Vacuum advace source on a 68 200 with 1 barrell carb

[kevinl1058]

Still trying to figure tis one out. wht would you guys say would be the best source for vacuum advance, fom the carb or manifold. The motor is a 68 200?

 

[Harte3]

It is easy enough to try both ways to see which may work the best.

 

[FalconSedanDelivery]

Try both ( manifold and Ported Vacuum ) if its curved correctly for the application , Ported is 95% of the time a better choice

 

[jamyers]

First, "carb" vacuum could be either manifold (always) or ported (off at idle) vacuum signals, depending on the carb/fitting.

The *only* difference between ported and manifold vacuum is that with ported the vacuum signal is cut off when the throttle is closed (idle).

The only reason the OEM's did that was so that they could have retarded ignition timing at idle, which meant hotter combustion = less emissions.

That being said, I recommend manifold vacuum. But on some engines (carb/tune/ignition), ported "feels" better.

 

[FalconSedanDelivery]

with our beloved Ford 6's ( and most fords pre 57 ) a venturi vacuum was used , why , because there was no mechanical advance in the dist just a breaker plate that moved with the help of a vacuum source that got stronger as the carb was opened , a good ideal , NO but it was cheap and for its time was adequate for everyday STOCK USAGE !! , in 67 ( 57 for most of the v-8s , ford upgraded thier dists with mechanical advance and vacuum became an Econimizer addition in our Falcon 6's just as it had been in most previous combos , including the Big three automakers, However to say that it was only for emmisions is a misinformed statement that I have seen posted here many times, between 1957-and 1966 emission controls ( with a few exceptions wer non existent ) but ported vacuum WAS the Norm , now after Emissions cam into play was Ported vacuum used to help emmissions , yes but only because electronic controls were years off , Curves in Distributers are complex not all encompising as some on this board ( and many other places ) seem to state , I recurve Dist's as a side business , have since 1986 , and previously to that for othe employers ,bending tabs , adding springs of different tension are part of the equation BUT , only part. limiting or adding more initial advance , limiting or adding vacuum applied advance is also included , AND KNOWING WHY , not just how is a years of experence that cant be expressed enough , if you blindly go forward with only the tools and an instruction sheet / advice to go by, you are assuming the knowing WHY parts is not important , and that is a mistake that can be expensive

 

[Harte3]

I ran a Holley 1848-1 4v 465 cfm on my engine for a while (see signature) and it only had one vacuum port on the body of the carb which was timed and I assume a venturi source...ran like crap until I sourced directly to the manifold. My current carb has multiple ports in the base and I use the full vacuum source. It will run fine on the timed port with the throttle plates opened up a bit at idle.

 

[FalconSedanDelivery]

Ok what is the curve in your dist , first the mechanical part what is the initial setting ,what is the total advance and at what rpm does it start and when is itn all in , then your vac adv , when does the advance start when does it finish and how much does it advance , what is your compression ratio, what is your final drive ratio in the vehical , is it a stick or automatic if automatic what is the stall speed on the converter , what are the cam specs , specificaly the duration at 0.50, how is the vehical used and what octane do you run , and last but not least at what altitude do you live those are most of the questions that need answerd to start a recurve , then its the knowledge to apply those facters into modifiying the Dist to get the rsults needed , a mrg 925 and timing light are not all you need