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Discussion Starter · #1 ·
On the Carter BBD (non electronic) does it matter where the vaccum advance plugs into on the carb. All the other vaccum lines are not going to be in use because emissions have been stripped. Which outlet should the advance be routed into? What exactley does the advance do?

1987 YJ Laredo
Rylan D.
 

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The vacuum advance should be connected to a 'Ported' vacuum source.
The 'Ported' vacuum source is always above the base plate of the carburetor.
(up on the carburetor body somewhere)
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The vacuum advance adds timing advance that is directly related to air flow (and fuel flow) through the carburetor.
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'Ported' vacuum rises when airflow through the carburetor is increased, IE: when the throttle blades are open. (opposite of manifold vacuum in most cases)

'Ported' vacuum is taken from the carburetor venturi necks, and NOT the intake manifold.
The intake builds vacuum when the throttle blades are closed.
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If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 
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Discussion Starter · #3 ·
TeamRush,
Help me out here...the way I understood how it was supposed to work is as follows...

1. The mechanical advance increases the ignition advance as engine RPM increases.
2. The vacuum advance adds additional advance based on engine loading...i.e., at low throttle, manifold vacuum is greatest, hence, low loading. As you step on the gas, vacuum drops, so does advance. This helps prevent some of the pre-ignition. In other words, we want as much advance as possible without pre-ignition....and as we step on the gas, we want to retard that advance to prevent pinging. If we use ported vacuum, advance would increase under heavy accel. Basically, they vacuum advance ends up doing the same as the mechanical. Is this what we really want?

I'm not an expert, so I'm just asking.....

John......southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Locker, Solid Axle's, Durabak
 

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There are three different vacuum ports. Manifold vacuum, basically what is in the manifold. The second is ported. It is almose exactly as manifold, except there is no vacuum at idle. The ported signal is just above the throttle plates, so when the throttle plates are closed, there is no vacuum, and when the throttle is cracked open, it will give a manifold signal. The third is called "venturi vacuum". This source is primarily used for e.g.r. valves and e.g.r. valve amplifiers. This is the port that Rush was talking about. Do not hook your dist. advance up to a venturi signal! There is almost no vacuum at a venturi vacuum port until the volecity through the venturis is high. This port will only give a maximum of about 6 or 7 inches.

Usually you want to hook your dist. vacuum to a ported signal. A dist. vacuum advance is primarily for fuel economy. It has very little to do with horsepower, because under hard acceleration there is no manifold vacuum. Horsepower is more related to base timing plus centrificial advance. I live at high altitude, so things up here are a little bit different. We usually advance our timing about 4 degrees to help raise manifold vacuum. If the dist. vacuum advance was put on a "manifold" signal, there would be too much advance at idle, and the engine would want to misfire.

 

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Didn't ported vacuum become popular in the "pollution era" (72-74)? I believe GM used an electric block for ported vacuum, on some models, until top gear was achieved.....Ford used a vacuum delay valve inserted inline.....I don't recall Chryslers technique. At the time most of us plebes hated the pollution controls and their effect on performance ......(ported vacuum being one of them)...the instructor finally hit it into our heads that you have no manifold vacuum at decent throttle anyway. Hence with the electric vacuum block..you didn't get any advance until the ported vacuum was in a useable range. I believe that dorfs is correct about the venteri vacuum being relatively low.....but somewhat in proportion to the ported.

GeeAea

Figures don't lie ....... but liars sure do figure.
 

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Pretty much, The reason that you con't remember Chryslers attempt was the advent of the "lean burm" computer on the air cleaner. Everything was done electrically.

 
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Discussion Starter · #7 ·
so for a vaccum gauge, where should that be connected?

1987 YJ Laredo
Rylan D.
 

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I see dorfs is trying to get something started with out knowing the subject again...
Too bad.
He's always trying to stir the stink pot instead of learning something... and he seems to have a real problem with me.
I guess he feels threatened.

