Vacuum Advance - Ported vs Manifold: Which to Use & When !!!

how since everyone's gonna say why don't you ever do a poll in the trunk I guess we'll do one today [Music] [Music] howdy and welcome to the channel today I'm Luke Thunderhead 29 here on YouTube now in this video today we're going to look at something that's a very touchy subject for a lot of folks ported versus manifold vacuum and some of the methodology behind I guess setting up your ignition timing with both of those items so I run a little Facebook page where we do a lot of how-to and tech questions and the biggest thing that I see that's misunderstood on these old-school engines is ignition timing now and a lot of folks spend a lot of time putting all these extra parts you know hi left cams they spend a lot of money to make a performance engine and then they just take all that and throw that out the window because their ignition timing is not set up you know in any way shape or form correct and they're just leaving tons and tons of power on the table so today we're just going to touch on this ported versus manifold vacuum piece and I guess let's jump right in so put on your big-boy pants today we're probably gonna hurt some feelings all right so to fully grasp what I'm trying to tell you today you need to have a very basic understanding of what folks are referring to when they say ported or manifold vacuum and what this correlates to is the vacuum port on the carburetor that is then hooked to the vacuum advanced canister on your distributor now here for example we have a hei style / Tronics igniter 3 unit that is a pretty respectable distributor and then we have a vacuum pump for bleeding brakes hooked to it to simulate our vacuum signal from our engine so the only difference between ported and manifold vacuum is it idle you're not adding any ignition timing if you're on your ported port now your manifold vacuum port is exactly what it says it is it's full manifold vacuum so I got the engine idling here in the old f100 this gauge here is hooked to full manifold vacuum you can see that it responds to any blip of the throttle this port down here is ported vacuum and if you have your carburetor set up correctly you should not see any vacuum on this port and so you know I talk a lot about transfer slots and everything and we won't get into that today but I have a little high idle switch here just to demonstrate so as you can see if we just slightly open up our throttle we start to have vacuum on our port now if we open our throttle a little bit more you'll see the ported vacuum and manifold vacuum are exactly the same and again I'm going to shut this off and you can watch our vacuum here you see how that drops to zero and again this is teed into our ported port all right I can really accentuate this pretty well on the interstate here so as I work the throttle back and forth see my foot our vacuum signal is gonna change I completely let off manifold goes high for two gunmen zero when you're into the throttle again they're exactly the same again the only difference between forwarded and manifold vacuum is that one does not add ignition timing at idle and you can just see by the vacuum signal they're exactly the same unless you let off the throttle other than that they're doing the exact same thing so vacuum advance only adds ignition timing when you're at a high enough vacuum scenario so we're gonna test out here you can actually see the mechanism move on this patron acute it when we get to a certain vacuum so let's see here because I'm not sure so it looks like about eight inches here it starts to move and we'll see when it gets too full advanced somewhere down around twelve inches of vacuum there she is at full advance and as we go up we're not adding anything else so let's drop her back down again you can see the lever arm move it looks like about five six or so we're starting to add timing so the purpose of vacuum advanced is to add ignition timing when you're at high vacuum scenarios when are you in these scenarios so jumping under the hood here you're in these scenarios when you're cruising around the road so this brings us to the question of why we need more timing when we're cruising when we have high manifold vacuum we don't have a lot of throttle input and it's really conceptually pretty simple here basically when you don't have a lot of throttle input you're not volumetrically filling your cylinder quite as much and so that less dense fuel and air charge has a lot longer burn time and in order to burn that at the proper point in the stroke where we're getting the most effective use of our cylinder stroke we have to fire that mixture a little bit sooner so that the flame propagation is at the right time so I know that's a little confusing we're going to demonstrate that with a compression tester so I've already spun the engine over with our throttle closed here I'll get another spin just so you can see you can see as you can see there we're about at 120 psi on our cylinder 1 all right so the only thing we've done here is we've wired our throttle completely open there and this would be a very low vacuum scenario with a high throttle input and we'll watch as I roll the engine over remember it was at 120 before and it's going to increase [Music] all right so she went from 120 to about 140 and this is just you know spinning the engine over very slowly so obviously you can see here with more throttle input you have more cylinder pressure and this is obviously much more accentuated when you're at a running RPM but again as you saw earlier in the video when you step into the throttle and manifold vacuum drops out like the scenario you would have here you also lose your vacuum advance entirely there's no vacuum to open that diaphragm and so again you're just on your mechanical timing all right so with all that in mind that brings us to our