or 3/4 the way up the carb body and therefore is above the throttle plate I already know that but the circuit that is open to the vacuum that goes to the nipple connection is below the throttle plate.
it's easy to determine if a connection port is full or ported vacuum. At idle just put your finger over the port and if you feel the vacuum on your finger you know it's full manifold vacuum. The 2818 carbs and pretty much most if not all on the pre-emission cars were full manifold vacuum. Ported vacuum only started with the emissions crap such as A.I.R.
The Q-Jets used later on the C3's were mostly ported until later on after the Cat converters were added as standard than they switched back to full manifold vacuum. My '78 is a later C3 with Cats of course and is full manifold vacuum also but pretty much almost all or all of the pre-car C3's were ported vacuum for emissions reasons. A LOT of people in the C3 section have switched their ported vacuum to full manifold vacuum because of the benefits of doing so.
01-22-2009, 04:19 PM
#49
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There ya are, Barry! I appreciate you joining in. Like you, I was trying to stay out of this thread, but there were a couple statements made that I just couldn't ignore, so I had to jump in. After having to keep explaining my reasonings here, I almost threw up my hands, and considered dropping you a PM for some support here.
Thanks for helping, and keep up the good work.
Thanks for helping, and keep up the good work.
01-22-2009, 04:55 PM
#50
Racer
nope, sorry, you are misunderstanding the system.
The 2818 carbs and pretty much all of them pre-emission used full manifold vacuum. You get full vacuum and therefore full vacuum advance at idle. Ported vacuum gives you zero vacuum and therefore zero vacuum advance at idle.
On a full vacuum system the more the throttle plates open up the the less vacuum you have. Ported vacuum works the same way of course because of the way vacuum is created BUT you have zero vacuum at idle, you get max vavuum advance with the plates JUST STARTING to crack open allowing the vacuum to develop in the carb, than from that point on will decrease the more the throttle plates open up.
The main difference is because of where the source of the vacuum is plumbed from.
On a full manifold vacuum connection the port is below the throttle plates so it always sees full vacuum level with the throttle plates closed. On a ported vacuum system the port is above the throttle plates.
Now, before you tell me that on carbs such as the 2818 have the connection nipple 1/2 or 3/4 the way up the carb body and therefore is above the throttle plate I already know that but the circuit that is open to the vacuum that goes to the nipple connection is below the throttle plate.
it's easy to determine if a connection port is full or ported vacuum. At idle just put your finger over the port and if you feel the vacuum on your finger you know it's full manifold vacuum. The 2818 carbs and pretty much most if not all on the pre-emission cars were full manifold vacuum. Ported vacuum only started with the emissions crap such as A.I.R.
The Q-Jets used later on the C3's were mostly ported until later on after the Cat converters were added as standard than they switched back to full manifold vacuum. My '78 is a later C3 with Cats of course and is full manifold vacuum also but pretty much almost all or all of the pre-car C3's were ported vacuum for emissions reasons. A LOT of people in the C3 section have switched their ported vacuum to full manifold vacuum because of the benefits of doing so.
The 2818 carbs and pretty much all of them pre-emission used full manifold vacuum. You get full vacuum and therefore full vacuum advance at idle. Ported vacuum gives you zero vacuum and therefore zero vacuum advance at idle.
On a full vacuum system the more the throttle plates open up the the less vacuum you have. Ported vacuum works the same way of course because of the way vacuum is created BUT you have zero vacuum at idle, you get max vavuum advance with the plates JUST STARTING to crack open allowing the vacuum to develop in the carb, than from that point on will decrease the more the throttle plates open up.
The main difference is because of where the source of the vacuum is plumbed from.
On a full manifold vacuum connection the port is below the throttle plates so it always sees full vacuum level with the throttle plates closed. On a ported vacuum system the port is above the throttle plates.
Now, before you tell me that on carbs such as the 2818 have the connection nipple 1/2 or 3/4 the way up the carb body and therefore is above the throttle plate I already know that but the circuit that is open to the vacuum that goes to the nipple connection is below the throttle plate.
it's easy to determine if a connection port is full or ported vacuum. At idle just put your finger over the port and if you feel the vacuum on your finger you know it's full manifold vacuum. The 2818 carbs and pretty much most if not all on the pre-emission cars were full manifold vacuum. Ported vacuum only started with the emissions crap such as A.I.R.
