Good video. One of the better ones I've seen on the subject. I ran a scanner on my 2011 truck and noticed that the computers ignition timing was at 31 deg. advanced when idling. Just like if the vacuum advance canister was hooked to manifold vacuum, if it had one.I agree that the difference is at idle. At a certain point off idle, ported and manifold have the same vacuum. The vacuum canister on my car doesn't start advancing the timing until 7 inches of vacuum is present and maxed out timing at 16 inches. 20 degrees total advance. I also have a gm vacuum canister that is maxed out at 7 inches of vacuum. If you change your cam and that changes your manifolds vacuum, you will need to change your vacuum canister. No use having a canister that maxes out at 17 inches of vacuum when you're only making 12 because of the new cam. I've ran ported and manifold. Right now I'm running manifold. I've heard the argument that you don't want manifold vacuum because the vacuum/timing decreases when you accelerate. We'll it does but vacuum doesn't go to zero unless you floor it. Don't you want timing to decrease when the mixture in the cylinder gets more dense? Just my 2 cents
Someone that actually understands it. Ive commented on several other of these videos that ported and manifold are exactly the same, just that ported is switched anove the throttle blades. Not taking into account emissions, both can be tuned to do exactly the same thing, it just depends on how you set up your mechanical advance and initial timing. And just as you stated, connecting to manifold does make them idle better and feel snappier with no load, but put it in gear and crack the throttle and all that advance instantly dissappears until the mechanical advance starts to come in.
Very good explanation of vacuum vs ported. I was having issues with mine getting hot in stop and go traffic. After watching a lot of the videos I tried hooking to manifold vacuum. That solved my problem. I know longer get hot in traffic. I think the answer to everybody’s question is try it both ways and see what works best for you. Also I gained 2 to 3 mpg on the hwy. city driving still sucks. Lol
You are absolutely right in what you say. Have also wondered why some "experts" think you should have vaccum advance all the time. If the engine needs more ignition at idle, the mechanical setting changes instead. The last thing you mention is also very important on an engine with a hot cam, idling will be even worse if the ignition also starts and "rocks" as well
Great Video, Makes great sense. So basically those that enjoy the Manifold port are enjoying the better Idle Quality because of the added timing by the can. But they sacrifice the loss of timing at the point the throttle is cracked open. If you chose to use port, you can still benefit from a Nice Idle quality by setting your mechanical advance to more (preferably using a vac gauge to monitor max vac signal). I'll continue with the port setup but dial my mechanical to what the engine likes with the gauge for a smooth idle. My plugs look rich, so I think Ill try going from 12° to 14° or more if required, we'll see.
There is a myriad of variables as to which vac take off is more suitable and it is always combination specific. As a general rule I prefer ported vacuum but I always test straight vacuum aswell. Whatever the particular combo works best with, is absolutely the right way to have it set up 👍
Also when you close the throttle at high rpms, the ported signal will be zero. I've tried it both ways and my motor runs noticeable cooler with manifold vacuum. Probably less chance of burning an exhaust valve too.
Well if you want vacuum advance at idle because of a larger cam then you need manifold vacuum. Some set-ups do better on manifold. So it just depends on the amount of timing and where the engine wants it.
Depends on which vacuum canister is installed on your distributor. They switched to ported vacuum for smog engines to make the exhaust manifolds run hotter. A canister calibrated for manifold vacuum is all-in with just a few inches of vacuum whereas a ported canister requires more vacuum, usually 7inches or more. If you connect a ported canister to manifold vacuum, timing drops out with throttle tip-in.
My 75 Lincoln with 460 was not happy until I dialed in 38deg with manifold vac at idle. This new ethanol fuel burns different than the old stuff. It also doesn't help my engine is probobly 7-1 compression with zero quench (thank you malaise era engineering). Maybe my damper has shifted but that's the number where it finally idled good.
I think most of these guys try to avoid properly curving a distributor by hooking the vacuum advance up to manifold. My 8.1:1 440 in my 4700lb 1986 Dodge 4x4 Ramcharger has 20* initial, 38* mechanical total, and 18* ported vacuum for a total of 56* at cruise. At Idle, it pulls 19" of vacuum, tested with 3 different gauges. I built it for low and mid range torque, cruise @ 60mph is 2,100rpm. I get 19 mpg. Instant throttle response with a Thermoquad from idle through any part of the rpm range. No pings on 87 E10. With a 1200 stall converter that actually stalls at 1400, I whack the gas and it JUMPS.
