can you school me about vacuum dist advance ?

[Musicman]

The vacuum advance adds more timing to the engine under light and/or no load (Lean Burn Conditions) to increase the efficiency of burn, thereby increasing performance, gas mileage, and lowering engine temperatures. It is a load dependant device, and that's all there is to it... If your engine is idling on ported vac, it is in a Lean Burn condition, generating excess heat... Chrysler was obviously aware of this, which is why they added the vacuum switch to many of their later vehicles. Which makes you wonder...

[Nacho-RT74]

ok, my cam is the Crower 282HDP, iddles nice but with a nice small jumpy shake, hard to notice if you don't open the hood. I guess must be above the 15Hg range you stated.

Sooo... timing my dist/engine, Should I try to find HOW MUCH the vacuum advances before set the weights into my dist, right ?

I thought as mentioned somewhere in some other thread, the vacuum pot on stock Mopar location worked just on the initial throttle open process and then getting thottle steady no matter the RPMs or speed, gets back to rest position.

[bakerhillpins]

I have a 70 block in my 69 that I believe has been modified. I don't know what is in it. I suppose that's the problem. Pulls maybe 11" at idle and has Vacuum advance. Sounds like I need a mechanical advance. 

   Ugh the more I read about this the more I realize I don't have enough "free" time to wrap my head around all this. I am sure it is not that difficult, it rarely is. I just don't seem to have the time to fiddle with things and progress through the learning curve.

[Paul G]

So something concerns me. As my engine is set up right now,

The base timing is 15°,
The total timing is, base timing of 15° + 21° additional mechanical advance, for a total of 36°, all in by 2000 rpm.

If I hook up the vacuum advance to the manifold vacuum port, base timing is going to go up by what ever amount the vacuum can on the dizzy is set up for. In my case it's 10°. It would then idle at 25°. Total timing would be 46° when the engine is above 2000 rpm and when just cruising at part throttle.

Doing that in the past has just landed me right in the heart of downtown "ping city". What am I doing wrong?

[Musicman]

Ported and Manifold vacuum are the same at cruising speed... unless you can cruise at speed with your foot off the gas.

[Chryco Psycho]

not true IMO , cruising you have low air flow / slow air speed  though the venturi as the throttle is mostly closed usually around 20% so the manifold vacuum should be significantly higher

[Paul G]

I did some experimenting today. Went and got some vacuum line, hooked up the distributor vacuum advance to manifold vacuum. Used the port on the front of the carb base plate. Holley carb.

Backed out the screw inside the distributor vacuum advance diaphragm, used a 3/32 allen wrench, till it would only pull about 10° more timing at idle when the vacuum line is connected. Total timing when revving to 3000RPM is off the scale now. Some time ago I scribed a line 2 1/4" from the factory timing mark on the damper. Did this to check total timing since I don't have a degreed damper. The scribed line is almost off the scale. It's normally at the "zero" on the scale without any vacuum advance.

With vacuum hooked up, readjusted curb idle to 750, readjusted idle air mix to highest lean idle. Had to back off the idle adjust screw to compensate for the advanced timing at idle.

Went for a drive. The engine seems to really like being further advanced at idle. Idles smoother, throttle response seems about the same. Got no "pinging" or "detonation" at cruise speeds either this time. So far so good. We will see if MPG comes up, or not?

Last time I tried to use vacuum advance I had other issues with the distributor. Mechanical advance was coming in way to soon. That issue is resolved.

I mainly did this experiment to see if the engine will run any cooler around town. I hope it does, needs all the help it can get, 105° out today and only getting "HOTTER". I did not really drive far enough this morning to get a good heat soak. Last night we went to cruise night, 15 miles from home, all surface streets. I was running at 220° by the time we got there, A/C on. 

Thanks Natcho for starting this thread. I learned a lot! (always learn a lot on this forum)

BTW, found this piece about Mopar timing set up. Long read but informative for the novice.

  http://tvmoparclub.com/files/tech/Mopar%20Timing.pdf

[AKcharger]

Mine is disconnected, seems to run OK 

[AirborneSilva]

I connected mine from ported to manifold the same way Paul G did, I didn't play with my distributor though.  It seems to have smoothed out the idle a bit, not sure if it really went up in RPM's, wish I had a tach! 

[Nacho-RT74]

I was amazed how much a stock vacuum pot advances the timming. I have got around 3 full turns to my vacuum screw ( have read every turn cuts down the timming around 2 or 3 degrees ) and still some SMALL pinging on hard acceleration with load and lower high ( more athmospheric pressure ). HOWEVER CHANGES HAS BEEN NOTICEABLE TO BETTER.

