The Vacuum Advance Debate!

so the video we did yesterday about vacuum tuning we're tuning with the vacuum gauge I brought up the point about vacuum advance should always be hooked supported rather than manifold vacuum and naturally it spurred a little bit of a debate and maybe I should clarify that and make an obvious my reasoning for this with a demonstration so we set up our vacuum hose thing again but before we do that let's clarify some terms first things first is that vacuum advance has nothing to do with performance if you're focusing on only the performance aspects of your car leave it off leave the vacuum line off or don't you know don't put a distributor in it that has vacuum advance the pipe performance of race distributors have no vacuum advance real race distributors are completely locked out there's no advance at all street strip distributors will have some mechanical advance but it's usually limited to like 10 to 15 degrees and only to make it easy to start the car when it's hot but for performance purposes no vacuum advance the purpose of ignite in advance but what it does is it aids in part throttle light load fuel economy and drivability so what we're going to do here is I'm going to show you on this distributor stock distributor oh it's got a pre-trial X on it but it's it's otherwise the stock distributor with stock you vacuum advanced canister I'm going to show you the difference between ported and manifold and then you can make up your own mind on which works better now keep in mind this port adore manifold they'll function pretty much exactly the same as intended out on a highway let's say backing off the throttle they'll bring all of the timing in and and they'll function pretty much the same it's your wolf Idol or breakaway performance where the differences so right now I've got the vacuum line here hooked to manifold vacuum to the manifold vacuum port on the carburetor let's take this thing for a ride and I'll show you what goes on okay so as I said it took to manifold right now maybe as soon as we started it it's getting vacuumed right now pop the value line it off and you can see the difference of motion okay now watch what happens when we we pull away now this is going to be like on a typical it's a traffic situation or let's say pulling onto an on-ramp you know when when you're part throttle performance is important now what it's it's got all of its advance dialed in right now but watch what we accelerate the very first thing it does as soon as you touch the gas is back off the timing its retarding the timing when your engine needs it the most here watch again and that was a back off on the throttle now it advances okay so now I'm going to turn around well let me let me switch the lines she'll ask me to do this okay so now it's looked supported and let's see we're gonna pop the vacuum line off and it doesn't move alright so right now we're idling only on our initial advance [Music] white bottle in advance this up a little bit [Music] we lose here let me drive through the pavement is solid okay so now we're gonna accelerate the same way now watch remember there's no advance in it right now it's not moving okay so right now the engine is getting fully advanced and as we back them off the throttle it starts to bring in the advance so basically what's happening is hooked to manifold vacuum the distributor is doing the exact opposite of what you wanted to do for performance it's taking the initial it's taking the initial timing plus the vacuum timing that's dialed in as soon as you start the engine and it's removing it as soon as you hit the throttle when you've got a supported vacuum when you hit the throttle and accelerate it's got full the timing that you put in and then as you come off the throttle it'll advance and give you that part throttle economy and drivability that's it in a nutshell there's plenty in debates I know I went I read guys on the comments left links for people writing treatises on why it's gotta be manifold valium or why is it reporter vacuum but there it is there's the demonstration when it's hooked to manifold vacuum it works opposite of how you want your ignition advances to work once hook deported it works for that specifically for that part throttle drivability that's it hope you got something out of that I see you tomorrow

Channel: Uncle Tony's Garage

Views: 125,100

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Id: r7ggHhdujj0

Length: 6min 25sec (385 seconds)

Published: Wed Jun 17 2020