Hi, I'm new here but I've been lurking a while. I have a 75 F250 with a 360 and I'm struggling to find information on an aftermarket air cleaner. The carb is a Motorcraft 2100-D and the current air cleaner is an old aftermarket one. I have two questions:

1. Will any air cleaner fit? Some list different diameters (is mine a 5-1/8?) but on my current setup the bottom piece of the air cleaner is indented in order to fit the carb. Is this only a Ford thing or will any air cleaner include these indents? I read somewhere that the carb is odd and has something on the sides, which is apparently uncommon but I'm not really sure about anything.

2. I've noticed a lot of people talk about PCV hoses and such that get fed into the the intake. I don't have a hose, just a chrome cap on the valve cover. Is it necessary to vent that back into the intake?

Sorry if the first question isn't clear, I can provide pics tomorrow if it helps. Thanks in advance.

 

Typical 2V and 4V carbs both have 5.125-inch bases. Most any aftermarket, open-element air cleaner will work and will usually spec' the neck size.


Be advised the bases of some air cleaners are 'dropped', raised, or flat. Take a look at the housing you have an determine which style it is. It is likely flat.


For size, I suggest a 14x3 filter and housing.


The PCV system can source air (intake) with an "open" system as in an open breather or a closed system with a hose leading to the clean/filtered air side of the air cleaner housing. Some air cleaners will include a fitting for a closed system.


The PCV is a check-valve. It's hose is connected to a vacuum source to evacuate crankcase vapors and introduce that vapor into the combustion cycle to be burned. It is important for a street engine that you have a functioning system.


I suggest Googling to get an understanding how it works in more detail than what I posted. The above however are the basics.

 

You want the tallest filter that will fit dont go with those skinny or small VW looking filters. Other that that as long as it fits your good.

For PCV venting it is a must!!!

 

What HIO says is spot on.

A couple more details on the PCV system:


You should have a breather (whether it's a cap with a built-in filter like you've got, or a cap with a hose running to the air cleaner) on one valve cover (typically the one with the cap towards the firewall). The other cover should have a PCV valve in its oil cap - the hose from that valve should run to manifold vacuum at the base of the carburetor.


The system is intended to evacuate the positive crankcase pressure that builds up due to blowby, and redirect it to the intake rather than venting it to the atmosphere - it was the first automotive emissions system mandated in the US, as most of the hydrocarbon emissions before that were due to oil mist from crankcase draft tube vents. They valve is actually a double-acting check valve: it doesn't allow any flow from the intake to the crankcase ever, and will close against pressure in that direction. It also closes in the other direction at very high vacuum (idle) to avoid an excessive vacuum leak. It's basically open during mid-high load operation, so that blowby gases can be reingested.

 

Thanks guys, that was a pretty quick response. I just went out and checked out the setup. I'm pretty sure that the bottom is a "drop base", but it has an indent so to say. The best example I found was this air cleaner, and they call it a "3/8 deeper flange".

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In response to bkaul, there is a hose from the passenger side valve cover (closer to firewall) leading into the carb, and the driver side valve cover has a little filter. I'm sure it's fine that they're switched compared to what you said, right?

Also, I measured the base of the carb and I'm almost certain that its just below 6", maybe 5-3/4.

Thanks again guys.

EDIT: Alright being the genius that I am (sarcasm) I just realized that I can run a flat bottom air cleaner without issue, it's only a drop base one that would require that indent.

 

Ok so I guess I'm bad at measuring because everywhere I've looked says its a 5-1/8" (my apologies HIO Silver). The biggest concern I've seen is that the brake booster is close to hitting, but I think it will be fine. Thanks again everyone.

 

Yeah, makes no difference functionally which valve cover they're on - what I listed is just typical for the factory setup.

 

There is no filter of any kind.

There are two possible PCV routings for 1973/76 F100/350 360/390's. One is the same as 1968/72 F100/350 360/390's

1968/76: Right valve cover has a rubber grommet, smog valve fits into grommet, smog hose routes from valve to elbow on air cleaner.

Oil cap fits into left valve cover, rubber grommet fits into its center hole, plastic elbow fits into grommet, smog hose routes from elbow to nipple on carb.

1973/76: Right valve cover has a rubber grommet, plastic elbow fits into grommet, smog hose routes from elbow to nipple on air cleaner.

Oil cap on left valve cover has a rubber grommet, smog valve fits into grommet, smog hose routes from valve to nipple on carb.