Duraspark distributer vacuum line

[Jutter]

I am doing a duraspark conversion to my '84 bronco II. I have collected all of the parts and read the articles on how to do this conversion but it is unclear to me where to hook up the vacuum advance for the distributer. One article says to hook it up "above the carb plates" and Another tells me not to hook it up at all. Is there anyone who can shed some light on this subject?

 

[dangerranger83]

Hook it to manifold vacuum.

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[cammeddrz]

I say, leave it un-hooked, the vacuum advance is for fuel economy

 

[kimcrwbr1]

The vacuum advance is for performance not economy. You can hook it to either the vacuum tree (manifold vacuum) or ported off the carb normally the port out the choke side on the base of the carb. At around 700 rpms and the vacuum hose disconnected and plugged from the distributor time the engine at 10 degrees. Then adjust the idle air needles on the carb for the highest possible vacuum or rpms. Allways adjust the idle air needles after you change the timing.

 

[martin]

The vacuum advance is there to retard the timing under low rpm, high load conditions. Under light load conditions above around 1500 rpm, the motor likes around 38 degrees of advance. If you floor the pedal and you still have 38 degrees of timing you will get spark knock or detonation, the vacuum will prevent this by retarding the timing by anything up to 12 degrees.
Whether you connect the vacuum to ported or manifold makes little difference under normal running conditions. Where it does make a difference as at and just above idle.

 

[cammeddrz]

The vacuum advance is for performance not economy.

^^wrong, you are so wrong that the opposite is literally true

seen many places such as here: http://en.wikipedia.org/wiki/Ignition_timing

Vacuum timing advance

The second method used to advance (or retard) the ignition timing is called vacuum timing advance. This method is almost always used in addition to mechanical timing advance. It generally increases fuel economy and driveability, particularly at lean mixtures.

just because performance can be increased by increasing overall advance, doesn't mean that something with "advance" in the title automatically increases performance.

and yes, the mechanical advance is directly tied to performance

but vacuum advance literally doesn't even work under throttle. even if it was attached to manifold, or ported vacuum there is literally zero vacuum at wide open throttle, and barely any even at 1/2 throttle. so are you talking about it helping your "performance" at idle/less than 1/2 throttle? I can't help but think that "performance at idle" is a contradiction in terms.

 

[Jutter]

Thanks for all the info, I will explore these options and see what works best.

 

[kimcrwbr1]

I just go by personal experience with the 2.8 and my truck runs best at 10DBTDC base timing with the vacuum advance connected to ported vacuum on a nonfeedback carb. The best gain in performance was putting in the #42 high speed jets and adjust the idle air needles for the highest rpm possible then set the idle stop for 700 rpms and adjust the needles again. turn out and then in until the rpm just begins to drop. If you can get 18hg in vacuum at an idle you should be set.

 

[martin]

I guess I'm the only one that's ever run with a vacuum gauge on the dash..

 

[dangerranger83]

Hook it up and be done.

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[Daniel84RangerXLT2.8l]

I can speak from experience only, Jutter: Having the vacuum attached makes starting a whole lot easier, especially on cold mornings.