Question…. Any troubleshooting tips you could give me on why I’m getting 15-20 lbs of vacuum at idle on my ported port? When I try an take it to square with my idle screw it just kills engine. My timing is maxed also due to detonation. Timing 12-33
Throttle blades are open too far - what kind of carburetor are you using? What do you have for a cam, and is it 12 degrees with the vacuum advance plugged in or without?
@ summit 600… cam is part of the eldebrock performer package. Yes 12 degrees initial without vacuum advance. I’m not using vacuum advance at all by that’s not relevant at this point. Just answering you! Thanks for helping
Ported vacuum is NOT manifold above the throttle blades. Manifold vacuum is created by the pistons displacing air. Ported is created by the Venturi effect of air flowing past that port above the throttle blades. There is no debate amongst those who understand the difference. For street/strip applications you use manifold vacuum for your advance. Ported is for emission controled vehicles. End of story.
The video is aimed exactly at people like you. What you’re describing is the venturi signal that activates the vacuum secondaries on a Holley style carburetor. You do not understand how it works and should watch the video again. Your incorrect explanation is exactly why people seem to think ported vs manifold vacuum will affect anything but their timing at idle. I’m sure you do too. Buy a timing light and check for yourself, but prepare to be upset by the reality.
@@426440yes, just like how a vacuum secondary works, and like how a fuel metering circuit. The Bernoulli's principal. That port in the throttle bore is situated where it is for a reason. And it's not to expose it to manifold vacuum. It's where air velocity is high between it and the throttle blades. But unlike a fuel metering circuit or vac secondary the signal diminishes once the throttle blade moves past it. But you believe what you want, bro.
It’s not about believing what I want, it’s knowing how it works. The signal doesn’t diminish as you open the throttle blade, it matches the manifold vacuum signal. I demonstrate this in the video. The irony is that it’s YOU believing what you want, when it’s clear you’ve never actually checked how these function. But keep believing that switching from one to the other is changing your timing curve at anything other than idle. It doesn’t actually matter, because both will provide the same vacuum and additional advance at WOT, zero. And they will match at part throttle and every other non-idle condition. I understand how you are explaining you think it works, but there is a reason that the signal for the vacuum secondary canister on a Holley style carb is at the top of the venturi (like a booster is), and there is also a reason it protrudes into the venturi and is shaped like it is.
@@426440 how the vacuum is created is bit of a moot point. The more important point to make is, you do not use ported vacuum on a vacuum advance for street applications. It does not apply timing advance at idle when it needs it. High vacuum = need more advance. Ported was an emissions era strategy and nothing more. Would highly recommend finding the article by John Hinckley "Timing and Vacuum Advance 101".
Hi there I looked into this topic a lot, my original 350 which I tune on ported which I like it this way, but originally it came on full vacuum I did not give a chance to tune on it, I have full stock setup , what you think?
Manifold vacuum only! Set your initial timing on about 15 if you have an HEI which will give you 34-35* total. Get a spring kit and use whatever springs give you all in centrifugal timing by 2500 rpm. Make sure your distributor is in phase also. Best to use an aftermarket vacuum canister and adjust the stroke to give a good 15* of advance under full manifold vacuum and adjust the rate spring as aggressive as you can without any audible detonation! If you have a factory HEI the modules crap out around 5000 rpm so if you rev higher get a good aftermarket ignition module! When you get your ignition setup properly then tune the idle mixture and curb idle on the card and when you get it right, the engine will be extremely responsive....
Well 3248 people have witnessed your improper tuning technique! Take a look around on TH-cam....there are expert performance guys with decades long resumes that will tell you “manifold” vacuum. Your setup is extremely unorthodox as well as the explanation. You seem to understand some of the basic principles very well and then end up accepting the flawed ported vacuum tune..... 🤷🏻
@trailerparkcryptoking5213 Manifold vacuum works nice for some setups, usually with small cams and for people that don’t know how to recurve a distributor to get the base timing that they want. But if you think it makes a drastic difference otherwise you’re fooling yourself. I bet you think engines need a little back pressure too!
