How To Choose Between Timed or Manifold Vacuum

today we're going to talk about something a little controversial in timed vacuum versus manifold vacuum when should you use either one and then should you just get rid of all of them and go right with a race style setup with a locked out distributor so let's talk about it so let's first talk about timing in general there's engine timing and there's ignition timing they both work off the same principle the rotation of the crankshaft and where the crank is in relationship to where the piston is so it knows when to fire the spark plug to fire or burn the fuel and air mixture that's in the cylinder but we have to look at also too do we need to advance the timing or the timing depending on how much load is on the engine and that's we're going to talk about specifically today is when do you advance the timing in the engine and how do you reference the right port on the carburetor or throttle body to get it to fire at the time that you want to to fire and that's the controversy there is which port to use so we're gonna talk a little bit about both and then we're gonna give i'll give you my example or tell you what i go to really to use first on all these now why should you run a vacuum advance in a street car and that's we're gonna concentrate on today is more street type applications but we're going to cross over a little bit with a locked out distributor and talk a little bit about that as well but vacuum timing is very useful to use on a street engine to get to where you want the timing set depending on the load of the engine and the rpm of it so when you use a vacuum advance type of distributor or ignition timing on a street car you get a little better starting you get better cold starting your driving uh style gets a little bit easier because you're not uh you're pulling timing as the engine is demanding it or giving it timing depending on where you're at in the in the rpm range in the load range your off vital characteristics are typically better with a vacuum advanced distributor on a street car because you're operating in a lot of different things your stop stops sitting at a stop light you know the advances out of the engine you're back at 20 degrees of timing wherever you have it set at and then once you get going you know the vacuum pod and the mechanical uh advance within the distributor will take over but it's getting the the relationship between the two that's critical so there's some people that say that that you have to run a vacuum style advance on a street car and i don't disagree with that for the most part but really it all depends on a couple of different things now what it boils down to is which one should you use should you use manifold vacuum or should you use timed vacuum so before we talk about what those are let's talk about the factors that will give you to figure out which one you should use so the three things you really need to concentrate on is how you plan on driving the car is it a street cruiser a little bit of street strip is it a drag race only application is it a road race car autocross car whatever the case may be knowing what the driving style is the first step in it the second is what the cam specs are the cam is going to really dictate a lot of that because it's it's where it tell everything about what's going on in the engine as far as the the valve train is concerned starts with the camshaft so you really need to understand what the specs are what the power operating range is and and what uh you know what the ratio is that you're working on it here because it's going to matter how the timing affects what the fuel in areas that's going into the cylinder and last one's compression ratio you have to really understand what the compression ratio is and what the rest of the spec of the engine is before you can really decide on which port to use whether it's timed or manifold so it's kind of basic i get to understand but we have to talk about that real quick because everything else that we're going to talk about from here on out depends on what the whole package looks like and really those three things how you're going to drive the car what the cam specs are and really what the rest of the combination is so let's talk about the three most common things at least that i deal with and maybe you are as well and that is a carburetor and a throttle body efi system and where the ports are on each now if you look at the edelbrock carburetor on the passenger side this is your timed port the one on the driver's side is your manifold vacuum on a holley carburetor you can see both of them are plugged here but the one on the side of the metering block here is the timed vacuum and this one down here in the bottom is the manifold vacuum when you look at a this throttle body efi in particular the one down here in the bottom is your manifold vacuum you can see the port that it comes out of we'll talk about that here in a quick second and then this one up top here is your timed vacuum now knowing which one is is super critical but obviously knowing where it's at on the carburetor or throttle body to hook it up properly is also key now let's talk about the differences between timed vacuum and manifold vacuum the timed vacuum port which is this one up here is the port that is above the throttle blades in the bore if you look at this edelbrock carburetor the throttle blades are down very close to the base plate of the carburetor that vacuum port is above these throttle plates same with the holley same with this fast unit all the timed ports are above timed vacuum only adds timing at part throttle or lot light throttle it does not add any timing to the distributor at at no throttle at idle it's just there's no there's no reference from