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Author
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Topic: PCV system
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craigber
Journeyman Posts: 78
From: Vancouver, Canada
Registered: Sep 2000
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posted 11-02-2000 12:23 PM
   
hi guys,have a vague understanding of the PCV system on my 351C but would like to actually understand more about the theory and how it affects power, gas economy, emmissions, etc. have recently disconnected the hose from passenger side rocker cover (used to go to old air cleaner) and added a K&N breather...would like to know if this is best setup or not...what is the optimal setup?? like factory or did they dumb it down for various reasons like emmissions, etc.
thanks
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Craigber
71 Red Rag
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Moneymaker
Administrator Posts: 19751
From: Lyons, IL, USA
Registered: May 99
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posted 11-02-2000 07:17 PM
Craig, first off hook it back up. I'll try to simplify it's main premise. The PVC systems were designed to help evacuate crankcase vapors from the engine. This was accomplished by installing a valve that would send the vapors to the intake manifold under certain vaccum conditions only. This accomlished two things. One, to relive crankcase pressure for better sealing, and two, to burn unwanted potentialy toxic vapors in the combustion chamber instead of allowing them into the atmoshere. It was Detroits first attempt at emissions control.  Alex------------------
Alex Denysenko Co-Administrator and Moderator
Fleet of FoMoCo's too long to list!
http://superstockers.homestead.com/week.html
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steve'66
Gearhead Posts: 6602
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 11-03-2000 12:15 PM
To add to what Alex said,The pcv valve closes during high manifold vacuum conditions while the engine is idling. (otherwise you would have a big vacuum leak at idle) When the rpms increase, the manifold vacuum drops and the pcv valve opens to evacuate the fumes and pressure from the crankcase and into the intake manifold. The breather on the opposite valve cover is ok, it lets air into the crankcase while the pcv pulls air from the crankcase. The hose that originally connected to the air cleaner, served the same purpose (supplying fresh air to the crankcase). Hope this simplistic explanation helps.  SteveW
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craigber
Journeyman Posts: 78
From: Vancouver, Canada
Registered: Sep 2000
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posted 11-03-2000 12:33 PM
thanks for the info...my pcv is hooked up...it runs from the oil filler cap to the back of my carb for full manifold vacuum...on the other side (passenger) I have the K&N breather which (I assume and Steve confirms) is providing fresh filtered air to the crankcase...I think I am OK, just wanted to make sure...
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Moneymaker
Administrator Posts: 19751
From: Lyons, IL, USA
Registered: May 99
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posted 11-03-2000 01:06 PM
Thank you Steve for adding what I left out. That's one of the things that I love most about M&M. Somebody's always got your back! Alex------------------
Alex Denysenko Co-Administrator and Moderator
Fleet of FoMoCo's too long to list!
http://superstockers.homestead.com/week.html
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steve'66
Gearhead Posts: 6602
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 11-03-2000 01:10 PM
No sweat Alex, glad to help! SteveW
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460-67Stang
Gearhead Posts: 195
From: Southern Ohio, USA
Registered: Feb 2001
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posted 02-26-2001 09:28 PM
I hope it's OK to bring up an older post gang! My question is about the "PVC" setups that you see where both valve covers have hoes running directly to the exhaust pipes. Mr. Gasket sells a kit to install this. What's the purpose and advantage, if any, over stock?Thanks!
Brian
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steve'66
Gearhead Posts: 6602
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 02-26-2001 09:55 PM
Wow,Dejevu (sp?) I thought this was too familiar. LOL I see the exhaust crancase ventalation systems on rails and trailered cars at the track. I know that they use vacuum from the exhaust flow to suck the fumes from the crankcase into the hot exhaust gases. I'll step aside while the racers answer your real question. (which, I think is; where does the air (or the excess air) that is being evacuated come from?) It's a cool system for a strip only car.  SteveW
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steve'66
Gearhead Posts: 6602
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 02-26-2001 10:05 PM
Anyone remember road draft tubes? (thanks Mike!) My first car, had a draft tube connected to the crankcase, instead of a pcv valve. The suction created by air moving across the end of the tube under the car evacuated the fumes from the crankcase. Environmentally freindly, no. And it created a nice oil slick under the car if you had a ring problem. We have come a long way!SteveW (edited w/ Mike's help!) [This message has been edited by steve'66 (edited 02-26-2001).]
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kcode
Gearhead Posts: 2623
From: alvaton,ky,usa Suburb of Bowling Green, M&M #79, MCA #29208
Registered: Jun 99
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posted 02-26-2001 10:08 PM
Brian,
I think what you are describing is called the Evacupan? This is for racing only. It operates for the same purpose. What it does is to vent crankcase fumes to the exhaust headers. As the exhaust passes the port openings it creates a vacuum and "sucks" the fumes to the exhaust and out to the atmosphere. You would never pass a sniffer test if you drive it on the street with this setup. Mike
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kcode
Gearhead Posts: 2623
From: alvaton,ky,usa Suburb of Bowling Green, M&M #79, MCA #29208
Registered: Jun 99
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posted 02-26-2001 10:17 PM
Steve, I think Ford called them road draft tubes. My 63 big block had one. In fact, the tripower intake on Becks convertible has the provisions for one, a plate on the rear of the intake covers a hole for a wire mesh filter basket. Mike
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SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
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posted 02-27-2001 07:04 PM
quote:
Originally posted by steve'66:
your real question. (which, I think is; where does the air (or the excess air) that is being evacuated come from?)
Engine blowby. Combustion gases going past the piston rings. Some of the race cars now are even using vacuum pumps to suck out blowby gases. There's horsepower to be had if the pistons are not pushing against crankcase pressure on the way down the bores. ------------------
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Loc
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L Disposable Commuter
"Ford! The closer YOU look, the better WE look!"
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