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Old 04-18-2003, 09:36 PM
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Question PCV system question?

I just responded to a pcv question in a post for Jag Daddy, and was just wondering.
Is there any reason we don't have full engine vacuum to our crankcase?
Would it help the rings or create more unwanted blowby?
Would it tend to suck in weakened or broken gasket material?
I have never seen this subject fully reviewed or explained in any depth.

[ April 19, 2003: Message edited by: M&M CUSTOM ]</p>

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Old 04-19-2003, 06:40 AM
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You do have full manifold vacuum to the crankcase M@M, only the flow rate is restricted by the PCV. The big problem is mixture leaning and contamination that varies with load if you run unrestricted evacuation of the crankcase through the intake. This is the main reason why exhaust system evacuation is so attractive, you could run it wide open as long as there was vacuum. The last thing you need is a variable flow of gases from the crankcase coming under the carb plate screwing up the mixture.

Does that make sense? <img src="confused.gif" border="0">
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Old 04-19-2003, 06:37 PM
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I still have questions about it, I agree that the pcv valve restricts the flow rate.
But where I have the main question is the open breather going to either atmospheric pressure, or the limited amount of vacuum in the air cleaner housing- which would not be full manifold vacuum.
As far as exhaust system evacuation do you mean rig up something like an A.I.R. pump to draw from the crankcase and dump to the manifolds directly thereby eliminating the need for the pcv valve and unrestricted breather.
As far as variable flow of gases from the crankcase coming under the carb plate screwing up the mixture, I would think that since the manufacturers did it that way- we could call that method a bandaid problem solver.
But still- would 15+ inches of vacuum full time to the crankcase be beneficial or detrimental to an engine?
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Old 04-19-2003, 07:08 PM
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Full vacuum pressure on the crankcase has a wonderful benefit to engine performance, more than one racecar has used a vane air type pump to draw a vacuum on the crankcase, it works very well but separating is so difficult the oil mist ends up clogging the lines. I've always thought that a small exhaust driven turbine is the best method since it is basically free power anyway.

I say build it, ring seal improves substancially but if the engine is leaking less than 5% you would see maybe 10-20 HP at most. More than one SCCA car has gone through inspection with the air pump converted to vacuum duty for some free HP.

Looks stock... :p
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Old 04-20-2003, 08:39 AM
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Clicking on your avatar shows me you are using a system similar to stock but enhanced to balance the whole system.
It looks as if you are drawing air from the air cleaner housing through both?? valve covers and sucking from the lifter valley at the rear of the intake into the carb base which earlier in this post you said causes intake mixture contamination?
If the oil mist will clog up the lines why not rig the vacuum line through a remote mount filter located to promote oil drainback when vacuum isn't being applied?
This subject is getting long and drawn out but still has yet to fully answer why we have a breather in the system, why not just apply full engine vacuum to the crankcase? Wouldn't that eliminate all running oil leaks, and only leak when parked and shut off?
4 Jaw, I could probably shoot the breeze with you for hours, but since we are on the board I will try a little more to limit myself.
(TRY- doesn't mean I'm going to refrain from posting to help me or someone else learn something new) <img src="graemlins/spank.gif" border="0" alt="[spank]" />
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Old 04-20-2003, 02:06 PM
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The system I built is not new or unusual. I just wanted to get the oil off my covers for a change. The next thing I am going to make is a fill cap with built in filter and check valve so that crankcase gas never hits atmosphere by preventing flow out of the fill cap but still allow flow when there is a vacuum. Or I could just connect the fill side to the air cleaner also and seal it off.

The amount of vacuum I could draw is limited by the amount of blowby and hose diameter at the manifold PCV, as it is now there is positive vacuum at idle and at all other speeds I have tried it at (the very scientific hand over the fill hole test :p ). I imagine as the engine wears that may change to slightly positive (80 000 miles or so), I really don't want any more crankcase contamination of the A/F than this since it varies with load and can have unpredictable results on the mixture. Generally it makes the engine run richer under load, the opposite at idle.

