PCV vs EVAC

General engine tech -- Drag Racing to Circle Track

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Re: PCV vs EVAC

Post by SpeierRacingHeads »

skinny z wrote: Tue Jan 11, 2022 4:32 pm pcv_9538c6f6c4d39b23b670c0beb763e658390c9536_4eff324de99501c6d64a2a837e4945ee1b850434.gif


Sort of like this.
Although it shows the valve is fully open at WOT.

And I'd still like to know where or if there's a breather.
I don't get it either. Here is a Stocker engine, same system.

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Re: PCV vs EVAC

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Re: PCV vs EVAC

Post by ChopperScott »

If that pcv system had a breather, it wouldn't build vacuum in the crankcase. Just like a vacuum pump, it needs a sealed engine to create vacuum.
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Re: PCV vs EVAC

Post by skinny z »

ChopperScott wrote: Tue Jan 11, 2022 5:02 pm If that pcv system had a breather, it wouldn't build vacuum in the crankcase. Just like a vacuum pump, it needs a sealed engine to create vacuum.
Now THAT'S a very valid point.
In effect the breather is whatever is getting past the rings.
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Re: PCV vs EVAC

Post by Circlotron »

Does anyone make a pcv using an IAC stepper? You could make it do whatever you like under any combination of rpm and load.
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Re: PCV vs EVAC

Post by skinny z »

I can't speak for an electric valve but I do know of this adjustable version that I had been thinking about.


DF-17-on-bench-e1483020009146.png


http://mewagner.com/?p=444
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Re: PCV vs EVAC

Post by rfoll »

skinny z wrote: Tue Jan 11, 2022 5:05 pm
ChopperScott wrote: Tue Jan 11, 2022 5:02 pm If that pcv system had a breather, it wouldn't build vacuum in the crankcase. Just like a vacuum pump, it needs a sealed engine to create vacuum.
Now THAT'S a very valid point.
In effect the breather is whatever is getting past the rings.
That is what I was saying in my post. If the engine develops a problem, the 2 pcv valves would likely be unable to keep up and would pop out.
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Re: PCV vs EVAC

Post by PRH »

The pan evac isn’t legal in Stock.
Not sure about SS.
Somewhat handy with a die grinder.
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Re: PCV vs EVAC

Post by 6.50camaro »

Smoke and Mirrors? Has anyone seen a Stock or Super Stock car running that set up. Just asking .
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Re: PCV vs EVAC

Post by SpeierRacingHeads »

FJ Smith and both.

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Re: PCV vs EVAC

Post by HQM383 »

F-BIRD'88 wrote: Tue Jan 11, 2022 4:18 pm
HQM383 wrote: Tue Jan 11, 2022 2:58 pm
ChopperScott wrote: Tue Jan 11, 2022 2:52 pm If it’s drag only, with no mufflers, I’d go with exhaust evacuation…

4E28BEC4-D43F-4785-88B7-F86955E1F79C.jpeg
Exactly. Pcv is useless on a drag car as it is closed at WOT.
The PCV valve does not Close @WOT. But there is a anti back fire safety valve function to stop a blow back crankcase fire. The flow pindle does move to the low vaccuum position against the pindle valve spring inside.
The low vaccum position creates more flow thru when manifold vaccuum is low (wot)
SpeierRacingHeads wrote: Tue Jan 11, 2022 3:43 pm If it's useless, why does all the $45,000 Patterson Super Stock engines run dual PCV?
Touché, I was wrong with my general statement :oops:. A correctly calibrated pcv is open at WOT. Most OEM pcv will have a spring strong enough to close the valve at WOT with a modified engine that's pulling less vac than the pcv was calibrated for.

A proper sealed system uses the pcv on one rocker cover and on the other a sealed filler cap (not totally necessary) and the other end of the same rocker cover an open tube that goes to the base of the air cleaner for fresh air through the system. Sealed and gasses always recirculating. As someone said a breather would limit amount of vacuum in the crankcase. Something seems incomplete in those photos to recirculate air and not suck gaskets in unless the cap has some ventilation?
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Re: PCV vs EVAC

Post by Joe Kraemer »

I do know that a header evac system set up properly can pull 7-8" of vacuum.
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Re: PCV vs EVAC

Post by F-BIRD'88 »

There are also fixed orifice type pcv valves.
There is only a anti backfire one way check valve inside and a flow orifice. I believe chev LS truck engines have this type pcv
Would be interesting to see the details of the function and baffling of the E vac/Pcv breather system on that FJ Smith Super Stock.
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Re: PCV vs EVAC

Post by barnym17 »

The setup Bill jenkins used was intake vacuum with oil seperators plus an exhaust vacuum system.It was detailed in his book on small block chevy.Using this setup he was able to pull vacuum on the crankcase at both idle low throttle conditions and wide open going down the track.According to him this setup pulled enough vacuum he had to run the crank seals backwards for sealing.
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Re: PCV vs EVAC

Post by steve cowan »

Unless you own or build these style of engines I doubt we will see inside of anything :D
My opinion is we should be thinking of what they are trying to achieve having to use that type of crankcase ventilation.
Those short blocks are more than likely turned over with a inch/LB torque wrench.
Blowby would be very low,maybe the low manifold vacuum at high rpm with that setup is worth a couple of hp and hundredths at the track.
I am sure Vortecpro put a video up a few years ago where he is spinning a short block over one handed,he must be very strong :lol:
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