it there's nothing that's pulling on everything that is above the throttle body when the blades are closed isn't drawing any vacuum it's closed so it doesn't pull any timing into the distributor when the when you're using the timed port now when you're using the the timed vacuum advance always comes in a little bit later because you do have a little bit of lag time here when you hit the throttle and the blades open up and now the the port above it is starting to read vacuum that's being pulled through the system it takes a second or two not really that long but it does have some slight hesitation and then it has to go to the distributor that the distributor has to react through the vacuum pod to advance or the timing whichever the case may be so there's always a little bit of a lag time there and the way you cure that is that the distributor but really it's just understanding that you know the the ported or the timed vacuum you know it's also what they use for the the fuel economy side or the epa side of it you know it's always used on the timed vacuum port it may be the reason why they came into play i really don't know but um you know the the differences between the two that time like i said it's just going to be a little bit you know a little bit um you know different you know like i said no no load at idle it's not going to read any vacuum now let's talk about manifold vacuum if you see on this fast throttle body this one that's down at the bottom and you can kind of see that reference hole right there that is where the manifold vacuum port is reading from it is always reading constant manifold vacuum when the engine is running what's going on in the intake manifold vacuum typically requires a little bit less mechanical advance within the distributor because you're constantly under pressure you're constantly reading what the engine vacuum is and you're you usually have a little bit more initial advance when you're running manifold vacuum the other side of that is too is you know when you've got more fuel and air going through there or you've got a lot of fuel and air going through there you need a little bit more fuel across the entire operating range when you're using the manifold vacuum it's just part of it you know you're again we're talking about the time that it takes once the fuel and air mixture gets into the engine and starts to compress and the amount of time it needs to burn when you're using manifold vacuum typically you need a little bit more fuel running through there and we'll talk about that here again in a quick second of why you'd need that but those are the main differences between the mechanical or excuse me the manifold vacuum and the timed vacuum it's just where it's drawing manifold is always below the throttle plates the time is always above the throttle plates now let's talk about which one or when you should use either one now timed vacuum is typically used on emissions controlled vehicles but literally we're not talking about any of that here but it's always used there because it's it gives you a little bit less fuel that's needed remember we just talked about the manifold vacuum requires a little bit more fuel running through the system you know through the the carburetor the throttle body it just the timed vacuum requires a little bit less on vehicles with a really mild cam or a stock cam and an automatic transition time timed vacuum is really really good it allows everything else to work you don't have a really long duration in the camshaft and when you don't have all those things you can get away with using that timed that timed vacuum now the other side of that is engine or excuse me manifold vacuum when you have an aggressive camshaft you would need to probably start tuning with manifold vacuum it's just a better way of doing it because the longer the duration and the more rpm or the more manifold pressure that you're seeing or the engine pressure that you're seeing internally requires that you have a little bit more advance a little bit quicker and a little bit more initial advance so manifold vacuum is almost always the place to start now the downside of that is is again we just talked about you're going to run a little bit more fuel when you're running manifold vacuum so you know the the it's always going to be a little bit richer your afr is going to always read a little bit richer when you're running uh manifold vacuum and the advanced through the distributor so you may be a more heavier smell of fuel at startup because you've got more fuel going through the system that's what the manifold vacuum you know side needs so just a couple of quick variations or times when you can use it but for the most part if you stick to that if you have a really aggressive camshaft on a street car go with the manifold vacuum if you have a little bit less mild i hate the term but if you use like an rv cam then great use the timed vacuum and that's where you start your tuning process with either one now let's talk about engine timing and i'm going to try to draw this out the way my high school shop teacher taught me this well quite a few years ago we won't talk about that but let's talk about the engine timing and how it relates so we can understand where the advance comes in and and the comes in the timing so let's call this top dead center up here this would be bottom dead center down here okay let's start uh with a event right here first event and then um these are crank shaft rotation around until you finally get to the final event somewhere over here okay so this first event is the intake valve opening okay it is when the intake valve opens you draw some suction from the manifold or you know the pressure that's in the cylinder from the piston drawing down so it is