Use what you engine prefers. My Cadillac, ported vacuum as the Buick with a low performance engine or standard engines runs great. My Cleveland 351 runs 100% better with manifold vacuum at 36 degrees at idle. My worked 351 Cleveland with 5" vacuum runs no vacuum and is locked out at 40 degrees, still experimenting though!. Might add ported and see what it does for cruising. So it depends on the motor, cam etc.
Or you just buy progression ignition and tune the entire timing curve of the engine. I’m thinking about purchasing one but I’m still on the fence spending so much money on all other aspects LOL
There is no reason to even comment on here...most people just dont get it...all my cars run excellent running ported vaccum aka timed vaccum! to the distributor can... Locking out or manifold vaccum is a race only thing...and yes you can use manifold vaccum if you wish on the street as long as you have mechanical timing working and you have tuned your engine accordingly IE total timing all in by the required rpm of your engine application.. But full lock out is not for the street or cruising fouled plugs will be the result.... And no any electronic style timing devices just add complexity to the system and are best left for racing or modern OEM use as when they fail you will not be able to just fix it on the road..as you can with an analog system weather points or magnetic pick up...and lastly the proof is in the fact that all my cars run well and even my 87 ramcharger roller 318 4bbl gets 15mpg... At 5800lbs curb weight 4x4.....So I know how to tune my vehicles! 😂😂😂... And in the end thats what matters!
Set your base timing with the manifold vacuum hose disconnected. That will give you the very base timing. It might be 4, 6 or 8 degrees or whatever, then when you connect the hose back to manifold vacuum that will immediately add another amount of advance to the base. Say 6° initial plus 16° of vacuum, that would give you 22° at idle. That will make it idle fast, so you can reduce your throttle setting a little to slow the engine back down.
Good video. One of the better ones I've seen on the subject. I ran a scanner on my 2011 truck and noticed that the computers ignition timing was at 31 deg. advanced when idling. Just like if the vacuum advance canister was hooked to manifold vacuum, if it had one.I agree that the difference is at idle. At a certain point off idle, ported and manifold have the same vacuum. The vacuum canister on my car doesn't start advancing the timing until 7 inches of vacuum is present and maxed out timing at 16 inches. 20 degrees total advance. I also have a gm vacuum canister that is maxed out at 7 inches of vacuum. If you change your cam and that changes your manifolds vacuum, you will need to change your vacuum canister. No use having a canister that maxes out at 17 inches of vacuum when you're only making 12 because of the new cam. I've ran ported and manifold. Right now I'm running manifold. I've heard the argument that you don't want manifold vacuum because the vacuum/timing decreases when you accelerate. We'll it does but vacuum doesn't go to zero unless you floor it. Don't you want timing to decrease when the mixture in the cylinder gets more dense? Just my 2 cents
Someone that actually understands it. Ive commented on several other of these videos that ported and manifold are exactly the same, just that ported is switched anove the throttle blades. Not taking into account emissions, both can be tuned to do exactly the same thing, it just depends on how you set up your mechanical advance and initial timing. And just as you stated, connecting to manifold does make them idle better and feel snappier with no load, but put it in gear and crack the throttle and all that advance instantly dissappears until the mechanical advance starts to come in.
Very good explanation of vacuum vs ported. I was having issues with mine getting hot in stop and go traffic. After watching a lot of the videos I tried hooking to manifold vacuum. That solved my problem. I know longer get hot in traffic. I think the answer to everybody’s question is try it both ways and see what works best for you. Also I gained 2 to 3 mpg on the hwy. city driving still sucks. Lol
You are absolutely right in what you say. Have also wondered why some "experts" think you should have vaccum advance all the time. If the engine needs more ignition at idle, the mechanical setting changes instead. The last thing you mention is also very important on an engine with a hot cam, idling will be even worse if the ignition also starts and "rocks" as well
Great Video, Makes great sense. So basically those that enjoy the Manifold port are enjoying the better Idle Quality because of the added timing by the can. But they sacrifice the loss of timing at the point the throttle is cracked open. If you chose to use port, you can still benefit from a Nice Idle quality by setting your mechanical advance to more (preferably using a vac gauge to monitor max vac signal). I'll continue with the port setup but dial my mechanical to what the engine likes with the gauge for a smooth idle. My plugs look rich, so I think Ill try going from 12° to 14° or more if required, we'll see.
