1974 Ford F100 with a 390 engine

I’ve read up on the PCV system on these engines in the forum. My current set up is the vent on the driver’s side and the cap on the passenger side. From what I’ve read, I can add a PCV valve to the passenger’s side and run a vacuum hose to either the carburetor or intake manifold.

The transmission modulator is connected to the intake and the brake booster to the carburetor. I don’t see any other places to connect it on either of these. If I’m missing something, can someone point that out to me?

My thought was to use the underside of the air filter housing. Can I purchase this barb and connect the PCV to it? If I can, are there disadvantages to doing so?

https://www.summitracing.com/parts/s...RoCOwYQAvD_BwE

 

Looks like you have 2 LH valve covers. FE covers are cheap just get a RH one and hook it to the grommet as it should be.

The breather on the LH side should be hooked to the air cleaner housing. but it doesn't have to be.

 

The breather that connects to an air cleaner does so to filter air before it enters the breather / engine on one bank. There are breathers available that include a filter and need no connection to the carburetor air cleaner. The PCV should be on the other bank so that between the two, the fresh air from the one is pulled through the crankcase to exit with any crankcase vapors. There is notr enough vacuum in an air filter to adequately pull vacuum on a PCV, it needs intake manifold vacuum. Do not tee it off a power brake booster vacuum feed, Look or feel around at the base of the carburetor in back, feeling for a 3/8" hose bib with a rubber cap maybe, so Holleys had them. I used to pull my PCV vacuum off the #5 intake runner, but I finally plugged that fitting and installed one into a carburetor spacer in the back just to pull the PCV.

A PCV has a lightly spring loaded valve, it only opens under higher vacuum like coast or light cruise, at heavier throttle the manifold vacuum drops and the PCV shuts.

 

These are stock pictures of holley 750. The rear seems to have just the one port that I'm using for the brake booster. The front appears to have two with rubber caps. If they are actually on mine and the larger one is 3/8", does that work?
So leave the cap on the driver's side (it has a filter) and run the PCV from the passenger side to a port on the carburetor if I can find a place for it?


If there isn't another port I can use on the carburetor, you added a spacer to provide one?

 

The larger port on the front is meant for the PCV

 

If it turns out that your carburetor only has the one 3/8 inch port, utilize that for the PCV valve and create another location for your brake booster.
The single port in the intake manifold that you have your transmission modulator connected to, should have a vacuum manifold, or “vacuum tree“ screwed into it instead of a single fitting. The “tree“ will have multiple vacuum ports.
You should be able to find several different designs in a junkyard, or maybe they sell them new online nowadays. I haven’t had to look for one, but I assume they can be found without a separate trip to the junkyard.

 

Is that a hole in the center of the cap on the driver side valve cover? If so, that was probably originally intended for the PCV valve.
Probably the right size hole for a rubber grommet to hold the valve.
The “filter“ media in that may not be for clean intake air, but may be for capturing/condensing extra oil vapors that get past any baffles in the valve cover.
Is it just a coarse bundle of metal strips inside?

 

Manifold vacuum is the same from either of those large ports. My statement about the brake booster vacuum being alone on it's fitting is I don't want a fluttering PCV on the same feed, even though "manifold vacuum is manifold vacuum". I'd maybe run my brake booster off the rear large port if using that carburetor, and my PCV off of the angled front large port. The smaller angled port would work well for a transmission modulator valve too. Distributor off the higher up ported tube on the metering block. If you still need a place for heat/ac control vacuum, it could be teed off the PCV or modulator lines. Any fumes pulled in from the PCV line are going to go down into the intake plenum under the carburetor either way as both of those large fittings will have the same vacuum strength.

I favor the rear, less restricted port on the carb base pictured only because it puts the brake booster hose out of the way and with larger passages, can get the large booster evacuated of air quicker after / during use. The angled large port is pointing to the passenger side where my PCV is anyway. My old Holley carburetor did not have large ports, so I got a spacer and added one. My brake booster vacuum comes off a tree on my intake in back below the carburetor mount surface. I only needed a large 3/8 port for my PCV. I used to run it off the intake manifold on a fitting that was to cyl #5 but I decided to plumb it more central so all 8 cylinders could share. My Edelbrock carburetor does have provisions for both PCV and PB Booster, but I block them.



Disregard the red and yellow. Just something I added.

 

Your booster and modulator line need to go together on manifold. PCV goes where your booster is now. Driver side breather can vent into air cleaner if you have a blow by problem. Factory Ford intakes are cool in that they drill into both planes of the intake under the tree ports. Aftermarket you have to adapt. Spacer or your present carb can do the same. JMO

 

You can put them wherever you want but Holley literally labels that rear port as being meant for the brake booster, better than pulling off of a single intake runner. And it just so happens that the front 3/8" full manifold port is angled so that the PCV hooks up to it nicely.

 

Yes that cap on the driver's side has a hole in it with a course woven metal material inside. I agree on it capturing vapors as I can see vapors escaping when the motor is running.

 

So I have a larger plugged port on the front of the carburetor. Would this be the setup I should use? Breather cap on the driver's side, pcv valve on the passenger side (where the yellow arrow is pointing) with the vacuum hose connected to the front port on the carburetor? Also, should I leave the breather cap (or something similar) or install an elbow and run a vacuum hose from it to the air cleaner?

 

You can run hoses to an air cleaner, but they will not provide vacuum.

How I have mine and why. Just a yellow circle push in PCV on the passenger side, 3/8 hose to carb fitting, and my driver side has a push in filtered breather cap. I do not have a red hose to the air cleaner, as my cap has it's own filter, that I clean occasionally. Green air being pulled through the engine gathering particles of crank case by products to be sucked out through the yellow PCV and into the carburetor / intake during high vacuum, low throttle operations like coast or idle ... to be burned. It is why too that you replace a filthy PCV occasionally, or at least clean it ... it is a calibrated vacuum leak.

 

tbear has the correct answers. Your current breather cap probably had a fitting on it as shown below that had a small hose connected between the cap and air cleaner. That's the rest of a fully closed system you don't have. It's not necessary unless you're in an area that does a visual check for emissions equipment or you're concerned about a slight atmospheric vapor leak. A breather cap that allows clean air to enter the engine is all that's necessary.

 

Thanks for all of the information. I'm going to find all the parts I need and get it put together. I'll post some pics when it's all done. My only concern is making sure I find the correct PCV valve as I have read stories about those who bought the "correct" one and found out after running the engine that it wasn't when leaks started to appear.