Vac advance, ported or manifold?

[Cdaniel]

What you need is the spring tension set to control the timing advance.
not just the movement travel amount.

20 Bucks for something that is alomst a must have item.
Might keep you from pulling your Hair out.


PB

Right you are, I should get off my posterior and get one today.

As for springs, yes that's part of the equation but, The mechanical springs don't act on the breaker plate. They act on the shaft cam. Springs don't control the total, just at what RPM it happens. Right? Now maybe the springs are still limiting travel at my problem RPM. I should look into that. But I really think its the added advance that the ported vacuum adds that is causing ping.

 

[pabear89]

Right you are, I should get off my posterior and get one today.

As for springs, yes that's part of the equation but, The mechanical springs don't act on the breaker plate. They act on the shaft cam. Springs don't control the total, just at what RPM it happens. Right? Now maybe the springs are still limiting travel at my problem RPM. I should look into that. But I really think its the added advance that the ported vacuum adds that is causing ping.

But you can control the amount and timing of the Advancement.
By adjusting the spring tension in the vac adv dashpot.
Where it comes into play and where it tops out for total adv.

PB

 

[bull999999]

What are you smokin? If the car is in neutral or park, are the rpms high?

If you are in park or neutral, all you need is a small bit of throttle to get high RPM. Really, are you some high schooler trolling?

 

[bull999999]

I don't believe you. Take a slow breath and reread your post. You say the ported shuts off at no throttle. It is supposed to. You say the manifold is more vac and that is why it idles better.

He didn't say manifold port has higher vaccum, he said they have the same amount of vaccum except when the throttle is close. I got the same results so why don't you just get your vaccum guage out and try it out for yourself?

In fact, Perfomance Distributers (http://www.performancedistributors.com) recommons that you hook use the manifold vaccum port with their DUI setup for cleaner spark plugs at idle as long as it doesn't ping. If you don't believe me, send them an E-mail at [email protected] and find out for yourself.

Somebody just put a gun to my head now please. I can't take it anymore. It idles better because you increase vacumm? Naw. It should idle better with no vacumm. Vacumm shouldn't change anything about the idle. You're not supposed to have vacumm at idle. Only at higher rpms. What do you need vac at idle for? The thing just sits there and idles! If you have idle problems, I'd suggest a carb adjustment or rebuild, or look at your points if you stilll have them, or faulty plug wires, etc. NOT low vacumm.

Before you accuse someone of "smoking" something, you should reread your own posts. Maybe you have a "special" engine that doesn't have any vaccum at idle but most of us have 16"hg of vaccum at idle or higher (lower if you have a wild cam).

 

[Ozsum2]

If you are in park or neutral, all you need is a small bit of throttle to get high RPM. Really, are you some high schooler trolling?

Does someone want to answer him?

 

[Ozsum2]

He didn't say manifold port has higher vaccum, he said they have the same amount of vaccum except when the throttle is close. I got the same results so why don't you just get your vaccum guage out and try it out for yourself?

In fact, Perfomance Distributers (http://www.performancedistributors.com) recommons that you hook use the manifold vaccum port with their DUI setup for cleaner spark plugs at idle as long as it doesn't ping. If you don't believe me, send them an E-mail at [email protected] and find out for yourself.



Before you accuse someone of "smoking" something, you should reread your own posts. Maybe you have a "special" engine that doesn't have any vaccum at idle but most of us have 16"hg of vaccum at idle or higher (lower if you have a wild cam).

I live at 10,200' and have the sea level equivelent of 23" of vacumm.

 

[351LX]

I don't believe you. Take a slow breath and reread your post. You say the ported shuts off at no throttle. It is supposed to. You say the manifold is more vac and that is why it idles better.

Somebody just put a gun to my head now please. I can't take it anymore. It idles better because you increase vacumm? Naw. It should idle better with no vacumm. Vacumm shouldn't change anything about the idle. You're not supposed to have vacumm at idle. Only at higher rpms. What do you need vac at idle for? The thing just sits there and idles! If you have idle problems, I'd suggest a carb adjustment or rebuild, or look at your points if you stilll have them, or faulty plug wires, etc. NOT low vacumm.

Anyone who owns a vacuum gauge knows that your motor produces 10-20 inches HG manifold vacuum at idle.You need vacuum at idle to pull fuel out of the carburetors idle and transition circuits when the throttle blades are closed.Once the throttle blades open up manifold vacuum decreases and venturi vacuum increases which pulls the fuel out of the boosters.I never said that manifold is more vac, I said once the throttle is open past a certain point manifold and ported vac are the same.If you hook your vacuum advance to to a ported source then you have less initial timing at idle but once you are driving down the road you have exactly the same amount of vac advance whether it is hooked to a ported or manifold source.The reason it idles better hooked to a manifold source is because you have more initial timing.Increase your initial timing of your distributor and see if the idle speed goes up,same thing.Ported vacuum came about because of emission controls as a means of increasing combustion temperature to decrease NOx emissions.I don't understand how venturi vacuum is even involved in a vacuum advance discussion as the vacuum source in your carburetor for either ported or manifold vacuum is located in the baseplate and has nothing to do with venturi vacuum.The next time you have your carb apart follow the passage in the casting to see where the vacuum source for the ported outlet is located and you will see that it is in the baseplate, not the venturi area so as a result it doesn't increase with more throttle opening but decreases.

 

[Ozsum2]

Anyone who owns a vacuum gauge knows that your motor produces 10-20 inches HG manifold vacuum at idle.You need vacuum at idle to pull fuel out of the carburetors idle and transition circuits when the throttle blades are closed.Once the throttle blades open up manifold vacuum decreases and venturi vacuum increases which pulls the fuel out of the boosters.I never said that manifold is more vac, I said once the throttle is open past a certain point manifold and ported vac are the same.If you hook your vacuum advance to to a ported source then you have less initial timing at idle but once you are driving down the road you have exactly the same amount of vac advance whether it is hooked to a ported or manifold source.The reason it idles better hooked to a manifold source is because you have more initial timing.Increase your initial timing of your distributor and see if the idle speed goes up,same thing.Ported vacuum came about because of emission controls as a means of increasing combustion temperature to decrease NOx emissions.I don't understand how venturi vacuum is even involved in a vacuum advance discussion as the vacuum source in your carburetor for either ported or manifold vacuum is located in the baseplate and has nothing to do with venturi vacuum.The next time you have your carb apart follow the passage in the casting to see where the vacuum source for the ported outlet is located and you will see that it is in the baseplate, not the venturi area so as a result it doesn't increase with more throttle opening but decreases.

I have my timing set at 13 DBTDC inital and anymore will cause it to stumble and ping under WOT.

 

[Ozsum2]

Simple, when your car's in park or neutral, or when going down a large hill in low gears.

Something must be wrong with my engine. When I am in park or neutral and apply little throttle, my engine isn't at a high rpm. And if I have low gears and go down a steep hill, the low gears keep the engine at a lower rpm. It keeps it from running away, and lets it lope down the hill.

 

[Max Power]

Lotta misconceptions here. 351LX is pretty close to spot on, although initial ported vacuum advance was introduced for fuel economy as well.

Dual diaphragm is truly an emissions stepchild. It runs through a thermal switch somewhere in your cooling system, usually on the stat housing on the radiator side of the stat, and it prevents vacuum advance to the distributor until the engine is at operating temp. When the switch is open, equal vacuum is applied to both sided of the diaphragm cancelling each side out, when it closes, just one side gets the vacuum and advances.