There is a myriad of variables as to which vac take off is more suitable and it is always combination specific.
As a general rule I prefer ported vacuum but I always test straight vacuum aswell.
Whatever the particular combo works best with, is absolutely the right way to have it set up 👍
Also when you close the throttle at high rpms, the ported signal will be zero. I've tried it both ways and my motor runs noticeable cooler with manifold vacuum. Probably less chance of burning an exhaust valve too.
Well if you want vacuum advance at idle because of a larger cam then you need manifold vacuum. Some set-ups do better on manifold. So it just depends on the amount of timing and where the engine wants it.
Depends on which vacuum canister is installed on your distributor. They switched to ported vacuum for smog engines to make the exhaust manifolds run hotter.
A canister calibrated for manifold vacuum is all-in with just a few inches of vacuum whereas a ported canister requires more vacuum, usually 7inches or more.
If you connect a ported canister to manifold vacuum, timing drops out with throttle tip-in.
My 75 Lincoln with 460 was not happy until I dialed in 38deg with manifold vac at idle. This new ethanol fuel burns different than the old stuff. It also doesn't help my engine is probobly 7-1 compression with zero quench (thank you malaise era engineering). Maybe my damper has shifted but that's the number where it finally idled good.
Big bore engines like a lot of timing at idle...you did the right thing! Manifold!
I think most of these guys try to avoid properly curving a distributor by hooking the vacuum advance up to manifold. My 8.1:1 440 in my 4700lb 1986 Dodge 4x4 Ramcharger has 20* initial, 38* mechanical total, and 18* ported vacuum for a total of 56* at cruise. At Idle, it pulls 19" of vacuum, tested with 3 different gauges. I built it for low and mid range torque, cruise @ 60mph is 2,100rpm. I get 19 mpg. Instant throttle response with a Thermoquad from idle through any part of the rpm range. No pings on 87 E10. With a 1200 stall converter that actually stalls at 1400, I whack the gas and it JUMPS.
Either will work, the initial will alter with each. The total will be the same when the optimum is reached for your combination.
Question…. Any troubleshooting tips you could give me on why I’m getting 15-20 lbs of vacuum at idle on my ported port? When I try an take it to square with my idle screw it just kills engine. My timing is maxed also due to detonation. Timing 12-33
Throttle blades are open too far - what kind of carburetor are you using? What do you have for a cam, and is it 12 degrees with the vacuum advance plugged in or without?
@ summit 600… cam is part of the eldebrock performer package. Yes 12 degrees initial without vacuum advance. I’m not using vacuum advance at all by that’s not relevant at this point. Just answering you! Thanks for helping
@ 2172 cam to be exact
@ totally wasted your time…. Sorry. I was hooked up to wrong port. Definitely learned something today though. Again, thank you
No problem, for that combination manifold vacuum might work better for you. It will probably like the additional timing at idle. Good luck!
Ported vacuum is NOT manifold above the throttle blades. Manifold vacuum is created by the pistons displacing air. Ported is created by the Venturi effect of air flowing past that port above the throttle blades.
There is no debate amongst those who understand the difference. For street/strip applications you use manifold vacuum for your advance. Ported is for emission controled vehicles. End of story.
"really smart people talk about this topic that don't understand how this functions"
The video is aimed exactly at people like you. What you’re describing is the venturi signal that activates the vacuum secondaries on a Holley style carburetor. You do not understand how it works and should watch the video again. Your incorrect explanation is exactly why people seem to think ported vs manifold vacuum will affect anything but their timing at idle. I’m sure you do too.
Buy a timing light and check for yourself, but prepare to be upset by the reality.
@@426440yes, just like how a vacuum secondary works, and like how a fuel metering circuit. The Bernoulli's principal. That port in the throttle bore is situated where it is for a reason. And it's not to expose it to manifold vacuum. It's where air velocity is high between it and the throttle blades. But unlike a fuel metering circuit or vac secondary the signal diminishes once the throttle blade moves past it. But you believe what you want, bro.
It’s not about believing what I want, it’s knowing how it works. The signal doesn’t diminish as you open the throttle blade, it matches the manifold vacuum signal. I demonstrate this in the video.
