Valve Cover Oil Fill/Breather Cap

[1969_Mach1 333]

My Scott Drake valve covers have an oil fill tube on one of them.  So I purchased the Scott Drake oil fill/breather cap shown below.  It looks nice, clean, simple.  And it has several 1/4" vent holes around the outside edge of the bottom and a filter inside which is good.  But, it only has two small holes inside the cap at the top to vent into the crank case.  These two holes are smaller than 3/16" diameter.  Does anybody know of another cap that might vent better?  It needs to push onto a 1-3/8" diameter tube.  If not, I'll grease a drill bit and carefully open up the holes in this one.  Apparently caps that push onto a tube are rare these days.

I know my 69 351W is supposed to have a cap with a hose that vents to the air cleaner.  I'd rather use this other type if possible. 

[LoneWolf2U 136]

The cap does not vent to the air cleaner, It is the clean filtered air inlet to the crankcase.

The pvc side is sucking crankcase air out into the intake.

Adding more ore larger holes may help flowing more air, But it should have some filtering on it.

[barnett468 418]

1 hour ago, Mach1Rider said:

The cap does not vent to the air cleaner, It is the clean filtered air inlet to the crankcase.

 

[1969_Mach1 333]

Maybe my question wasn't clear.  Not the first time for that.  I understand how the PCV and crank ventilation system operates, both open and closed systems.  The two vent holes inside the cap seem so small that it will restrict the amount of air flow the PCV is capable of moving.  That's why I was looking for a different cap.

I also have this cap below.  The vent holes inside the top of the cap are much larger on the cap when compared to the other cap.  But, my preference would be to not have to run a hose to the air cleaner like this cap is setup for.  Mostly, because I only know of using 5/8" heater hose to connect it to the air cleaner.  That hose doesn't like to easily conform.  Is there some other hose for this that is more flexible than heater hose?

[gordonr 4]

Since your not keeping the oem set up. I would make the goal of your PCV system in keeping the oil moisture free as possible and the tops of your pistons clean. 

[LoneWolf2U 136]

Then enlarge the inner holes to 1/2 inch and use that cap type.

Test air draw by using a piece of paper with hole that will allow it to slip over the valve cover tube.

Run engine at idle and see if the paper will stick to the breather bottom.

[barnett468 418]

How large is the smallest hole in the pcv?

Some auto parts stores sell chrome caps that may have larger holes.

If I get time today I will see if I have an orig cap and will look at the hole size.

 

[Alan_Mac 48]

18 hours ago, 1969_Mach1 said:

Maybe my question wasn't clear.  Not the first time for that.  I understand how the PCV and crank ventilation system operates, both open and closed systems.  The two vent holes inside the cap seem so small that it will restrict the amount of air flow the PCV is capable of moving.  That's why I was looking for a different cap.

I also have this cap below.  The vent holes inside the top of the cap are much larger on the cap when compared to the other cap.  But, my preference would be to not have to run a hose to the air cleaner like this cap is setup for.  Mostly, because I only know of using 5/8" heater hose to connect it to the air cleaner.  That hose doesn't like to easily conform.  Is there some other hose for this that is more flexible than heater hose?

I have an adjustable PCV installed with this cap.  Finally my crankcase is vented correctly as my cap stays in the fully seated position after WOT blasts.  The air cleaner connection provides a pressure drop to help vent the crankcase.   I recommend not to use a cap w/o the air cleaner connection. 

[1969_Mach1 333]

On the inside of the cap there are only two small holes exposed to the tube the cap fits over.  Using number drills to measure, these two holes are 0.168" diameter.  In my mind I'm thinking the PCV valve can flow more air than can pass through these two holes.  I suspect this cap is a copy of what was used on the 260 and 289 motors of very early Mustangs which is why only two small holes.

Merely going by the orifice in the bottom of the PCV valve:  PCV orifice = 0.3125" dia. and Area = 0.077 sq. inches.  Each of the two breather holes are = 0.168" dia. each and Area = 0.022 sq. inches each.  So the PCV has a much larger flow area than the two holes combined in the breather cap.  I could be wrong.  But this is my logic.  Like I mentioned earlier, the cap made with a hose fitting has a huge open area that is exposed to the tube for air flow. 

[1969_Mach1 333]

22 minutes ago, Alan_Mac said:

I have an adjustable PCV installed with this cap.  Finally my crankcase is vented correctly as my cap stays in the fully seated position after WOT blasts.  The air cleaner connection provides a pressure drop to help vent the crankcase.   I recommend not to use a cap w/o the air cleaner connection. 

I don't have a shaker hood and with a Weiand stealth intake I cannot fit a stock air cleaner under the hood.  I use a Moroso 14" air cleaner to get good hood clearance.  It has a fitting on the bottom for that hose to the breather cap.  But it's not nearly as good of a setup as stock so the hose doesn't fit very well, even hoses with a molded 90 deg. bend at one end.

They reproduce stock 1968 390 air cleaners.  They are expensive, roughly $400 for a base and lid.  I have wondered if being for a 390 it was lower profile than the stock 351W air cleaner?  If so, eventually, I'd like to go that route for a more original look. 

[Alan_Mac 48]

maybe call moroso for a pcv tube recommendation?

 

[1969_Mach1 333]

Moroso only offers the standard fitting that attaches to the bottom of the base.  K&N has some for marine use that go on the outside of the filter assembly.  Kind of just wedges between the air cleaner base and lid.  It's flimsy and usually bends and come off easily when installing or removing the hose.  I've thought about making a stronger version of it. 

 

[gordonr 4]

1 hour ago, 1969_Mach1 said:

I don't have a shaker hood and with a Weiand stealth intake I cannot fit a stock air cleaner under the hood.  I use a Moroso 14" air cleaner to get good hood clearance.  It has a fitting on the bottom for that hose to the breather cap.  But it's not nearly as good of a setup as stock so the hose doesn't fit very well, even hoses with a molded 90 deg. bend at one end.

They reproduce stock 1968 390 air cleaners.  They are expensive, roughly $400 for a base and lid.  I have wondered if being for a 390 it was lower profile than the stock 351W air cleaner?  If so, eventually, I'd like to go that route for a more original look. 

I have the original 390 A/C setup I could measure it later if your interested

[1969_Mach1 333]

1 hour ago, gordonr said:

I have the original 390 A/C setup I could measure it later if your interested

Yeah, when you have some time, a measurement from the flange that sits on the carb to the top of the lid would help.  With that I should be able to figure out if one would fit.  Thanks.

[gordonr 4]

1 hour ago, 1969_Mach1 said:

Yeah, when you have some time, a measurement from the flange that sits on the carb to the top of the lid would help.  With that I should be able to figure out if one would fit.  Thanks.

Came up with 1 11/16". 

[1969_Mach1 333]

43 minutes ago, gordonr said:

Came up with 1 11/16". 

Thanks for the information.  That's shorter than I expected.  Seems like its just tall enough to clear the choke assembly.  I'm guessing they are made to fit over a Holley carb?

[gordonr 4]

1 hour ago, 1969_Mach1 said:

Thanks for the information.  That's shorter than I expected.  Seems like its just tall enough to clear the choke assembly.  I'm guessing they are made to fit over a Holley carb?

Its sitting on an Autolite 4300 but I have a Quick fuel 735 in the box. The A/C actually rubs on  the float adjustment nuts only, the rest is free and clear. A slight modification would work  though.

[1969_Mach1 333]

Until I get an original type air cleaner assembly so I can use the larger cap with a breather hose, I was able to take apart the cap shown below and drill four more 3/16" vent holes on the inside.