 

[JB66]

Wow! This has been a very interesting thread! Please correct me if I'm wrong, but isn't the vacuum advance used to prevent stumble on acceleration until the mechanical advance 'catches up?' Vacuum advance should never (read, will never) take the place of a properly set up mechanical advance curve. Why don't race engines have vacuum advances if they could, then? Pinging under partial throttle results from timing too advanced , thus 'detonation' from the plug firing too early in the stroke. Partial throttle pinging means that the VACUUM advance is allowing to much advance to be added to the current rpm mechanical advance plus the basic timing. Equation... Vacuum Adv. + Mechanical Adv. + Base Timing = Total Advance for ANY given rpm. The only part that varies with throttle opening is the Vac. Adv. Most distributor vacuum advances (single piece units) are adjusted using a 1/8" allen wrench inserted into the Vac. hose connection. Try adjusting the advance until the pinging decreases. You can go crazy trying to adjust timing advance by rerouting vacuum hoses!

 

[Ozsum2]

Wow! This has been a very interesting thread! Please correct me if I'm wrong, but isn't the vacuum advance used to prevent stumble on acceleration until the mechanical advance 'catches up?' Vacuum advance should never (read, will never) take the place of a properly set up mechanical advance curve. Why don't race engines have vacuum advances if they could, then? Pinging under partial throttle results from timing too advanced , thus 'detonation' from the plug firing too early in the stroke. Partial throttle pinging means that the VACUUM advance is allowing to much advance to be added to the current rpm mechanical advance plus the basic timing. Equation... Vacuum Adv. + Mechanical Adv. + Base Timing = Total Advance for ANY given rpm. The only part that varies with throttle opening is the Vac. Adv. Most distributor vacuum advances (single piece units) are adjusted using a 1/8" allen wrench inserted into the Vac. hose connection. Try adjusting the advance until the pinging decreases. You can go crazy trying to adjust timing advance by rerouting vacuum hoses!

Nope. I ran my dist for a month while waiting for my new one to show up. Just plugged the old line. No difference except loss of economy.

 

[JB66]

Is your harmonic balancer one of those with the pulley attached to the main balancer by a thin film of rubber? I've heard that these can 'slip' over time and age and cause improper camshaft installation as well as impossible timing situations. To check this, the engine must be set with the crankshaft keyway straight up. The timing mark should then be pointing to the 0* mark on the balancer. Let us know. Also, does the engine ping with the vac. adv. hose disconnected and plugged?

 

[351LX]

At WOT vacuum going to the vacuum advance should be almost nothing so the vacuum advance shouldn't be contributing to the total amount of advance.If it is pinging at WOT but your engine responds to a lot of initial advance there is an easy modification you can do.On stock Ford distributors under the plate where the points or pickup is located there is the mechanical advance assembly which consists of some weights,some springs and a slot which limits the amount of mechanical advance.There will be two different slots opposite from each other,usually marked something like 10L and 15L.If you double the number it gives you the approximate number of degrees of mechanical advance (ie the 10L gives you 20 deg, the 15L gives you 30 deg).Most distributors use the larger slot, if you change to the smaller one then you can run more initial timing without changing your total amount of advance as the amount of mechanical advance will be less.Right now on my car I am running 14 deg of initial timing but my total is only 34.If you do this modification with the distributor in the engine remember that the rotor will end up 180 deg from before so you have to rearrange your plug wires to match.

 

[brianj5600]

MSD and crane both say ported. I'm not going to read all this, but mine will stay on the ported fitting.

 

[bull999999]

Something must be wrong with my engine. When I am in park or neutral and apply little throttle, my engine isn't at a high rpm. And if I have low gears and go down a steep hill, the low gears keep the engine at a lower rpm. It keeps it from running away, and lets it lope down the hill.

Yeah something must be wrong with your engine since I can easily do 3000+ RPM with about a 1/4 throttle in any car I've in while it's in park or neutral.

Let's say that you are going down a steep hill in low gear at high RPM. You close the throttle. Even though your RPM will go down eventually, but there will be a period where you're engine will be experiencing high RPM with a closed throttle. Heck, this is true even on a flat road. Why do you think that there's a spike in vaccum after doing WOT at a high RPM and then closing the throttle?

