Close



Results 1 to 11 of 11
  1. #1

    Default Opinions on PCV Valve

    So I have been playing around with different PCV valves on my carbed engine. I had a mystery valve that I thought was from my old 302 but it seems to flow way too much air at idle. This is quite noticeable on both the wideband (lean) and if you put your hand over the other grommet on the valve cover it will pull a pretty good vacuum on your palm after a second etc...so it is doing its job vacuuming the crankcase I get it, but seems excessive to me. I realize that vacuum is maximum at idle and cruise but shouldn't the PCV valve should limit this flow accordingly ?

    So thinking I had a much bigger than normal PCV valve or something I ordered a replacement for a 79 mustang 302 but same thing it seems to move too much air !!

    The other issue is that this seems to suck a bunch of oil into my carb spacer where I have a port for PCV etc. I tried putting an oil mist eliminator in the line and it will build up some oil (probably a tablespoon or so) after only a short 50K trip and that seems way to much.

    Never really noticed these kind of things before I got playing with the wideband. I suppose before the oil mist carryover was just burned off but at that rate if normal it wouldn't take long to be down a quart in my opinion. Not to mention its probably not greatest to burn the oil if it can be helped.

    So I'm curious what's normal and/or what others have experienced or done etc ?

    Thanks in advance.

  2. #2
    FEP Power Member Ethyl Cat's Avatar
    Join Date
    Oct 2010
    Location
    Lebanon, IL
    Posts
    1,240

    Default

    I would adjust pcv valve flow as a way to get the primary throttle blades into the proper position in relation to the transfer slot not for AFR adjustment. Kind of a away to not drill holes in the blades to get bypass air.

    You have idle mixture screws for afr adjustment.

    Is your engine stock or built?

    Another option if you want to play with pcv valves are the fixed oriface LS style pcv valves.
    BBD PERFORMANCE
    HIGH PERFORMANCE PARTS
    CUSTOM ENGINE BUILDS
    CUSTOM CAM DESIGNS
    1983 CRIMSON CAT OWNER

  3. #3

    Default

    Ok yeah makes sense if I can get the right flow for the idle screw setting. I suppose if it’s consistent it can be adjusted. It’s a bit of a built up 302. Nothing real crazy, aluminum heads, edelbrock rpm manifold, 600 cfm carb etc, but I retained a stock 95 roller cam so still have 17 or 18 “hg vacuum at idle etc.

    I see they make adjustable pcv valves but pricey. I was thinking of restricting the line with an orifice of some sort as I think it’s a bit too much. That may help the oil situation as well. Still experimenting.

  4. #4
    FEP Power Member Ethyl Cat's Avatar
    Join Date
    Oct 2010
    Location
    Lebanon, IL
    Posts
    1,240

    Default

    Make sure your valve cover the pcv valve is in has a baffle in it below the valve. That could cause the issue you are having.
    BBD PERFORMANCE
    HIGH PERFORMANCE PARTS
    CUSTOM ENGINE BUILDS
    CUSTOM CAM DESIGNS
    1983 CRIMSON CAT OWNER

  5. #5
    FEP Super Member cb84capri's Avatar
    Join Date
    Jan 2003
    Location
    lansing, mi
    Posts
    4,667

    Default

    The pcv valve on my Capri is a Motorcraft EV-140, because anything that is model specific for my car has the ugly outlet "antler" on top of it. Application is 1987-1996 5.0 F150. Baffled valve covers are a must, I modified the ones in my aftermarket valve covers so they have smaller openings. Also I have a cheap filter / water separator used for compressed air with a screw off bowl inline of my pcv to help separate the oil out of the vapors. I have the filter removed from it, and it It seems to do a nice job of keeping deposits off of my intake valves but my car only ever sees top tier gasoline. My old 302 had a high volume oil pump in it, and I used to empty it frequently. The 347 in it now has a standard volume, and I seldom ever have to empty it.

    Do you recall what intake manifold gaskets you have in it? The majority of what is available for these engines don't hold up well. My old 302 was drinking a lot of oil through a failing set of standard Fel-pro 1250 gaskets. I now use Fel-pro 1262s3 with the steel core.

    Cale

  6. #6

    Default

    Thanks for the tip on the valve I don’t believe these were all created equal and who knows with the aftermarket etc.

    I have aftermarket tall valve covers with roller rockers with baffling. I rigged up a piece of hose with a screen and breather material under the pcv to try and coalesce the oil must a bit. It doesn’t restrict the flow much but was hoping it would drop some of the oil. I have the 1250s3 for that exact reason I didn’t like the plain 1250s. I am running a hi volume pump though.

    I tried cutting an end off an old pushrod and putting it after my pcv valve as a restriction. I figure it acts as about a .090 orifice. Much less air moving now and I adjusted idle etc accordingly. Will see what that does.

  7. #7

    Default

    Ok I got things setup decent I think. The restriction definitely changes things as far as bypass air and idle settings etc but it has helped the oil carryover quite a bit. I am pretty sure my intake gaskets are good as I get no vacuum at all at the breather with the pcv valve disconnected. It actually gives a bit of a puff if you rev it up so thinking that is normal. With the pcv and restrictor I get a very slight vacuum on the crankcase at idle and if I rev it a bit etc.

    I suppose the drawback to the restrictor is you limit flow at part throttle to wot but if I understand it correctly it should still vent positive crankcase pressure to the breather if it needs and get sucked in at the air cleaner. No evidence of any oily film there yet.

  8. #8

    Default

    Decided I could go a little bigger on the flow so I rigged up a 0.130 restrictor orifice and adjusted mixtures. Seems OK I got a little more vacuum on the crankcase now.

    I would have never thought the PCV valve and flow would make as large a difference as it does. Goes to show using any old PCV valve may drastically affect your engine.

  9. #9

    Default

    From Chilton's General Manual 1970.

    Fixed orifice sizes to substitute for PCV Valve Testing at idle:

    Engine (cid).......Hole dia. (in).......Fractional drill
    90 to 140 ......... 0.056 - 0.075 .... 1/16
    141 to 200 ....... 0.074 - 0.088 ..... 5/64
    201 to 275 ....... 0.087 - 0.099 ..... 3/32
    276 to 350 ....... 0.098 - 0.112 ..... 7/64
    351 and up ....... 0.111 - 0.125 ..... 1/8

    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  10. #10

    Default

    Good information thanks !!

    Looks like I was in the ballpark with my fixed orifice sizes at least then.

    However, this kind of proves the PCV valve (or at least mine) really isn't regulating the flows very good on its own. Makes you wonder how often this small item is overlooked or taken for granted.

  11. #11

    Default

    Further to this topic I just realized that it makes quite a difference on which vacuum port you connect the PCV valve.

    I was using the vacuum connection on my carb spacer(which is basically a full size hole) and had way more flow through the PCV than when changing to the carb port which must have more of a restriction etc. This explains why the differences in flow that I never really noticed before I added the adapter plate and plumbed the PCV there instead etc.

    My assumption was that the PCV valve would regulate the flow regardless of the port size, but it is night and day difference switching the hose between the carb vs spacer ports.

    Using the carb port I get a more proper flow/crankcase vacuum without need for the restrictor...so something to keep in mind when using spacers or different carbs I suppose.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •