barnett468

Unfortunately, that article has several inaccuracies and does not contain enough information, therefore it is misleading and it has caused myself and others countless hours explaining to others why it is a bad idea to simply plug a vacuum advance into manifold vacuum . . Also, due to the type of inaccuracies and omissions it has, it strongly suggests that the "author" was no more of an automotive engineer than Winnie The Pooh is and it suggests that the "author" simply made up a title for himself in an attempt to reinforce the validity of his claims.


Below are a few, simple, no brainer guidelines to use:

1. Never just shove a "high performance" distributor in and set the initial timing and think its good because in fact it may cause your car to run slower than the one you just took out.

2. Never bolt on a carb and think it will magically be perfectly jetted for your car because it won't be.

3. Never plug your vacuum advance into ported vacuum unless you test its effect in a scientific way AFTER all other tuning is done because in some cases, it will reduce performance.


WRONG

“Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing... ...throttle response…”

RIGHT

vacuum advance does not function under hard acceleration because the engine vacuum drops below to point at which the vacuum advance begins to work, therefore, it has no affect on acceleration...none, 0, zip.


WRONG

“After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark"...”

RIGHT

Just what century is he talking about because as you can see by the diagram below of a 1955 car from a factory gm service manual, the vacuum advance is clearly connected to ported vacuum and there were no emissions standards in 1955…none, 0 zip.


WRONG

“If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle…”

RIGHT

This guy can’t even add . . most of the 50’s, 60’s and early70’s cars that used ported vacuum used a minimum of 6 degrees btdc at idle and many used more including the 1955 365 hp corvette and the 1965 ford 6 cylinder with automatic transmission of which both had around 10 so even at the minimum advance of 6 degrees btdc, 6 plus 34 is 40 . . always has been and my guess is that it always will be . . also, he is not adding the advance from the vacuum advance.


This is not only absolutely positively WRONG . . It is irresponsible and potentially hazardous to an engine.

“For peak engine performance, drivability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.”



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jwog666

ok i guess my dyno tuning results on my small block powered buick were wrong then, carry on
here is another article http://www.gofastforless.com/ignition/advance.htm
" The mechanical advance is adjusted for high load WOT conditions. Under light load, part throttle conditions the manifold pressure is lower so volumetric efficiency is lower so the cylinder pressure is lower so the fuel mixture burns more slowly. This means you need to light the mixture sooner so you reach peak cylinder pressure at the ideal time. This is the purpose of the vacuum advance. The lower the load is the more it will advance the timing. Vacuum advance will improve gas mileage and drivability of a street driven car. A lot of guys think a vacuum advance hurts performance, this is not true. The vacuum advance is entirely independent of the mechanical advance. They are two separate systems that perform two separate functions. The mechanical adjust timing based on RPM where the vacuum adjusts timing based on load. Under high load, WOT, performance conditions there is almost no manifold vacuum so the vacuum advance does nothing. The only time the vacuum advance adds timing is at part throttle, low load conditions when there is manifold vacuum. So unless you race at half throttle a vacuum advance will have no effect on performance. It will however improve part throttle drivability so unless your car is a 100% race car I would recommend running a vacuum advance.

You're probably thinking, "Sure there is no manifold vacuum at WOT but aren't I supposed to use ported vacuum for the vacuum advance." Hold onto your hat, THEY ARE THE SAME THING! Except ported is shut off at idle. There are a lot of misconceptions when it comes to the ported vacuum source. After hearing 20 different theories I decided to hook up two vacuum gauges, one to manifold and one to ported, then drive my car and watch it. I found out they are the same, except the ported is shut off when the throttle is closed. Even then I had a hard time convincing guys so I hooked up a couple MAP sensors and a throttle position sensor to a data logger and recorded them while driving then dumped it into a spreadsheet and made a chart. As you can see, there is a direct relationship between throttle position and vacuum. When the throttle is closed vacuum is high, when the throttle is open vacuum is low, and ported vacuum is the same as manifold except when the throttle is closed. So which one do you want to hook it to? I prefer manifold vacuum. This pulls in more timing at idle which is good since there is virtually no load. Your motor will idle smoother and cooler with the extra timing. One night I was at the drags and my car was running hot in the staging lanes, I swapped the vacuum advance from ported to manifold then it would idle all night at 175°. Believe it or not the purpose of ported vacuum is to raise the temperature at idle, to lower NOx emissions. If you're like most hotrodders that is of no concern to you. If you have a big cam with a choppy idle then a vacuum advance hooked to manifold vacuum can really help. It will idle smoother and requires less throttle to maintain speed. Often a big cam requires you to open the throttle so far that the curb idle adjustment needles won't work. Hooking the vacuum advance to manifold vacuum will allow you to close the throttle some which may be enough for the idle mixture screws to work. Someone told me he noticed less dynamic braking with the vacuum advance hooked to manifold. I didn't notice it on my car but it makes sense. If the motor is running more efficiently with the added advance it will make a less effective brake. So which should you use? Try both and see which you like best."


basically the only difference is between ported and manifold is the vacuum at idle, they both go away at wot, and are both there at part throttle. i have on all my carb run this way. never a problem, and yes at wot there is no measureable vacuum, put a gauge on once and see. only when the throttle is returned to part or closed will vacuum return

barnett468

.
Both Ford and GM used ported vacuum on millions of cars PRIOR to the emissions laws initiated around 1965. Since there were no restrictions on what they did, and these people are the ones whom designed the engines, it raises questions to the credibility of peoples claims stating that manifold vacuum is better than ported.


sorry but this comment makes no sense to me.


actually, the vacuum advance is also active upon decelleration since this is when the manifold vacuum is the highest . . when properly setup and the vehicle is allowed to coast a little before the brake is applied, this can also increase mileage.


quote from the same article

"Once you have the mechanical advance setup to give you the most power, and no pinging, at WOT then you should setup the vacuum advance."

if you read my post you will see that this is exactly what i am having the op do.


"Most vacuum canisters are adjusted by sticking an allen wrench in the vacuum tube. I had to turn my vacuum advance down until it only pulled in 5°."

I suggested to the op that he use 6 - 8.


Feel free to ask me any other questions you might have regarding vacuum advance and i will try to answer them for you if i have time.
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mdt424

Hi guys!! Well life has its ways of getting in the way of our fun sometimes. Sorry for my delayed response, my dad had to have surgery to remove a tumor from his brain.

Well moving the distributor back a tooth it had a negative result with the car barley running. I put it back and changed the timing three degrees at a time until it started running bad, ended up backing it off about five degrees. The marks on the damper are not even close but she runs well & stays running when shifted into gear! I may still need to change the torque convert but not sure yet as the idle is still about a thousand in neutral. Thank you all for your help! I have another problem now that has me baffled but I will post it in a new thread so this thread will stay focused issue for other users. If you have electrical experience please look for my post. Thank you all again!