Manifold port question

[jscott]

Now that (with the help of a member here) I have Id'd my intake manifold as a   M-code 4V intake. Date code is 1A29, January 1, 1971 so not original to your car.  I have a question on one of the items in the front of the manifold.  I guess this is a vacuum port, which is capped off.  What would it have been used for when the manifold was installed on the engine it was intended for?  It is centered in the picture.

 

[vintageman]

I have the same vacuum port and it is also plugged right now. I saw a video on YouTube today and they said it normally goes to the Temp controlled vacuum port that can be installed in the water pump. Not sure if that is correct though. Watching this thread for further info on this. Thanks for starting this thread.

Tom

 

[Don C]

That was for manifold vacuum to the rear section of a dual diaphragm vacuum advance distributor, either directly or through a ported vacuum switch. You can see the diagrams on pages 10 and 11 in the 1971 vacuum diagrams:

 

[jscott]

With my Mallory dizzy in place I guess I canjustmplug this then, any other suggestions for its use in the vacuum system?

 

[Don C]

No, all other vacuum connections were made on the vacuum tree at the rear of the manifold.

 

[jscott]

Plug it is then, thanks for the info

 

[jscott]

Anyone know the tread pitch/size for this hole?

 

[Don C]

Going on memory here, but I believe it is 3/8" NPT (pipe thread). I know the pipe thread is correct, but the size may be off. If it is 3/8" the outside diameter of the threads should be between 5/8" and 11/16" at the top of the fitting next to the nut.

 

[Stanglover]

If I can stick my nose in here, if the manifold is an M code 4V, what heads are on the engine? Super large ports on the M code 4V will not match up too well with 2V heads if that is what our friend has on the engine. I would suggest that he take off a valve cover and look at the date code(s) That might give an indication as to correctness to the car's build date. Do the heads have a 4 or 4* in the front top corner (left side)? It's unfortunate that Ford decided to cast the head casting numbers and ID on the underside of the intake ports where they can only be seen by removing the manifold, standing on one's head! (or use a mirror). To be honest, I'm not at all familiar with 72/73 heads which are open chamber, but this just got me curious.

As for the port, you don't really need it and it was for the ****** side of a dual diaphragm dist, via the 3 port vacuum temp switch. I have found mine runs best on ported vacuum with the Holley 670 S/A carb I have, so it's plugged off.

 

[goodnigh]

Mine goes to a temp sensor and then to my distributor.

I understand this was used to increase the RPM if the

engine was running hot at idle.  Normal idle would be ~750.

This would increase the idle to 1200 after running the car

then going to rest, stop light.

mike