I just wish he would learn the subject, instead of post misinformation, dis-information, and outright false hoods.
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Someone at Holley has been watching the posts here, and the fine people at Holley and provided written permission for me to use their drawings and graphics in my tech articles. This is the second place to do so. (I must be doing something right!)
Thanks to Steve C. at Holley! The disk will come in handy here, and for my upcoming Jeep Tech Upgrades Disk...
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*TeamRush,*
*Help me out here...the way I understood how it was supposed to work is as follows...*

*1. The mechanical advance increases the ignition advance as engine RPM increases.*

Correct. Centrifugal advance is directly tied to engine rpm by a set of swinging weights that add advance as the distributor shaft rotation increases and slings the weights out.
The weights have springs attached to them to bring them back in when the engine slows.
By running lighter springs, the advance comes in sooner because the weights can be spun out faster.
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*2. The vacuum advance adds additional advance based on engine loading...i.e., at low throttle, manifold vacuum is greatest, hence, low loading.*

Incorrect assumption.
Manifold vacuum has very little to do with ported vacuum for the vacuum advance.
This is not recognized by the average Joe, and that's why so many vacuum advance sources incorrectly come from the intake.
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*As you step on the gas, vacuum drops, so does advance.*

Incorrect assumption.
As you step on the gas, manifold vacuum drops.
Ported vacuum draws it's vacuum source from the carburetors venturi body, where vacuum is just starting to really build.

If you want to prove it to yourself, hook a vacuum gauge and a timing light to your engine.
Start the vehicle.
Throw the throttle blades open, watch what happens to manifold vacuum (It drops), and watch what happens to the ignition (it advances).
The ignition will stay advanced no matter if the throttle is held in an half open position or revved up more to full throttle.
That is because the more air flow through the carburetor is increased, and the ported vacuum is increased with the airflow.

If you let the engine return to normal idle, or close the throttle blades suddenly, the air flow will all but stop, and the ignition timing will retard.
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*This helps prevent some of the pre-ignition.*

'Pre-Ignition' is a term that was much over used a few years ago, and simply means the charge mixture burned too soon.
'Pre-Ignition' is a misnomer anyway. Either you have ignition or you don't. There is no 'Pre' about it...
It may be too soon, but it's not 'Pre'.

Most of what is called 'Pre-Ignition' is good old fashion Detonation.
The only time you can use the term 'Pre-Ignition is when a sharp edge, or a burr left over from machining, or something like that protrudes into the cylinder and becomes red hot. When the charge mixture enters the cylinder-- BOOM- the hot spot sets off the charge.
That is the ONLY correct use of 'Pre-Ignition'.

You can fire the cylinder too soon with the ignition, but thats not 'Pre'. That is the ignition working correctly, and firing at the time it was supposed to, just a nit-wit adding too much advance too soon. Thats human error, not 'Pre Ignition'...
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*In other words, we want as much advance as possible*

Correct, with a reservation...
The sooner we can fire the cylinder, the longer the cylinder has to burn, heat the gasses, the gasses expand, push down on the piston, and make power...
If we fire the cylinder too soon, the piston and connecting rod get shoved back the way they came instead of breaking over the crankshaft.
When that happens, we call it detonation. Detonation will hammer the pistons right into the oil pan in a hurry!
We want as much advance as we can get with out detonation.
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*and as we step on the gas, we want to retard that advance to prevent pinging.*

No. We want the advance to ride that fine line just before detonation.
If you retard, you will loose power when you try to 'step on the gas' or move off the line as we say in the business. Advance isn't all the way in yet, because the air flow through the venturies hasn't picked up enough yet...
The timing isn't retarded, it just hasn't advanced fully yet...
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*If we use ported vacuum, advance would increase under heavy accel.*

Yes it would, but not the way you are thinking. The engine uses X amount of air per revolution. It will use a little more when the intake isn't restricted by the throttle blades.
The amount of advance is linked to the amount of air passing through the venturies.
If the engine is just starting out under the worst of the load, trying to get it moving at low engine RPM, then the air flow is going to be slow (low horse power to weight ratio), so the advance is going to be small.