The Q-Jets used later on the C3's were mostly ported until later on after the Cat converters were added as standard than they switched back to full manifold vacuum. My '78 is a later C3 with Cats of course and is full manifold vacuum also but pretty much almost all or all of the pre-car C3's were ported vacuum for emissions reasons. A LOT of people in the C3 section have switched their ported vacuum to full manifold vacuum because of the benefits of doing so.
Barry,
Thanks for the swattin! Yes, it appears I had it *** backwards AND a misconception on the 2818's. So much for typing while I am still wakin up!
Thankfully so far when I have built something or a resto I get it right easier than getting it into text. this is an area that many people do not understand and I come up against cars with motors someone else built and hear all kinds of stories and misconcertions about what vacum controlled advance is there for. Most of my customers use their cars for street driving only, these are getting way to expensive to beat up, I cannot tell you how many times I convince a customer to allow me to reconnect or install a CORRECT vacum advance can after the "race" engine builder they used told them to leave it off and pluged, (usually the builder is told they want gobs of HP, he is never told driveability)after an appropriate tune for the street they are amazed at how well it performs.
Oh, and yes, some of them actually sit around and concern themselves with the mileage they are getting so I can even tell them that may improve also!
Anyway, thanks for taking the time!
Bill
01-22-2009, 05:01 PM
#51
Le Mans Master
There ya are, Barry! I appreciate you joining in. Like you, I was trying to stay out of this thread, but there were a couple statements made that I just couldn't ignore, so I had to jump in. After having to keep explaining my reasonings here, I almost threw up my hands, and considered dropping you a PM for some support here.
Thanks for helping, and keep up the good work.
Thanks for helping, and keep up the good work.
01-22-2009, 05:02 PM
#52
Le Mans Master
Barry,
Thanks for the swattin! Yes, it appears I had it *** backwards AND a misconception on the 2818's. So much for typing while I am still wakin up!
Thankfully so far when I have built something or a resto I get it right easier than getting it into text. this is an area that many people do not understand and I come up against cars with motors someone else built and hear all kinds of stories and misconcertions about what vacum controlled advance is there for. Most of my customers use their cars for street driving only, these are getting way to expensive to beat up, I cannot tell you how many times I convince a customer to allow me to reconnect or install a CORRECT vacum advance can after the "race" engine builder they used told them to leave it off and pluged, (usually the builder is told they want gobs of HP, he is never told driveability)after an appropriate tune for the street they are amazed at how well it performs.
Oh, and yes, some of them actually sit around and concern themselves with the mileage they are getting so I can even tell them that may improve also!
Anyway, thanks for taking the time!
Bill
Thanks for the swattin! Yes, it appears I had it *** backwards AND a misconception on the 2818's. So much for typing while I am still wakin up!
Thankfully so far when I have built something or a resto I get it right easier than getting it into text. this is an area that many people do not understand and I come up against cars with motors someone else built and hear all kinds of stories and misconcertions about what vacum controlled advance is there for. Most of my customers use their cars for street driving only, these are getting way to expensive to beat up, I cannot tell you how many times I convince a customer to allow me to reconnect or install a CORRECT vacum advance can after the "race" engine builder they used told them to leave it off and pluged, (usually the builder is told they want gobs of HP, he is never told driveability)after an appropriate tune for the street they are amazed at how well it performs.
Oh, and yes, some of them actually sit around and concern themselves with the mileage they are getting so I can even tell them that may improve also!
Anyway, thanks for taking the time!
Bill
There is enough false information, wrong information, and misconceptions out there already (plenty in this thread alone) so no need to add fuel to that fire.
01-22-2009, 05:08 PM
#53
Melting Slicks
nope, sorry, you are misunderstanding the system.
The 2818 carbs and pretty much all of them pre-emission used full manifold vacuum. You get full vacuum and therefore full vacuum advance at idle. Ported vacuum gives you zero vacuum and therefore zero vacuum advance at idle.
On a full vacuum system the more the throttle plates open up the the less vacuum you have. Ported vacuum works the same way of course because of the way vacuum is created BUT you have zero vacuum at idle, you get max vavuum advance with the plates JUST STARTING to crack open allowing the vacuum to develop in the carb, than from that point on will decrease the more the throttle plates open up.