[mauve66]

my mopar perf dist always worked fine with the sixpak setup and the vacuum connected, never new the diff between ported and manifold so i don't know what it was connected too but probably stock, everyone told me to disconnect it for more performance and leave it connected for economy, at 10-12 MPG i needed all the economy i could get

[resq302]

I disconnected mine and plugged the hose.  I didn't buy my charger for economy!     Although I could probably get more MPG's if I lay off the 4 bbl more and just use the front 2 most of the time.     But then again, where is the fun in that!

[Chryco Psycho]

that is what I adjusted on you dads chall too , dialed the vacuum advance way back so it could not advance as much then advanced the timing at idle . What was that 3 years ago now ?

[resq302]

yup.  2009 when my charger was in the dealership display.  my how the time flies!

[Nacho-RT74]

just to be sure... to shorten the vacuum timming, the link Paul provided says turn to right ( in )... that means CLOCKWISE, right ?

I'm having still pinging, under load, at diff RPMs rate, at maybe 600-700 meters height. Weird is that I have got pinging going down the hill with small load ( going maybe 60-70 MPH ), not just going up, where more load is achieved.

ON Caracas height ( 900 to 1K meters ) so far so good I haven't found pinging no matter load or speed, so that's "fixed"

My actual springs set up is orange and purple springs, and 20º key on mechanical as far I remember ( 12º initial )

http://static.summitracing.com/global/images/instructions/maa-29014%282%291.pdf

[Chryco Psycho]

CCW reduces vacuum advance , you have approx 14 turns available each is approx 1 degree , each turn out limits the amount the diaphragm can be pulled by vacuum .

[Nacho-RT74]

so its counterclock!!!!! I was doing it backwards!!! clockwise!!!!

Now I understand why I'm still getting pinging!!!!!!!

really ? I was read one full turn maybe 2 degrees!!!!


Chryco... Dunno if you know or remember my engine setup. But what do you think about my dist springs selection ( remember is street driven and just some WOT for fun )

I don't have at this moment at least, vacuum gauge or pump! but would wish a NICE initial set up to go better on each try. Untill get the vacuum tools

[Chryco Psycho]

not sure on the springs , are you using an MSD dist ?

[Nacho-RT74]

MP... the link I posted above is from Mallory who suposelly is the MP dist manufacturer...

HOWEVER TODAY grabbing on the dist recurve kit, found I have more springs there than the Mallory instruction sheet states. the ones extras are: two light blue ( maybe gray ? ) two silver ( or maybe these are the gray ? ) two more what DUNNO IF are brown or red, but I know I have the browns around, plus one thick spring silver and one green... and couple more light springs without color.

Plus the purple and brown it came out from the MP dist originally

I CAN'T FIND MY ORIGINAL MP DIST RECURVE KIT INSTRUCTION SHEET!!!!!

[mauve66]

are you talking about this sheet with the degree markings for the springs attachments??

http://www.mrgasket.com/Portals/0/downloads/accel/pdf/ACCEL_Instructions_mopar_distributors.pdf

i know this is from mr gasket but talks about mopar dist and i don't know that they make them, hope its some help

[Nacho-RT74]

No, thats diff... never have seen that before.

getting back top original topic I found this

http://www.gofastforless.com/ignition/advance.htm

and here what he shows about the ported and manifold vacuums

http://www.gofastforless.com/ignition/vacuum_chart.jpg

[elacruze]

From my experience ; trying to tune vacuum advance with anything but a stock engine is useless. The vac advance cannisters are designed for engines that make 15hg (or more) of vacuum at idle. 

Once you install a bigger cam the idle vacuum is reduced and all the associated tuning issues rear their ugly head.   


Ron

Having my VA connected to manifold was the ONLY way I could get the timing where I needed it. Without the VA I'd have high idle coolant temps and very rich cruising mixture (read poor-er mileage)

[Paul G]

http://www.gofastforless.com/ignition/advance.htm

Acording to this article, to find the correct total timing you can use your MPH at the end of the quarter mile. He says to increase your timing until your trap speed drops off. Then go back to the point you achieved your highest MPH. That is good information.

[elacruze]

http://www.gofastforless.com/ignition/advance.htm

Acording to this article, to find the correct total timing you can use your MPH at the end of the quarter mile. He says to increase your timing until your trap speed drops off. Then go back to the point you achieved your highest MPH. That is good information.

But that's only WOT timing, which has little to do with daily street driving. (not saying it isn't good info)

[charger Downunder]

CCW reduces vacuum advance , you have approx 14 turns available each is approx 1 degree , each turn out limits the amount the diaphragm can be pulled by vacuum .

I found this to be true regardless of the books you read they have it around the wrong way.