Guys, can someone tell me why I saw so many cars at a local show that were not using their vacuum advance canisters on their distributors. The only connecting hoses to Edelbrocks were fuel and PVC connections but vacuum ports were plugged. I thought the vacuum advance connection was needed to pass emissions. (CO @ load) Please inform!

Hhhmm....I've heard the vacuum cannister is for fuel economy??

But to answer your question....well my guess would be (1) our old beloved classics don't need to pass emissions and (2) it probably makes for a cleaner engine compartment to eliminate one hose that's not extremely critical.

Aside from that, my only other guess is because people all too often try and imitate true race cars, hence why people put big rear tires/skinny front tires and big lumpy camshafts in their street car.

because people don't understand the benefits of using the vacuum advance. all they know is that the cars at the racetrack don't use it, so they don't need it.
personally, i think it looks liek crap when that vacuum can just hangs out there doing nothing. it just looks kind of "hacked' to me, and i will notice that on an otherwise beautiful car.
then again, my tastes go toward the functional side of things..

It will keep your plugs from fouling while idling and tooling around town in third or fourth gear. The thing only comes in play when you are making Vacuum; at full tilt the initial and centrifugal provide the entire advance. The initial and vacuum advance changes the curve at lower engine speeds.

I agree that its mostly based on the mentality that "race cars dont need em, and I race my car, so I dont need one". Im not sure if people think they just dont need them, or if some people actually think it hinders performance in some way or what. Im not really sure why some guys dont use them(in a real street car that is).

As far as wide open throttle performance goes, vacuum advance does nothing. At full throttle, their is virtually no vacuum signal to operate the vacuum advance...thats why it does nothing at WOT. Thats also why strictly race cars dont use em. A purpose built bracket car is going to spend most of its life at full throttle, and that means no vacuum, so no reason for vac advance in a race car if it aint gonna do nothing.

On a street car though, even if it is a hardcore street/strip car thats raced a lot, its not full throttle racing all the time if its street driven. A properly set up vac advance will do good things for you during normal driving on the street. And of course, once you nail it, no vacuum will be present and the vac advance just wont do anything at this time.......so, whether its hooked up or not, it wont harm you while racing cause it wont be working. It will only help while cruising.

actually it depends on the vacuum sorce, you can hook it to vacuum so it only comes on when opening the throttle. i believe it is called ported vacuum. also a lot of oval racers around here set up there timing at a certain rpm range that they will be running at hence not using the vacuum advance.

Yes, but even a ported source has no reading at wide open throttle. As far as the two different vacuum sources, manifold and ported, they do work opposite of each other during regular driving, but neither will have much of any reading at WOT.

At idle and during light throttle cruising, manifold vacuum will be high cause the throttle blades are not open to any great extent, so all the vacuum the engine makes registers in the manifold. Thats why manifold vac would be high in this situation. During light acceleration and moderate load, you can expect the throttle to be cracked a little. Enough to still create a vacuum, but being that the carb is opened up a bit, a lot of that vacuum now registers in the carb(and through a ported source). Manifold vac goes down at this point.

So you can generally say, when manifold reads strong, ported will show a weak signal and vice versa, but neither do anything at WOT.

If you have enough vacuum present in either source to pull enough vacuum to successfully run a vac advance at WOT, than something is wrong.

With a large or semi large cam that makes very little vacuum at idle it will mess with the vacuum advance, tries to advance and it can't making the idle go up and down. If you get the right cannister as mentioned above you can fix the problem, but if you don't drive it much, its easier/cheaper just to disconnect it.

I forgot about that part Bob. Its true, some of your engines that are more on the "wild side" will be a little too radical to produce enough vacuum to accurately run a vac advance right. It takes a different cam thats capable of working with low vaccum readings in a situation like this. So, this is another reason why some guys dont use vac advance.

But you still see a lot of guys that dont run em just cause they dont want too, even if they would be perfectly capable of using one, and I dont know why many people dont use em.

Maybe most are running mechanical advance???

Most likely the clowns do not know how it works so they leave it disconnected.

I just installed the Crane adjustable canister. I almost have it dialed in, it was giving to much advance, I backed off 8 turns from max.

Most likely the clowns do not know how it works so they leave it disconnected.