essentially suction i guess and then somewhere down here um you've got the intake valve closing as you rotate around here and go through more once the intake valves close then i guess this stroke here becomes the compression stroke because now both valves are closed you're compressing you're getting ready to go to the event where the plug fires and you start to uh you know get the timing that you need so let's talk about once we get past the compression ratio or the compression stroke here um ends at top dead center okay so the timing that occurs let's just draw a line straight through this all and pretend that's straight um so we're talking about degrees of timing here anything after top dead center we can look at as far as the the retarding of the timing but it's before top dead center that we need to concern ourselves with because that is where that's where the the timing event occurs so if you look at that line straight through i'm gonna try to draw that again that's a little ugly i'm not an artist i guess as you figure it out so let's look at this straight line through here that's much better top dead center bottom dead center when you look at degrees of timing of what's going on at top dead center and what's going on before that that degree of timing there can change depending on what where you're at in the in the curve so let's say when you have initial of 15 degrees of timing before top dead center let's say you set it at 15 degrees that is where the plug fires here and then it burns through and then it gets to the other side of top dead center where it ends up done being burning the fuel and air mixture and then you go into the exhaust side of it and and spitting out the uh you know the uh the exhaust after you go through the power stroke where you know you get all the the power that you're getting from burning the fuel and air and the expansion of the gas within it when you're putting more advance into it all as you're doing is putting more on this side of it so let's say all in with your mechanical advance vacuum advance everything you're at 35 degrees which is typical i mean those are pretty average that's all that means is the time before top dead center that the plug fires and gives it time to burn now why do you need more advanced why do you need more timing because you need more time remember we talked about that really at the beginning is you need a little bit of time to burn fuel and air it doesn't burn instantaneously you have to have that time in the system so when you need more time to burn it because you're under more load or more rpm that's where the timing it advances and that's what that all that means is what's going on before top dead center 15 degrees of crankshaft rotation before top dead center now let's talk about what's going on the distributor when you talk about that timed or manifold vacuum system where you're using the vacuum pod on the distributor to to control the timing so if we look down in here that vacuum pod which either goes to your timed or manifold vacuum port is connected to a little plate here when you pull suction on that it will pull this plate and twist it back that way when you do that this mechanism here that is attached to that plate is advanced you will get it earlier all of these little spikes here on the rotor or underneath here is the where the timing occurs to fire the plug when it goes past the pickup here when you advance that you move this blue little sensor over and it fires the plug sooner when you pull advance on the dis from the from the manifold it rotates the plate turns it gives you now you've seen probably on the distributors these plates here does the same thing it advances the rotor and changes the when it fires based on what's going on in the cap in which terminal to hit so we're talking about that that is what it is that advanced pod is pulling that it's rotating it and it's changing the plate on the bottom in reference to where this is spinning based on the camshaft position which is attached to the crank by a timing chain or hopefully not a gear drive so that's what's happening internally in the distributor now i want to show you this one as well because it's a little bit different setup when we talk about going with a race type setup this is more street everything here is contained the only thing you need to make this run is a coil and then obviously the spark plug wires and you're good to go this system here the timing is not controlled by vacuum of the engine or by a mechanical advance within the distributor it is controlled by the box the ignition box controls the timing now when you talk about a locked out distributor all as that means is there is none of that mechanical advance going on inside the distributor again it's all controlled by the box where it's triggered simply is picked up by that pickup and that little pole on there that tells it when it's going to fire each cylinder that's a locked out distributor means there is no mechanical advance no vacuum advance within it everything is done now this happens to be the setup for the chevelle i am going to run an ignition box and that distributor again you're going to get some people that are going to argue and say well you should always run a vacuum advance on the street and i don't disagree with that i think that's a great it's a great thing it's not a bad you know bad situation but for what i need because i want the rev limiter and i want to run a two-step with this um then i need a little bit ignition different ignition system and i prefer to run it that way with an ignition box a locked out distributor versus the mechanical advancement vacuum advance the camshaft that i'm running is not too rowdy i can run it off mechanical vacuum or excuse me manifold