When the engine starts to get up in the RPM range a little, and starts making some horsepower and torque, the horse power to weight ratio comes up, and in effect, makes the load easier to move. As the RPM comes up, the engine comes up, but the intake vacuum is still way down, but the air volume through the venturies comes up, and the advance also comes up... and stays up until you close the throttle blades and cut the air flow off...
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*Basically, they vacuum advance ends up doing the same as the mechanical. Is this what we really want?*

It doesn't do the same thing as the mechanical advance. The centrifugal advance adds a set amount of advance at a set RPM, for about half of the total advance and engine gets.

The Ported vacuum advance system is load and engine RPM variable to an extent.
It is also very sensitive to atmospheric conditions and changes.
Cool, dense air, like on a rainy night, will cause the advance to come in sooner. The dense air creates more vacuum for any given CFM through the carburetor.
On hot, thin air days, the effect is reversed, and not as much vacuum is created, so the advance is smaller for the given CFM through the carburetor.
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It's an ingenious system really, and much too complicated for me to cover fully here.
It does work though, and has worked very well for many years...
I have only met a hand full of people (maybe 2 dozen) through the years that honestly and truly understand it, and know what they are talking about...
Lots of people think they do though, that's why so many people are misled about ported vacuum and how a vacuum advance works...

You can see what I mean by the opinions on this thread already...
Hope this helped answer your questions.... Aaron.

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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I see dorfs is trying to get something started with out knowing the subject again...
Too bad.
He's always trying to stir the stink pot instead of learning something... and he seems to have a real problem with me.
I guess he feels threatened.

I just wish he would learn the subject, instead of post misinformation, dis-information, and outright false hoods.
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You know, I'm not "stirring the pot" and I most certainly not threateded or have a problem with you. I was just stating the way I was tought. I'm not ignorant to the subject, I have been a licenced emission mechanic for the last 24 years, and do nothing but drivability for a living. While it seems everybody wants to remove the "emissions crap" from their viehicles, I have been putting it back on! Over the years I have been tought by the state of Colorado, Ford, GM, and Chrysler. Why the hell would I want to post misinformation, dis-information, and outright false hoods?

I have never dogged anybody on this board, called them stupid, or tried to steer them wrong. I guess part of freedom of speech is not having to believe everything that you read and not having to believe everything that somebody tells you. I mostly read through these posts to get ideas and methods of improving my Jeeps, which have been great. So you can continue to "flame on" and I will gracefully step aside.

John Dorflinger, another right wing conserative

 

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So, is what you were trying to say was,...
You were taught wrong?,
You weren't taught enough?,
You thought a simple answer to a simple question wasn't adequate?,
You just want confuse people that ask simple questions with complex, and often wrong, answers?,
You are frustrated that all you do is emissions for the past 24 years?,
You thought I needed help with a simple question?,
You just have to say something, even if it's wrong?,
Just don't like me?,
All of the above?
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I have been with the Ford, GM, and Mopar people too.
I worked WITH them on one project or another, not sat in emissions classes under them.
I'm equally sure The Mopar Muscle team, the Ford SVO guys, And GM's Thumper Program guys weren't teaching emissions...
I've also taken classes with, or worked for Mahl, Cosworth, Holley, Carter, Doug Nash, Jasper Engines, NOS, Autotronic Controls (MSD), BDS, World Of Performance, Goodyear, and a dozen others.
I too have been doing this for over 25 years, but my career started at Indy working on champ cars, and USAC sprint cars.
When I started, Firestone tires were the king of the track, and a four cylinder Offy could run at Indy....
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Knowing were ported vacuum is, and what it does is basic stuff. It's even taught in the local High School Auto Shop, because I supplied the cut away carbs for the program.
Don't get mad at me because you didn't know what it did, or where it was taken from.
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Just like you saying exhaust gas adds horsepower... The EGR discussion...
I still never figured out your thinking on that one...
I still don't see how burned, spent, inert exhaust gasses are supposed to create any horsepower on the second time through the combustion chamber...
I also noticed you abandoned that thread when I asked the hard questions...
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You didn't have to post, and you didn't have to directly contradict me.
You also didn't have to muddy the water with and explanation the beginners couldn't understand, and the pro's can pick apart as BS.