Little strong aint it clown? errr vrooom3440, or whatever the heck your name is :rolleyes: you have no idea why its disconnected, and several reasons have been stated above, if it runs best disconnected, thats the way it will be until they figure it out, right?

Most likely the clowns do not know how it works so they leave it disconnected.

First off,there is no difference between ported vacuum and manifold vacuum once the throttle plates are open.
Manifold vacuum is usually used for the increased advance to "clean up" a radical idle.

And,for the record I do not run vacuum advance on my car..all my timing is "in" by 2500...I don't want or need extra timing from the vacuum advance at part throttle with my compression.

There are exceptions to every rule... specifically there are some folks, more in this forum than in the general population, that really *do* know how engines work. But there are a lot more out there that do not. When dealing with a classic muscle car it seems just a bit silly to me to have no idea what is going on up front. Thus the "clowns". I actually had considered stonger terms and decided against it :-)

Everything I have read, and it makes sense, indicates that ignition timing is dependent on flame front propagation and that the speed this happens is proportional to cylinder pressure. Thus at low pressure, another way to say high vacuum, it takes more time for the burn so the ignition needs to happen sooner. So you have a vacuum advance to accomplish this. It is a load-sensing feedback system to adjust ignition.

This is a basic physical property and I do not see why it would be different for any engine setup under *street* use (and most of these show cars were driven to the show, right?). But as always I will listen to reasonable explanations why I am wrong.

Personally I run a moderate ~10:1 compression 402 with aluminum heads and a Crane HR296. It has been a "learning experience" to get the combination to run more cleanly with the Edelbrock Performer carb I have. I do run the vacuum advance off the ported source with ~14 degrees initial. I have learned that vacuum advance at idle is too much and leads to dieseling on shutdown. I have learned to adjust the carb idle to go just under the ported position and avoid vacuum advance at idle. With my setup I have achieved up to 12 MPG on the highway with no pinging (we won't talk about my city MPG because my foot is too heavy). Apparently I am right on the edge as the other day I tried a fillup with 89 octane instead of my usual 91 octane. And it started dieseling on shutdown :-( A bottle of octane booster smoothed it out and now I know I need to just stick with the 91.

And FWIW the name is Steve, I just use the vrooom3440 monicker as I started it several years ago on another forum and have continued it to be consistent across each forum I participate in.

I see what your sayin Steve, but the reason some are taking offense is because for as many guys who dont understand ignition advance(Vacuum and mechanical), there are plenty that do. And, plenty have good reasons not to run vac advance. Not because they dont know better or because they assume its no good for a fast car, but because it actually doesnt work in every situation and lots of guys know this, and they know why it doesnt work for them.

I will agree that most often, when it comes to ignition timing in general, I see more guys locally that dont know how it works all together. You see guys with locked out timing curves and no vac advance that dont know why its that way. They do it cause either someone with a fast car told them to, or they saw a guy with a fast car doing this and they figure its right for their car. Of course, many people do know what they are talkin about though.

Just like the case of mr 4 speed. He already seems to have a pretty agressive mechanical advance curve. With that much timing on tap at an early rpm, vac advance could easily put it over the edge during cruising. And you might think, why not retard the timing and use a vac advance to get the same results at idle, still good cruise manners and maybe even take some heat off the starter. Well, like Bob said earlier, if the cams big enough and idle vac is low enough, you will have problems with the vac advance operating properly at idle. Even with one of the cans that read to a lower vacuum reading, they can still have problems keeping up right if the engines ratty enough. If thats the case, you might as well just run a real short advance curve with lots of timing real quick, or just lock it out.....there are engines that can utilize such a setup.

Like I said at first, I do agree that lots of times vac advance could be used, and its uncommon that the owner of the vehicle doesnt realize the benefits for his particular application. But, we all have to be careful not to stereotype cause every application is different and plenty of people in the know will do things a particular way because it honestly does, or does not work....some times vac advance just wont do the trick.

Even I stereotyped the typical guy in my first post. I didnt mean to, but my reply was based on MY definition of a street car(which can easily differ from the others), so I apologize for that and I meant no offense. My definition of a street car for myself usually isnt so radical by any means that vac advance cant be utilized in a good way, so thats where my line of thinking was at.