vacuum

[doobspanel]

hi i'am working on a 1951 panel with a 235 from a 1957 car. sm 420 trans.

the motor has been rebuilt using a mild comp cams, dual zenith 28s with a edlebrock intake, and fenton duals.
i want to install the PCV system described in this forum and i have a couple questions regarding vacuum. first, i need to connect the distrubutor to a vacuum sorce. i have read various opinions on where this can/should be done. the problem i'm having is the zeniths don't have a vacuum port. so can i pull vacuum off the manifold for the advance? also, can i split that same vacuum for the new PCV or should i stick with the old style crank tube?

please be advised, this is new territory for me and thanks to forums like this, i'm finding my way but, if i've described something that sounds like i don't know what i'm doing well, i don't!

[Deve]

Doob... the cool thing about this hobby is the different configurations that are possible. I had no idea the Zenith Carbs have no vacuum port. I didnt know ANY carb of this vintage was without a vac port. That being said, Air goes in the throat of the carb, due to the Venturi effect, suction happens and off you go. I do not THINK (someone please correct me if I am wrong) it makes any difference if it comes from the upper intake(Carb) or the lower intake (Vac NPT port on the intake manifold). So, I would run the Distributors Vac Advance AND the PCV from the intake manifolds port. FYI, out of the STOCK 20 inches of mercury available in vacuum, the PCV takes only 2 using the V-237. That is really an insignificant number and should be no problem.

All that being said, I am not a fan of dual carbs and dual exhaust because it has been proven over and over that they do not give you even ONE horsepower more performance due to the way the stock 235/261 Heads are designed. Until someone makes a performance Head, its all show and ZERO go. Just being honest. I dislike them from the perspective that they cause you to have to change the way your shifter works, the way you add oil filter kits, and the way you deal with trailer hitches and other under the vehicle items. BUT, we deal with it because people LIKE them. I did not want to be the first person to respond, was hoping a real expert would chime in first, but wait a few days and hopefully someone like Dave will respond. Hope this helps, but wait for someone who really knows!

[Pre68Dave]

Are you sure your carbs don't have a vacuum port?
On the Stovebolt forum Showkey shows where a 28 port is.
I do not think you will find any problem picking up vacuum for the vacuum advance off the manifold.
In this pic I made a special fitting for a PCV and wipers, but doing something similar for the vacuum advance would work.

Originally most of these engines got vacuum from above the throttle butterfly.
That meant that the vacuum advance only got vacuum once the throttle/butterfly was opened.
By tapping directly into the manifold for vacuum means that the vacuum advance will get vacuum even at an idle.
Since you are over carburating your engine with two carbs, you may find it runs better with the timing advanced at idle, it may give a more complete burn.

[Deve]

Thereyago Doob! As you can now see, I do not know it all. I have never seen a carb without a vac port. I would ask for my money back if I ever found one. So in my haste to make orange juice out of oranges, turns out there IS a good reason to get the vac at the carb as opposed to the intake. I hope panic at Stovebolt helped you with that, and as usual, Dave's testimony is always so spot on and very much appreciated!