If you would have said, 'I learned it THIS way...', there wouldn't be a problem...
A gentle correction, or explanation, but no problem...
I've never jumped on anyone that was asking a question.... Just the wise guys...

And if you think I'm going to lay still while you poke me with a verbal stick, you are dead wrong.
If you don't want me to fall on you, Be correct, Be quiet, or post on a BBS I don't.
Most of all, be polite, or you will hear from me again....





If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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TR....I think that you read too much into some of this stuff. Your experience seems mostly with racing applications. You appear to have an abudence of knowledge on this type of thing. This does not say that you know ALL. dorfs is a man of much talent as well (l BTW am a lesser man than either of you ....in this forum anyway). His point of the EGR discussion was that the recirculation of inert exhaust gas allows the engine to run at a higher output without detonation WITH FULL EMISSIONS COMPLIANCE.......which in most cases you, in a RACE application, throw entirely out the window. Without EGR, and with current emissions standards, we would be driving around in vehicles powered by Briggs & Stratons because the NOX output would be too high for any reasonably powered vehicle. His reference to "drivability"(the term that replaced performance in the mid '70's) is the "art & science" of getting a clean running engine to perform at its best.

So, is what you were trying to say was,...
You were taught wrong?,
You weren't taught enough?,
You thought a simple answer to a simple question wasn't adequate?,
You just want confuse people that ask simple questions with complex, and often wrong, answers?,
You are frustrated that all you do is emissions for the past 24 years?,
You thought I needed help with a simple question?,
You just have to say something, even if it's wrong?,
Just don't like me?,
All of the above?
This type of stuff is uncalled for.......why you insist on doing it EVERY TIME someone disagrees with you I don't know. What composite emotional substrata occupies your mind that could cause such an almost automatic hostile reflex? He said nothing of the sort......he made no personal attack on you.....but you choose to blast anyone who has a different twist on things. You're the one who is not social here. Look back upon your posts.....you walk around boasting (most of it well earned I'm sure) about all your achievements ......and all it takes is one piss ant like myself to rattle your cage. You are the insecure one my man. Only someone who is in fear of being toppled could take such offence. With you it is never enough to just say "I don't agree with that"......you have to go on the attack and try and make the other person look like a jack-ass. Many members don't post on anything that you're involved in just because you can't resist slamming (if you don't believe me do a search on Team Rush and see). YOU have turned this into an unfriendly environment.

Put it back in your pants and stop making everything a pissing contest. You're a sharp man......but the sharpest that I've run into are smart enough to realize (and grown up enough to live with the fact) that they don't know it all.

GeeAea

Figures don't lie ....... but liars sure do figure.
 

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GeeAea, Check the location of your nose.
This is the third time I have found it in my business...

Just in case you haven't checked the posts, like you suggest, this is 11 times dorfs has directly contradicted me.
At first I ignored it, then I gave the rattle before the strike, that is above...
I get tired of someone asking a general and simple question about something, giving and answer appropriate to the question, and them someone calling me an idiot, and giving a long drawn out answer on some very specific topic, and drawing to an incorrect conclusion.
(like SVO EGR for example, when the topic at the time was cam timing)
If he wanted to add that overlap could add to emissions, that is OK, but cam profiles was the topic at the time.
To say in a public forum that my information was dated from the 40's and I had no idea what I was talking about. (Exactly what he implied)
He does emissions. I hope he's VERY good at it. If I did exactly the same thing for 24 years, you bet I would be VERY GOOD at it.