 

[Max Power]

""Please correct me if I'm wrong, but isn't the vacuum advance used to prevent stumble on acceleration until the mechanical advance 'catches up?'""

Nope. Acceleration is your lowest vacuum point, thus your least amount of vacuum advance.

""Is your harmonic balancer one of those with the pulley attached to the main balancer by a thin film of rubber? I've heard that these can 'slip' over time and age and cause improper camshaft installation as well as impossible timing situations.""

Close, but nope. The slipping rubber may throw off your initial timing setting, but cam and crank timing is set by the woodruff key in the crank. The harmonic isn't even on the car when doing a cam swap.

 

[Ozsum2]

Yeah something must be wrong with your engine since I can easily do 3000+ RPM with about a 1/4 throttle in any car I've in while it's in park or neutral.

Let's say that you are going down a steep hill in low gear at high RPM. You close the throttle. Even though your RPM will go down eventually, but there will be a period where you're engine will be experiencing high RPM with a closed throttle. Heck, this is true even on a flat road. Why do you think that there's a spike in vaccum after doing WOT at a high RPM and then closing the throttle?

I was being sarcastic. Nothing is wrong with my engine. It all depends on what the initial speed is when going down a steep hill. That wasn't stated.

 

[Ozsum2]

At WOT vacuum going to the vacuum advance should be almost nothing so the vacuum advance shouldn't be contributing to the total amount of advance.If it is pinging at WOT but your engine responds to a lot of initial advance there is an easy modification you can do.On stock Ford distributors under the plate where the points or pickup is located there is the mechanical advance assembly which consists of some weights,some springs and a slot which limits the amount of mechanical advance.There will be two different slots opposite from each other,usually marked something like 10L and 15L.If you double the number it gives you the approximate number of degrees of mechanical advance (ie the 10L gives you 20 deg, the 15L gives you 30 deg).Most distributors use the larger slot, if you change to the smaller one then you can run more initial timing without changing your total amount of advance as the amount of mechanical advance will be less.Right now on my car I am running 14 deg of initial timing but my total is only 34.If you do this modification with the distributor in the engine remember that the rotor will end up 180 deg from before so you have to rearrange your plug wires to match.

No, there's nothing wrong here. At 13DBTDC, that is the max on my initial timing to keep it from pinging. With the old dist, the weak springs in combination with the vac advance had my timing greatly advanced.

 

[Ronstang]

""Please correct me if I'm wrong, but isn't the vacuum advance used to prevent stumble on acceleration until the mechanical advance 'catches up?'""

Nope. Acceleration is your lowest vacuum point, thus your least amount of vacuum advance.

Manifold vacuum is lowest during acceleration and ZERO during WOT.....but ported vacuum is zero at idle and increases with RPM because it is created by air rushing through the venturi of the carburetor and during acceleration the volume of air going through the venturi and it's speed is increasing thus making ported/venturi vacuum highest under conditions when manifold vacuum is lowest or zero.....THIS IS WHY THE VACUUM ADVANCE CONNECTS TO PORTED VACUUM.

Regardless of all the misinformation in this thread total advance is: Initial timing + Mechanincal Advance + Vacuum Advance. The vacuum advance is not supposed to be dropped out at WOT as it would be if manifold vacuum was used, but ported vacuum is highest during WOT and it keeps the vacuum advance in the equation....as it should. Any distributor that has vacuum advance has LESS mechanical advance than a comparable distributor with only mechanical advance in order to keep the total advance the same. Where people run into problems is that after doing engine mods like cams/heads/exhaust which allow for and may require more initial timing they fail to recurve the mechanical advance to reduce it by the same amount they increased the initial timing. ALMOST NOONE EVER MESSES WITH THE MECHANICAL ADVANCE.....and this is the problem that creates all the confusion and misinformation.