Using Manifold Vac for Vac advance on Duraspark

[salty_monk]

Just bought a "T" piece & some 5/32 Hose to T into the vac supply for the wipers to give this a go.

Any problems where in the run I pull the vac from? It would be neatest to do it right by the firewall but I can go round & do it right in front of the manifold too if necessary.....

Has anyone needed to build an "accumulator" to get this to work? (some kind of larger cylinder in the line to "dampen" the effects a little).

Dan

 

[Asa]

all the advice i've read is to get the vacuum directly from the carb

 

[salty_monk]

I have the wrong carb on there at the moment with no output.

It has a Spark Control Valve for the old "loadamatic" vacuum only distributor instead. That won't work as it will introduce Venturi Vacuum on top of the centrifugal at higher RPM's & throw everything out......

I've read of some having success using manifold vac instead.

What Advance figure should I be aiming at including Vac advance at idle (600rpm). I have a dial back pro series timing light so I can easily measure it once I have the vac connected.

This is a 200ci with DSII ignition & a Holley carb.

Dan

 

[fordconvert]

Mine had the 3/8 steel line that went from the log under the carb over the valve cover and then reduced to a hose that went to the transmission. When I did the duraspark I just put in a T. When I added the power brakes I cut the reduced end of the steel line off and got a T with 3/8 and a 5/16 to still run to the dizzy and transmission. Did not notice any performance change with any of the mods. Brakes work great. Its been that way for almost 2 years.

 

[salty_monk]

Seems it's not important where you add it in the line then.... Tks.

Dan

 

[fordconvert]

I think you could get to a level of performance where it makes a difference but for most of us that are going to drive on the streets and measure performance with a finely calibrated butt dyno I dont think its critical.

 

[JackFish]

Is there not a brass fitting on the manifold below the carb for vacuum?

 

[ludwig]

My spark advance comes off the carb throat and the trans modulator comes off the block below the carb on the log. This block has three other ports that are plugged with blind hoses. I assume at least one is for the power brakes if I had any.

The other would be for my fuel economy gauge for the Mobil Economy Run.

 

[JackFish]

Heheh, here's a vacuum fitting for ya!
'76-'79 250 Granada, Monarch et al...

 

[HARVEY LIGHT]

so - what is the part number and where did you get it?

 

[JackFish]

so - what is the part number and where did you get it?

D67DX-9A474-3

Got it on ebay.

They are hard to find in good, or new condition.
All the others I have collected are pretty ugly.

OT: I wish I could find some original water pump fittings.

 

[salty_monk]

Anyone know what advance at idle (600RPM) incl vac advance should be? I have a dial back light so I should be able to measure it when I connect it up.....

 

[fordconvert]

There are 23 distributors with varying specs listed in the 66 shop manual. Some are obviously for the V8's but they all show 14-16* for the mechanical and 6-14* for the vacuum. The load o's look like they were 12-14* range.

Those numbers should give you a range to try and stick with. There is no perfect number to set them to because there are too many variables especially at this age. If you take the 16(mech)+14(vac)+12(base). That gives you 42 which seems like too much to me. If I read closer I would guess that the totals with the various combos is going to be more like 35. Check the range in the vacuum, most of the time if there is too much its going to be there. It must be due to crappy tolerances and a one size fits all mentality with the aftermarket people. At idle you should just have your base and the vacuum which I would expect to be around 20 if you are running manifold vac. It helps to think of the vacuum as a retard instead of an advance. Acceleration is mostly in the mechanical because the vacuum drops under load and acceleration. Cruise is where the vacuum comes in. Just to make it more fun fuel and timing interact so you can cover one problem with the other. Thats one thing I love about EFI, you can try something new just by hitting a few keys. If it does not work you just hit a few more keys and put it back the way it was. Beats the heck out of tearing apart the carb to change jets and the dizzy to grind things and swap springs. Either way remember to take notes and base line readings so you can go back to what worked if you have to.

 

[66 Fastback]

At idle on a Manifold Vac source, you would probably see in the range of 25 deg crankshaft advance. That would be the combination of static initial timing +/- 10 deg and vac advance +/- 15 deg.

If you take the 16(mech)+14(vac)+12(base). That gives you 42 which seems like too much to me.

As far as the total of all of the advance 42 degrees is not that odd for a car under light throttle at highway speed. Some of the leaner carbureted engines of the emission era have total timing advance into the 50 deg range under those conditions.
Doug

 

[MustangSix]

If you use manifold vac, you have to set initial timing with the vacuum disconnected. If you don't what happens is the vacuum advance will pull full open, and you set the initial timing to, say, 12 degrees. As soon as you hit the gas, vacuum drops to nothing and ALL your initial timing goes away and possibly then some. The result is a big bog, a backfire, or just generally poor running and economy.

Once you have the initial set and the vac hooked up to the manifold, the reading may be in the 26-28 degree range at idle, but that's ok. It will drop under load, the centrifugal will pickup over speed, and the vac advance returns as load decreases. 42 degrees would only occur at a relatively high speed with your foot off the gas.

This technique DOES NOT work with the Loadomatic. Vacuum advance alone is not sufficient and it will make enough advance under load without the venturi vacuum in a matching Loadomatic carb.

 

[salty_monk]

Thanks guys, that's what I wanted to know

I have 10 degrees initial right now & no vac connected, it's running pretty good. I just got the bits to connect up the Vac so will do so soon & leave the base at 10 for now, see how she runs

Sounds like I "may" get away with a couple more degrees of initial but I'm not running premium gas

 

[salty_monk]

Well the Vac advance on my Dizzy seems to give 15-16 degrees of advance measured with my light.

Vacuum line T'd into wipers at the firewall. Idle is now much smooother, had to wind the stop in about half a turn or so.

Going great now! All I need to do is get my disk brakes delivered & on there so I can stop!!

Thanks for the help