I have been doing what I do for more than 20 years. I am very good at it. I fully intend to be the very best in my field. Trying for anything less would make me one of the people I have to push out of my way every day, and I would be betraying myself.

I DO NOT attack anyone that disagrees with me. You should check the posts, especially for those that pumped Jacobs products or GM HEI's.
I did a really good job not making this personal. I didn't question his intelligents, I do question his education, especially concerning the basics, the very fundamentals.
I did not attack his family, like some of you have done me. I didn't attack his genetics.
I just get sick of people telling me that I'm full of it because his sister's cousin's brothers' barbers kid took a ASE test one time, and he says....

I have respect for dorfs on his knowledge on emissions. Several here say he's very good at getting emissions stuff up and running so they can pass the tests.
If he, you or anyone else has anything to add to anything I post, by all means, please do.
Make sure your information is correct, or I WILL correct you.
If you choose to stick your fingers in the fire again after that, expect to get burned...

I DON'T have much respect for anyone that sticks a nose in where it doesn't belong.
I have NO respect for anyone that piles on someone.

I also normally take issue with anyone that refers to themselves as a 'Piss ant'...
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*GeaAea* wrote,
*What composite emotional substrata occupies your mind that could cause such an almost
automatic hostile reflex?*

Lets see if I can make this perfectly clear...
My 'emotional substrata' is that of some one that doesn't take, or make excuses, and let me make this clear,
IT'S NONE OF YOUR DAMN BUSINESS.
If you attack me again on a personal level, it will get ugly in a hurry.
This is YOUR rattle...

Take it for what you paid for it... (I am your statments.)

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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Ok.........as you wish...my nose is where ever I choose it to be TR........this is not your board. You've claimed some delusional "squaters rights" as some authority here (and without a doubt.you are an authority). You're a flamer......you are incapable of being civil and always choose the hostile response to anything you don't see as "regal and scholarly enough" for your tastes. You are a miserable person and you bleed that poison into every post you make. Your ego is suspended at the direct expense of others. You are so full of yourself that you see nothing wrong with being the miserable vindictive retalatory maladaptive SOB that you are. You've had the good fortune to be blessed with brains and much skill ....but the cost you have paid is the price of a soul. I pity such a person with such talent that obviously lives with such daily pain of the shreaking nothingness of their life. You have to live with the demons that obviously dwell within you that you so easily allow to surface on a regular basis. You spend most of your time in love with yourself......probably because no one else can.
Lonely at the top.....ain't it TR

BTW....when I refered to myself as a piss ant....it was just to beat you to the punch before you told all of us once again how smart and experience and great and knowledgable..you are.and on and on. and how stupid...ignorant....undereducated....and all the things you usually say about someone who opposes the "great and wonderful Team Rush" (visions of Oz "Ignore the man behind that curtain")

GeeAea

Figures don't lie ....... but liars sure do figure.
 

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...and who was it who said that the "off-topic" posts lead to the flames and bashing of everyone? /wwwthreads_images/icons/laugh.gif

Anyone wanna talk about Moonguys? CJDave? /wwwthreads_images/icons/laugh.gif

Pete. /wwwthreads_images/icons/smile.gif

88YJ,4"susp,33"BFGMT,9kwinch,homemade swingout,258,999,4.10,weber32/36,GMHEI,one moonguy/wwwthreads_images/icons/smile.gif
 

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You know, if you would put half as much effort into learning something out of these postings as you do roaming around looking for these unoriginal editorials you copy and use on me, you might actually learn something...

Your posting sounded heart felt, but it had to be your heart you were speaking of.
Mine is doing just fine, except for a little high cholesterol and the fudge bar I just choked down...

This is pointless for me, and I'm not going to waste any more of my time on it...

You are borrowing second hand trouble. That makes you second banana, and I never deal with underlings... It's a waste of my time.

Go back to the Dr. Joyce Brothers page, or where ever you clipped that spew from, and see what else you can find to occupy you, because I grow bored with it, and now you have to play with yourself again...

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 
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