PCV

[c9zx]

Admittedly and ad but, seems to be accurate. http://www.engineprofessional.com/articles/EPQ315_34-44.pdf   Chuck

 

[Don C]

I agree, seems to be very accurate, matches my observations. I'm one of those that has had to guess at what valve would work best, due to lack of available data on PCV valves.

However, $129 is more than I want to spend on a PVC valve, so I guess I'll go on guessing.

 

[boilermaster]

Chuck,.

I have one on my 408 Cleveland, cannot say enough good about it.

Have even loaned mine out to a buddy to prove it out, not terribly difficult to set up.

improper pcv valves and baffling have always been one of my pet peeve's.

When we add performance to our engines the pcv flows need to change too.

Never cared too much for guessing.

Boilermaster

 

[c9zx]

Boilermaster,

   What benefits have you seen using the valve? Chuck

 

[Don C]

PCV valves are a simple and effective device, they work well and last a long time in adverse conditions. The biggest problem is lack of adjustability for low vacuum at idle conditions, resulting in too much airflow into the intake manifold. This is why so many performance engines have a couple of breathers on them, to relieve the crankcase pressures when they can't use PCV valves. It becomes impossible to adjust the carburetor enough to compensate for the additional air entering the intake manifold. It also serves as an anti-backfire device, keeping backfire flames out of the crankcase.

The idle (higher) vacuum airflow into the intake manifold is controlled by a tapered valve and a pair of springs. A weaker oulet spring allows the valve to reduce the airflow into engines with low idle vacuum.

I believe the solution is to be able to change the springs for different intake manifold vacuum conditions, or to be able to buy PCV valves with the operating conditions for them listed, thereby keeping the simplicity of the original PCV valve design.

 

[boilermaster]

Chuck,

almost 1.5'' more vacuum at warm idle, 17.5 currently and very smooth @ 800 rpms.

seeing no oil in the pcv hose or none of the very common oil mist about the breather grommets and such.

Would like to say perfect ring seal, however I have not done a leakdown test as of yet.

Might not sound like a world of difference to some, but I am ok with that.

Boilermaster

 

[c9zx]

The 1.5 in/hg increase of vacuum at idle is significant when an aggressive cam is being used. Thanks for the factual feedback. Chuck

 

[Don C]

Boilermaster, have you checked the vacuum in your crankcase? Be interesting to see if your engine has the same results as the tests.

Thanks, Don

 

[boilermaster]

Boilermaster, have you checked the vacuum in your crankcase? Be interesting to see if your engine has the same results as the tests.

Thanks, Don

Don,

I have not checked crankcase for vacuum/ pressure, perhaps I can put that on my weekend project list.

guessing I may need a gauge calibrated in inches of water.

Thinking I still have one somewhere from the days of the Fords VV carb days.

Boilermaster

 

[tony-muscle]

Interesting and timely topic. I have been thinking about this with my newly stroked engine. With EFI i may not have the issue of too much air but would like to have an optimum system.

In regards to getting higher vacuum readings, as a test, would it be the same as plugging the PCV hose and seeing if vacuum changes?

Also, as a note. The PCV hose connection i had in my engine before stroking it had a big flaw. The hose was connected to a tube that was inserted into the elbow boot to the carb. The tube was pushed and bottomed all the way into the boot which didnt allow any suction to go through, which rendered the PCV system useless. Maybe thats why i had so many leaks. I dont know if this setup is standard in our cars but it is very innefective.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[Don C]

Boilermaster, have you checked the vacuum in your crankcase? Be interesting to see if your engine has the same results as the tests.

Thanks, Don

Don,

I have not checked crankcase for vacuum/ pressure, perhaps I can put that on my weekend project list.

guessing I may need a gauge calibrated in inches of water.

Thinking I still have one somewhere from the days of the Fords VV carb days.

Boilermaster

Oh yeah, the VV carburetors, interesting concept, when they worked right they were OK, just didn't seem to work right for very long. Good thing fuel injection came along.

You can make a manometer fairly easily:

http://www.motormagic.info/vacuum.htm

 

[c9zx]

I have the Ford repair manual for the Variable Venturi carb, it is 79 pages in length and it isn't long enough. What a PITA to work on. It does save the 4300D from being the worst carb ever made. Chuck

 

[Don C]

I'll bet you couldn't put it down until you read the last page

 

[boilermaster]

I have the Ford repair manual for the Variable Venturi carb, it is 79 pages in length and it isn't long enough. What a PITA to work on. It does save the 4300D from being the worst carb ever made. Chuck

Chuck,

we used to call the vv carb the TWO STALL.

Joel

 

[c9zx]

I worked for a Lincoln/Mercury dealership in 1978. The low point for American cars. That carb, coupled with all the "emissions controls" made for a miserable automobile. A box of BBs was the most used tool in my tool box. Chuck

 

[Don C]

I used them a time or two, too, at least everything looked like it should function