question of ported versus manifold vacuum finally now remember this is only adding ignition timing when your a light throttle scenarios as you've seen throughout the video and the only difference between ported and manifold itself is that manifold adds timing at idle while ported does not if you have your carburetor setup right and not too much throttle exposure so which one should you use where should you hook your vacuum line for your vacuum advanced canister on to your carburetor ported or manifold and to clear up one more misconception about all this a lot of folks will move their vacuum line from ported to manifold manifold deported and say well it runs better either way no if you go to ported you have to realize for manifold you took ignition timing and took it away until you have enough throttle input so what you have to do is advance your initial mechanical timing so I'm going to tell you the way I set up most street engines and then you can make whatever assessment you want to make and ultimately it's your choice what you choose to use now personally I've found that most all street engines that have mild cams or stock cams work the best on ported vacuum they don't require a whole lot of ignition timing at idle because the dynamics of the camshaft is just making really good cylinder pressures at idle versus a high lift cam with a lot of overlap doesn't have as much cylinder pressure at idle and requires more initial advance so if you try and run manifold vacuum on a mild cam or stock style engine what you're going to have happen is you'll have so much ignition timing being added in from that vacuum advanced canister in order for your carburetor to idle at the you know an ideal rpm you have to close your throttle way too much on your carburetor or you need to have way too little initial mechanical advance and when you step on the throttle hard and you take that timing and throw it out the window you know you're just your engine responds very lazily off the line because now you don't have enough ignition timing so with ported you can mitigate a lot of those issues now of course there is a dynamic relationship between your ignition timing and the functionality of your carburetor at idle so again remember ported we need to add a little bit more initial mechanical timing what you're looking for on your carburetor settings is a throttle position in between the point of where your transfer slots are exposed so you have a little bit of vacuum signal on those but not so far that you get to the point where if you see this little in the center of the screen that is actually your ported port for your vacuum advance if you get too much throttle exposure in you're seeing vacuum on that port at idle then you have too much throttle exposure and you need to increase your initial mechanical timing now if you go too far like I said which most folks can easily do with full manifold vacuum you'll see that now no transfer slots are exposed and the purpose of those transfer slots in conjunction with your accelerator pump is to handle the transition from idle to your main jet circuit so they work a lot better if they have a little bit of vacuum signal because fuel is already flowing and then when you hit the throttle you know it just continues to draw more from that circuit if you have no exposure at idle basically you have a flat spot between the time it takes from fuel to get going on that circuit before it gets to the engine so that's kind of the form and function of how all this works in a Holley and Edelbrock are actually exactly the same in this regard the ported port obviously on Edelbrock being up here because it's above the throttle blades in the same way it also has transfer slots so you can set everything up with the same mentality between the both carburetor styles there's really no difference now I also want to make it clear that ported vacuum is not the end-all be-all there's compromises you have to make with ported vacuum also you know even though you've advanced your initial mechanical timing relatively to an idle your advanced is still a little late and it's going to favor a richer idle mixture so you know again there's compromise you have to make on both sides I'm not really in love with either of them but for street engines I've seen that ported vacuum works really well now I'm really not a huge fan of all these compromises you have to make with these old-school engines with ignition timing they're just inherent in the overall design of a distributor you know the limitations that are associated with weights and Springs and stop bushings and vacuum advance and everything it's pretty good but it's not completely perfect and I bumped into a guy about four weeks ago that shared the same opinion and he told me he was so frustrated with it he went out and just designed his own distributor so Ted with progression ignition it's a company it just got started and basically you take all of those limitations that are inherent in the design of an old-school distributor and throw it right out the window there's just so much capability in this little package and before you run out and pay all the money for an MSD distributor I strongly encourage you to check out his website mol roll clips on a few of his videos the overview his product but it's just the coolest thing that I've seen since the advent of the t5 swap and these old Fords so with that I'll do it for me today guys we'll catch you later [Music] [Music] [Music] you you [Music] [Music] [Music] you [Music]

Channel: ThunderHead289

Views: 258,647

Keywords: junkyard digs, thunderhead289, vacuum advance, ported vacuum, manifold vacuum, do i need vacuum advance, adjustable vacuum advance cannister, should i run manifold vacuum, should i run ported vacuum, ported or manifold vacuum

Id: WD_bhDq_8tY

Length: 15min 30sec (930 seconds)

Published: Mon Apr 13 2020