The irony is that it’s YOU believing what you want, when it’s clear you’ve never actually checked how these function. But keep believing that switching from one to the other is changing your timing curve at anything other than idle. It doesn’t actually matter, because both will provide the same vacuum and additional advance at WOT, zero. And they will match at part throttle and every other non-idle condition.
I understand how you are explaining you think it works, but there is a reason that the signal for the vacuum secondary canister on a Holley style carb is at the top of the venturi (like a booster is), and there is also a reason it protrudes into the venturi and is shaped like it is.
@@426440 how the vacuum is created is bit of a moot point. The more important point to make is, you do not use ported vacuum on a vacuum advance for street applications. It does not apply timing advance at idle when it needs it. High vacuum = need more advance. Ported was an emissions era strategy and nothing more. Would highly recommend finding the article by John Hinckley "Timing and Vacuum Advance 101".
Hi there I looked into this topic a lot, my original 350 which I tune on ported which I like it this way, but originally it came on full vacuum I did not give a chance to tune on it, I have full stock setup , what you think?
Manifold vacuum only! Set your initial timing on about 15 if you have an HEI which will give you 34-35* total. Get a spring kit and use whatever springs give you all in centrifugal timing by 2500 rpm. Make sure your distributor is in phase also. Best to use an aftermarket vacuum canister and adjust the stroke to give a good 15* of advance under full manifold vacuum and adjust the rate spring as aggressive as you can without any audible detonation! If you have a factory HEI the modules crap out around 5000 rpm so if you rev higher get a good aftermarket ignition module! When you get your ignition setup properly then tune the idle mixture and curb idle on the card and when you get it right, the engine will be extremely responsive....
Well 3248 people have witnessed your improper tuning technique! Take a look around on TH-cam....there are expert performance guys with decades long resumes that will tell you “manifold” vacuum. Your setup is extremely unorthodox as well as the explanation. You seem to understand some of the basic principles very well and then end up accepting the flawed ported vacuum tune..... 🤷🏻
What is the base timing set at without the vacuum plugged in?
@@426440 14 degree
@trailerparkcryptoking5213 Manifold vacuum works nice for some setups, usually with small cams and for people that don’t know how to recurve a distributor to get the base timing that they want.
But if you think it makes a drastic difference otherwise you’re fooling yourself. I bet you think engines need a little back pressure too!
Use what you engine prefers. My Cadillac, ported vacuum as the Buick with a low performance engine or standard engines runs great. My Cleveland 351 runs 100% better with manifold vacuum at 36 degrees at idle. My worked 351 Cleveland with 5" vacuum runs no vacuum and is locked out at 40 degrees, still experimenting though!. Might add ported and see what it does for cruising. So it depends on the motor, cam etc.
If you have to go through emissions use ported vacuum and if you're going to race used manifold
Or you just buy progression ignition and tune the entire timing curve of the engine. I’m thinking about purchasing one but I’m still on the fence spending so much money on all other aspects LOL
There is no reason to even comment on here...most people just dont get it...all my cars run excellent running ported vaccum aka timed vaccum! to the distributor can... Locking out or manifold vaccum is a race only thing...and yes you can use manifold vaccum if you wish on the street as long as you have mechanical timing working and you have tuned your engine accordingly IE total timing all in by the required rpm of your engine application.. But full lock out is not for the street or cruising fouled plugs will be the result.... And no any electronic style timing devices just add complexity to the system and are best left for racing or modern OEM use as when they fail you will not be able to just fix it on the road..as you can with an analog system weather points or magnetic pick up...and lastly the proof is in the fact that all my cars run well and even my 87 ramcharger roller 318 4bbl gets 15mpg... At 5800lbs curb weight 4x4.....So I know how to tune my vehicles! 😂😂😂... And in the end thats what matters!
OK. So with all this debate. No one has stated how to set your base timing with the advance connected to manifold vacuum or disconnected. ??????
Set your base timing with the manifold vacuum hose disconnected. That will give you the very base timing. It might be 4, 6 or 8 degrees or whatever, then when you connect the hose back to manifold vacuum that will immediately add another amount of advance to the base. Say 6° initial plus 16° of vacuum, that would give you 22° at idle. That will make it idle fast, so you can reduce your throttle setting a little to slow the engine back down.
Manifold vac