Just to update anybody who's interested.I took the top end apart today.The valley cover(sorry,pushrod cover)thats on now came off with no trouble.There are notches to clear the intake ports.Is this the way they come or did some smart guy 30 years ago cut those into it?I want to block the heat crossover when I reassemble.I have some aluminum sheet that I can use.Will this stand up to the heat or should I use tin?I should have the replacement valley cover tomorrow.Am I better to glue the gasket to the cover or the block?Any other tips appreciated.I am installing a "B" manifold and rebuilt 390 cfm Holley.Looking forward to the results of this swap.Regards,Mark

  

Does anyone know how to obtain specific specs. of available PCV valves? It appears to be a hard subject to research.



The valve supplied with my current kit (obtained from CASCO) was a FoMoCo part, which I assume was selected to suit the average T-Bird Y-block. The fact that it needed additional restriction in my case could be related to unusually high manifold vacuum (22-23", due to retarded valve timing/mild cam?) or Loadomatic complications.



It would be nice if the PCV valve for the new motor I'm building could be selected/dialed-in according to IT'S specs., with no additional restrictor used. But how?

6 VOLTS/POS. GRD. NW INDIANA

I don't think any one mentioned to change the oil fil cap. Find one with a nipple on it so it can be fed into the air cleaner. That should really help to get rid of all the fumes... Gerry

Lake Forest California  5th inf 77 Armor Div. VN 68/69

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Hello Kevink,Thanks for the info.Thats what I was going to try and use for the same reason.When I put this question in looking for some suggestions about installing PCV system I never thought it would get as many "hits" as it has.Thanks for the input from everyone.Just waiting for my replacement pan to come by mail(by the way it is called a pushrod cover in the aftermarket parts catalogue) and I will be installing this system.Regards Mark

  

I used a valve from an early 80's 302, it was made to snap into a gromet in the 302 valve cover. The end is about 3/4" and I found a gromet that would fit in the Y Block valley cover, manifold side is 3/8" hose same as the holley PCV port. I figure 302 is close to my 312 in cubic inches and works fine.

Think of the PCV valve as a variable restrictor, At high vac it is held against the spring in a part closed position. As the manifold vac drops off the spring overcomes the vac and the valve opens wider. The idea is to adjust the flow to the rate the engine produces blowby.

At idle the engine produces very little blowby and high manifold vac keeps the valve pulled back against spring restricting flow, at wide open throttle the engine produces more blowby and low manifold vac the spring overcomes vac and valve opens wider.

A fixed restrictor will work in reverse, at high vac it will flow plenty but at low vac the flow will slow down.

Daniel, I agree that the restrictor works and if you get the flow you need most of the time it is better than the road draft tube and will keep the engine cleaner. Just a thought, I do not know what valve you used but could it be connected backwards that would pull it wide open and certanly result in a lean condition.

KevinK,



This discussion has got me thinking about why my jerry-rigged PCV restrictor performs so well. I suspect it involves the original Loadomatic setup. Since the carb./distributor combo was designed for precise interaction, could it be the change in manifold vacuum conditions caused by the PCV valve confused the teapots' spark control valve, thus limiting the amount of retard upon acceleration? My worn timing chain allows running quite a bit of initial advance, and the unrestricted PCV pushed me over the edge.



Regardless, does it really matter where the blow-by goes when the throttle is wide open? Though the EPA may not agree, I would rather send it out the breather under load than into the manifold, thus diluting the mixture. The crankcase is well vacuumed 99% of the time, prolonging oil/engine life. Also, I have become (over the years), a devotee of the "if-it-ain't-broke".....philosophy, and am just grateful the restrictor fix was so successful!

6 VOLTS/POS. GRD. NW INDIANA

Hello Kevink1955,Do you happen to know what part#PCV you used or the application for it?I see your discussion regarding restrictors etc but if you think about  it there are many different PCV valves depending on application.Part of the differences would be spring pressure and I would think internal passage size depending on flow requirements for a particular engine.Does this not qualify as a restrictor?If someone is using one with too much airflow and a restrictor corrects the problem isnt it the same thing as using the correct PCV valve?Just my opinion.RegardsMark

  

The PCV port on the holley is straight manifold vac, it's not ported. While you may have plenty of flow at idle (at high Vac) I feel that at wide open throtle when vac is low (and blow by would be higher) the restrictor will cause the crankcase vapors to back out the filler cap. The PCV valve is spring loaded and opens up under low vac conditions to keep the PCV flow reletivly constant under all vac conditons. A restrictor will flow a lower flow under low vac conditions.

I agree reading plugs is the way to go, they should also all be even. Using the manifold rear port will result in uneven fuel mixtures between front and rear cylinders as the PCV flow will dilute the mixture to the rear cylinders.

Kevin,



PCV vac. source is ported spacer under the carb. Unless breather cap is restricted, oil won't pump out, even after hard/high rpm running.



Still plenty of vacuum pull through the filler tube at idle with PCV restrictor. Wouldn't main jet change be moot at low manifold vac.? Back in the day, jets were sized by reading the plugs after a full speed pull (throttle wide open=low vacuum).

6 VOLTS/POS. GRD. NW INDIANA

I also have the 390 carb and used the fitting on the carb, the fitting on the manifold is more direct to the rear cylinders and the added flow from the pcv system may cause a lean condition in the rear cylinders. My 390 is on a 312 engine and required no rejeting for the pvc.

The VW block off plate is a great idea, I was lucky and had a TBird block off plate, the bird (55-56-57) had a rear road draft tube (the valley cover you are looking for) but the block had a side opening for a road draft canister so the factory installed a block off plate.