Crankcase venting ??

meracer9

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I am building a mild open:

Dyno 98 cam
4.500 rod
.040 over bore
368 tillotson on methanol

I have a ARC billet dual outlet valve cover (breather) that was given to me which I'd like to use. My question is can it be used alone or should I still run a PCV valve off the front port of the side cover?

Thanks in advance
 
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While there is the probability nothing will be gained from running the pcv valve, the same probability exists that nothing will be lost from running the same.

If this is your normal system, by all means continue that system.
 
I think that you'll want to vent the crankcase (right above the cam for an 8* or 15* mount) as well. Drill and tap 1/8"NPT (pipe thread) to install a hose barbed nipple. 3 lines to your catch can will work even better. In most of our mod/open stuff, I install two in the sidecover, and two from the valve cover. Also be sure to run them into a large enough (volume and breather) catch can -- you're going to be moving a lot of air!


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It needs a lot of venting if you go that route, the downside is your gonna blow some oil out with a heavy breathing bottom end. We used to just put up with it, add a little more oil to start. Once we sourced a good PVC valve and dyno tested it on an open we never went back. No loss of HP , and most all the oil stays in the crankcase.
 
No pumping losses .
Hopefully a better ring seal .
You are correct about the pumping loss but better ring seal is better achieved with a vacuum in the crankcase. I use a check valve in the valve cover and one in the side cover ( depending ) so on the piston downstroke pumping pressure is vented out then on the up stroke a vacuum is created within making a better ring seal. Many race car engine builders for many years have used vac systems the simplist type is using exhaust velocity in the headders connected to the valve covers , second is a vacuum pump (early ones were just smog air pumps ) so i say all engines follow the basic rules so if it works for them it will wotk for my little china
girl.
 
if you run methanol you need a vent the block to let the alcohol vapor escape from the crankcase. unlike popular belief methanol does not mix with hot oil. the vapors need a way out of your crankcase.
 
Well that's good info for sure but let me rephrase. What are the performance advantages of a pcv valve? Also how does the valve cover on a stock flathead work and are there any thing you can do to make it better? I have seen some engine builders offer a blue printed version of them and ARC sells bullet ones but Noone ever explains the benefits of either.
 
The stock one has a little valve in it . I think similar too a reed valve or at least a spring and some type of seal . Never worried too much the modifieds i used open to catch tank . The stockers i used stock . As far as blueprinted I can't say whats involed
390 fe ford and Chrysler 383 had a pvc valve the had hose ends on each end .
 
The basic premise is the piston displaces the same amount of air inside the crankcase as inside the combustion chamber. The lower the compression ratio in the crankcase, the less power loss.
This applies on every revolution of the crankshaft as opposed to every other.
The PCV valve is a one way check valve. It allows gasses to escape the crankcase, but prevents air from getting back in.
As stated, ring seal is also enhanced by the larger differential above and below the rings.
 
Seems like some are over-thinking this deal.
For a Limited Mod or Open, just do what Brian Carlson suggested and you'll be fine. I always ran two on the sidecover and two from the breather.
The ARC PCV units with the big hose were pretty trick, but I'm not sure they're even made anymore.
 
Seems like some are over-thinking this deal.
For a Limited Mod or Open, just do what Brian Carlson suggested and you'll be fine. I always ran two on the sidecover and two from the breather.
The ARC PCV units with the big hose were pretty trick, but I'm not sure they're even made anymore.
Mr. Evans I'm not over thinking, I was just curious as to the benefits. Like with Brian's statement. He explained what he had done with it but didn't really explain what was the result. Shaw so far has the best beneficial explanation and to be honest I never even thought of that being possibility but it makes sense and sounds like a great way to reduce ring flutter and blow by, correct?
 
I know the NHRA Pro Stock Bikes Love crankcase vacuum, but there in a point around 25-26 inches of mercury that some engines start having a wrist pin oiling problem. Active vacuum on our engines would work and make noticeable power gains, but implementing it is gonna' be a tough nut to crack.
 
Active vacuum on our engines would work and make noticeable power gains, but implementing it is gonna' be a tough nut to crack.
Exactly. I knew there had to be more to it. It's awesome how every part of these engines are a whole new can of worms on there own. I wonder if anyone has ever gotten it completely right.
 
The biggest hurdle will be not sucking the oil out of the engine. :)
I've never had that that issue before when installed in the valve cover ..when i vent from the side cover i make a baffle to cover over the webbing then to a barbed fitting . The check valves i use are available from Amazon (of coarse ) and are very positive sealing. The stock valve in the cover even new is in my opinion useless. At times i might get a little film in the tube from the one on the sidecover but my vent tank never gets any oil.
 
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