The main difference is because of where the source of the vacuum is plumbed from.
On a full manifold vacuum connection the port is below the throttle plates so it always sees full vacuum level with the throttle plates closed. On a ported vacuum system the port is above the throttle plates.
Now, before you tell me that on carbs such as the 2818 have the connection nipple 1/2 or 3/4 the way up the carb body and therefore is above the throttle plate I already know that but the circuit that is open to the vacuum that goes to the nipple connection is below the throttle plate.
it's easy to determine if a connection port is full or ported vacuum. At idle just put your finger over the port and if you feel the vacuum on your finger you know it's full manifold vacuum. The 2818 carbs and pretty much most if not all on the pre-emission cars were full manifold vacuum. Ported vacuum only started with the emissions crap such as A.I.R.
The Q-Jets used later on the C3's were mostly ported until later on after the Cat converters were added as standard than they switched back to full manifold vacuum. My '78 is a later C3 with Cats of course and is full manifold vacuum also but pretty much almost all or all of the pre-car C3's were ported vacuum for emissions reasons. A LOT of people in the C3 section have switched their ported vacuum to full manifold vacuum because of the benefits of doing so.
The 2818 carbs and pretty much all of them pre-emission used full manifold vacuum. You get full vacuum and therefore full vacuum advance at idle. Ported vacuum gives you zero vacuum and therefore zero vacuum advance at idle.
On a full vacuum system the more the throttle plates open up the the less vacuum you have. Ported vacuum works the same way of course because of the way vacuum is created BUT you have zero vacuum at idle, you get max vavuum advance with the plates JUST STARTING to crack open allowing the vacuum to develop in the carb, than from that point on will decrease the more the throttle plates open up.
The main difference is because of where the source of the vacuum is plumbed from.
On a full manifold vacuum connection the port is below the throttle plates so it always sees full vacuum level with the throttle plates closed. On a ported vacuum system the port is above the throttle plates.
Now, before you tell me that on carbs such as the 2818 have the connection nipple 1/2 or 3/4 the way up the carb body and therefore is above the throttle plate I already know that but the circuit that is open to the vacuum that goes to the nipple connection is below the throttle plate.
it's easy to determine if a connection port is full or ported vacuum. At idle just put your finger over the port and if you feel the vacuum on your finger you know it's full manifold vacuum. The 2818 carbs and pretty much most if not all on the pre-emission cars were full manifold vacuum. Ported vacuum only started with the emissions crap such as A.I.R.
The Q-Jets used later on the C3's were mostly ported until later on after the Cat converters were added as standard than they switched back to full manifold vacuum. My '78 is a later C3 with Cats of course and is full manifold vacuum also but pretty much almost all or all of the pre-car C3's were ported vacuum for emissions reasons. A LOT of people in the C3 section have switched their ported vacuum to full manifold vacuum because of the benefits of doing so.
The 2818 will fool you because the vacuum connection is so high up on the carb that you think its ported. When I pulled my vacuum hose off at the can,I quickly found out that it is a full vacuum source.
01-22-2009, 08:29 PM
#54
I sent them an e-mail asking them why the use of vacuum advance would void the warranty. Here is their reply:
Thank you for the question! The timing on the engines is to be set at
no more than 34 degrees, and when vacuum advance is used it advances the
timing too much (high 30's - low 40's). Having the timing set too high
can lead to engine failure because of detonation.
no more than 34 degrees, and when vacuum advance is used it advances the
timing too much (high 30's - low 40's). Having the timing set too high
can lead to engine failure because of detonation.
01-22-2009, 08:40 PM
#55
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I sent them an e-mail asking them why the use of vacuum advance would void the warranty. Here is their reply:
Quote:
Thank you for the question! The timing on the engines is to be set at
no more than 34 degrees, and when vacuum advance is used it advances the
timing too much (high 30's - low 40's). Having the timing set too high
can lead to engine failure because of detonation.
Quote:
Thank you for the question! The timing on the engines is to be set at
no more than 34 degrees, and when vacuum advance is used it advances the
timing too much (high 30's - low 40's). Having the timing set too high
can lead to engine failure because of detonation.