vacuum run that distributor and a coil and that set up and be just fine but it's preference and who knows i may go back to a vacuum advance because it's not a thousand horse street engine we're talking about a very mild 700 horse ish big block so i wanted to show you the difference between the two so it's important to understand what's going on inside the mechanical advance and the vacuum pod and what the locked out distributor looks like so where should you start with all this honestly the best place to start is always with the timed port and if you don't get the characteristics of the thing running the way you want it to it's sluggish doesn't you know throttle response isn't good then you can always switch to the manifold vacuum at a different time but again with a mild cam you know if you go straight to manifold vacuum with a a mild cam you know the throttle spot response can be a little bit more sluggish there's too much vacuum pulling on that on the distributor and giving it too much advance but the camshaft doesn't have enough you know lift and duration to to get things moving the way you need it to so you need a little bit more time and maybe the timed port's a better place to start you know again if you have a really aggressive camshaft you try to do it on the timed port then again it may be a little sluggish because it's not you're not delivering enough fuel and air in there because the cam needs more you're giving it more time to draw more fuel and air in and you need more to keep things you know making power the way you want to so it's always a give and take and that's the that's the the real challenge with it and that's where the arguments always start with this is neither one of these is perfect that set up with um you know what that i showed you a minute ago using the locked out distributor is not perfect either again everything's a little bit of a give and take you know the the ported or the timed vacuum and the manifold vacuum they both have their positives and negatives you know one's really good at one not so good at the other and vice versa so it's really kind of up to you what you decide to do but always start with the time i've always had good luck with that because even if you figure that well i i have kind of a you know a mild camshaft but it's kind of on that you know 270 280 advertised you know side and maybe i need a little bit more you know a little less initial timing in the distributor grade i'll try it on the time side start with the time you can always switch to the manifold it doesn't give you the results you're looking for so everything we've discussed in the past in regards to tuning it's a process there's never a you know bolt this carburetor on use that distributor and everything's perfect it's always a process that you have to go through you always have to go through all the steps and if that means changing and working with different ports whether it's timed or manifold whether it's changing the mechanical advance the weights the springs and the distributor to get it dialed in for your combination then those are the things that you have to do there's nothing that's perfect right out of the box you're always going to have to carburete tune you're always going to have to tune the distributor you're always going to have to work a little bit with the throttle body efi whatever it is you're always going to have to do a little bit of something with it so keep that in mind when you're working especially when you're working on the vacuum side of the carburetor or throttle body to deliver to the distributor you may have to change some things around there is no clear definition that if you're using this camshaft this compression ratio intake manifold header primary tube size and so on and so forth that here's all the settings that you use everything's different transmission is different your driving style is different the torque converter is different there are too many different variables in it so just get used to the fact that you're gonna have to do a little bit of tuning and the more you tune the better it's gonna be when you get all said and done so hopefully that gives you a little bit more understanding about what those two ports are and what they mean and when you can use them and what maybe are some little differences between the two and maybe when you can you know use one over the other but again it's just a process and don't cheat yourself through it go through it and learn with it and figure out what the engine is demanding and when you're all said and done you'll have a much better you know running engine and car so anyway if you have any questions on this don't hesitate leave them down below when we get down to doing the chevelle here in hopefully a couple of months when the things fired up i'll probably start with the that easy run distributor and then i will switch over to um you know my race set up i guess if you want to call it that with the locked out distributor and timing box to show you the different process in the tuning but those are a lot of videos down the road so we won't even think about that yet but again if you got any questions don't hesitate leave them down below love to answer them for you and we will catch you guys on the next video we'll see you

Channel: Muscle Car Solutions

Views: 63,418

Keywords: engine vacuum, tuning, timed vacuum, manifold vacuum, ported vacuum, intake manifold vacuum, carburetor vacuum, intake vacuum, constant vacuum, timing vacuum, distributor vacuum, vacuum pod, timing advance, engine advance, engine tuning, edelbrock vacuum ports, holley vacuum ports, EFI vacuum ports, throttle body vacuum, engine timing, mechanical advance

Id: Kw05YQK11YE

Length: 23min 56sec (1436 seconds)

Published: Sat Oct 24 2020