A nice side benefit is the oil stays cleaner and economy is improved moderately because of the increase in torque caused by a vacuum being drawn at cruise rpm. Nothing new here mind you, factory types do the exact same thing. I just like how long the PCV lasts in the new position, oil in the valve covers is extremely aerated from the valve train action and having the PCV there gets it contaminated more easily. Where it is now the clear tubing stays clean with a little white deposits when it is cold outside, in warm weather there is only a brown tinge after a couple of months of daily driving. I made the spacer also with dual ported vacuum pickups just below the throttle plates for maximum vacuum. Here's a pic;



Nothing fancy.
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Old 04-20-2003, 02:09 PM
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BTW make your posts as long as you like, this is your thread.
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Old 04-21-2003, 03:50 AM
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I know from seeing firsthand what happens to an engine when there is no pcv system in place, but that guy only changed his oil filter.
He blew enough oil smoke and mist out the garden hoses he installed to his valve cover breather fittings that he had to add oil almost every other day, he added oil when the valves rattled.
He completely lucked out to the end and when she blew, the lifter valley was a solid chunk of oil deposit crud.
So no vacuum is bad news.
Partial vacuum is the way the manufacturers did their two cents worth for the most part.
But looking on my wifes' Dodge caravan, the pcv valve is ported to vacuum but no breather is to be found anywhere?
I think it's time to experiment, and 4 Jaw Chucks' simple relocation is a good starting point.
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Old 05-05-2005, 04:30 PM
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hey boys, i've got a 64 falcon and i want to convert the breather valve to a pcv system....i was wondering if anyone had any idea of where to get a pcv converter kit. i know that california used to require an add on kit, that plugs up the breather valve and puts a PCV valve in its place, but where do i find this kit?
thanks for any light you guys can shed on it
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Old 05-05-2005, 05:22 PM
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You don't really need a kit if you are handy in the shop. All you need is a PCV valve that can be adapted to one valve cover (there are many types of threaded, grommet plug-in, hose in-line, etc., valves) and route it to full manifold vacuum, preferably in or near the plenum under the carb, and a filtered breather in the other valve cover. Any V8 valve should service any V8 engine, flow rate-wise. Ditto for a 6. In fact any valve probably will service any engine. Seal up all other openings in the crank case/valve cover zone and that's it!
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Old 05-05-2005, 09:08 PM
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Ok so you need an open filter on one valve cover or clean air piped in from the air filter. Then the pcv valve, in the other valve cover, "meters" the amount of airflow through the crankcase and into the intake manifold by using engine vacuum which is relative to engine load.

What do you do if your engine makes very little vacuum to begin with?

Larry
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Old 05-05-2005, 09:24 PM
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Well . . . frankly I have never built that healthy an engine so can't answer that definitively. PCV valves were designed for Ma-'n-Pa grocery getters that can suck the paint off a wall 50' away at idle. I still think the PCV will work on a lo-vac engine though. As long as it is continuously venting like PCVs do, it likely will be able to keep up. Maybe 2 valves in parallel? That gets to looking funky though. Just thinking out loud. Hopefully some other members with experience on hot cammed engines will comment.
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Old 05-06-2005, 06:29 AM
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pvc

Another thing to think about is the fact that you have as many cubic inches under the cylinders as you have above.......

The exhaust driven e-vac systems work excellent on the more aggresive engines. They are installed in the header with a one way valve that pulses. As the gasses pass this valve it creates a vacuum or suction and removes the unwanted gasses from the engine. by way of the valve covers/breathers..

The vacuum pumps in my opinion are a strictly race only deal. They do there job but create some other problems,,,, It's my understanding If you have one that pulls a constant 12 inches of vacuum on the engine you are going to start trashing wrist pin because of the lack of oil......

Keith
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Old 05-06-2005, 09:49 AM
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You do have full manifold vacuum to the engine evactuation.Full manifold vacuum is through the PCV.The other breather is to draw fresh air back into the motor as the PCV sucks vapors out.
Also there the exhuast evacuation like 4 jaw says,like on dragsters were they have a hose from the breather to the headers.In this the more you stand on it the more exhuast comes out creating a vacuum which sucks the vapors outta the block.
Or theres the road draft tube which is vacuum created under the car as the car moves and gets fresh air back in through the vented breather at the oil filler tube on the intake of old cars.
Or ya can just run a road draft tube and drip oil all over NYS's highways and tell um to piss off,its a 1958 ya get enough $$outta me for inspecting my other cars.
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