PCV Sizes

[chevyconvert]

 
Long story short...how are pcv's sized/rated?

I noticed they have a big and small block mopar models for sale on e-bay.

Thinking mine may be too small. I just put any old one in that the auto parts place stocked.

What is correct for a 440? spring needed? or just the loose ball kind like I have ok?

Can they be too big?

is this proper for '70 440:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=011&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=320053476640&rd=1&rd=1

Experiencing leaks and strong fumes....

[70challrtse]

The one pictured in the ebay ad is correct for a big block. It is ribbed. The small block is barrel shaped - picture # 2 below.

[70challrtse]

I almost forgot, you can get them from Tom at RTs and probably for less $.

[Mopar73340]

This may be related as some have springs and some do not as you stated above. I had the problem of using the one that the books called for (with a spring) with my cam caused a whistling sound through the pcv hose and or valve at idle. I had 2 engines set up the same do this. I found a pcv valve with a weaker spring (less push to close against vaccum)  stopped the whistleing. So i guess they are rated by vacuum although I didn't find that info anywhere.

[chevyconvert]

thanks for the replies.

My concern is what if the reproduction pcv has the wrong spring rate in it?

Also, not sure why the one-way check valve is in there?

Does it vent at idle, but at high speeds the check valve closes?

this one says 440,but no ribs so it's for a small block? http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=018&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=280053586321&rd=1,1

[chevyconvert]

found some good generic info here:
http://en.wikipedia.org/wiki/PCV_valve

Good reading to fully understand the whole set-up...

[EVIL72]

This may be related as some have springs and some do not as you stated above. I had the problem of using the one that the books called for (with a spring) with my cam caused a whistling sound through the pcv hose and or valve at idle. I had 2 engines set up the same do this. I found a pcv valve with a weaker spring (less push to close against vaccum)  stopped the whistleing. So i guess they are rated by vacuum although I didn't find that info anywhere.

So that's what is causing that whistling sound I hear now and then, I also get a nasty oil leak around the pcv gromet even though I've replaced it with a new one.

[Mopar73340]

So that's what is causing that whistling sound I hear now and then, I also get a nasty oil leak around the pcv gromet even though I've replaced it with a new one.

Evil72, My theory is the stock PCV valves have a spring which is rated to work or close against lets say 16-18" of vacuum at idle. When you install a bigger cam you will have less vacuum and in my case my engines have about 10-11" inches at idle so the vacuum was not sufficient to positively close the valve and it was "fluttering" against the seat (or against the spring pressure)which was causing the noise. I just went to the local auto parts store and looked at the valves that were the same size although they had different part #'s and found that some have springs and some do not. I replaced mine with a valve with a weaker spring (less force against vacuum) to keep valve from closing at idle and the noise has stopped. One side note, when the valves are in the closed position they are not stopping the vacuum or the draw of cranckcase gas, they are just restricting part of it. So the bottom line here is the valve only restricts the air or vacuum flow at idle or when vacuum is high otherwise it is fully open.

[MEK-Dangerfield]

Thanks for the info Mopar73340. 

 It seems to me then, that these should be rated like power-valves. I know they make generic after-market pcv valves, but who knows what you are getting there.


  Mike

[chevyconvert]

ordered the "ribbed" repro big block PCV.

My existing tube size is 3/8"...is that correct for a 440 ?

[MEK-Dangerfield]

ordered the "ribbed" repro big block PCV.

My existing tube size is 3/8"...is that correct for a 440 ?

 Yes. 


  Mike

[moper]

well, not only the spring, but the oriface the ball seals on is a "metered" part. SO smaller engines have a smaller oriface. The larger the oriface, the worse the "vaccum leak" on the carb, but the more pressure it can relieve. You want the one that will do the most work, with the smallest oriface. Oil coming out of the grommet means the grommet is hard and not sealing anymore.