Team Camaro Tech banner

1 - 20 of 29 Posts

·
Registered
Joined
·
2,013 Posts
Discussion Starter #1
I'm using the 70 Z28 PCV valve CV746C and my vacuum reading at the oil dipstick is 6" when it should be 1-3". I checked for a vacuum leak at the intake with soapy water and there are no bubbles and all bolts are tight.

Will a fixed orfice GM 12572717 PCV valve (don't think it's avail any longer) or one for a Chevy 409 get my reading lower. I'm suspecting this has something to do with my oil consumption. I've got 11" of vacuum at idle using a B28 can with a limiter plate on a stock dizzy with a Crane Xri module.

The 70 Z28 had a higher idle vacuum reading than 11" so the Z pcv is not good. The 69 Z/28 used the same PCV valve as the 70 did. So I need to go with a PCV that was used for the more radical cams such as the L78, 409 etc. Any suggestions?
 

·
Premium Member
Joined
·
13,705 Posts
Many of the solid-cammed engines specify the AC - CV749/769 (Fram FV178) PCV - you might want to try these first.

And :yes: the 'Fixed-Orifice' unit is often used for performance builds with good result. We are using them quit often in performance marine applications.
Don't know where you got your info, they are still available at most GM dealers as they are common for the Vortec series engines. Pace Performance had them last time I checked.
If you can't find the #12572717 unit try for an AC #CV4000C or even go to AutoZone and get the PCV1009 - they are all the same hole diameter.

If you don't get the results you wanted with those, consider a tunable unit - like this http://mewagner.com/?page_id=444

hope some of this helps
 

·
Registered
Joined
·
273 Posts
You can still get the 12572717 pcv, but you have to order hose part #12574660 to get it. PM me your email and I can send u a pic from the parts catalogue. Canadian trade price is $22.68.
 

·
Premium Member
Joined
·
7,728 Posts
The 69 Z/28 used the same PCV valve as the 70 did. So I need to go with a PCV that was used for the more radical cams such as the L78, 409 etc. Any suggestions?
I'd stay with the '69 Z/28 PCV - it had the most radical camshaft ("30-30") that Chevy ever put in a production car. :thumbsup:

:beers:
 

·
Premium Member
Joined
·
8,375 Posts
Remember back when PCV valves were a tune-up item @12K miles? Mine is still the original L78 that came with my car. Works great I might ad. Life would be good if I worked that well.;)
 

·
Registered
Joined
·
37 Posts
Sorry to highjack the thread, but I think I have the same problem.. I have a brand new sbc 427 with a lot of crankcase pressure.. Motor has about 10 miles on it, and already went through a intake gasket, I replaced it on Friday, and took it for a ride, and now its leaking out the front.. I have the pcv in the pass side valve cover and on the drivers side is just a oil cap with no breather.. I am also hearing a Pssssst noise when decelerating from about 5000 rpm..
 

·
Registered
Joined
·
2,013 Posts
Discussion Starter #14
You need a hose running from the valve cover to the breather for your fresh air.
To measure how much vacuum I have I removed the pass side tube and covered the hole with
a piece of duct tape and attached a vacuum gauge in the oil dip stick with an old straight spark
plug boot. Check reading at idle when the car is at op temp. It should be 1-3". I have 6" with the
70 Z28 PCV valve.



I've ordered a PCV that's hallow with a small hole.
 

·
Premium Member
Joined
·
8,375 Posts
Sorry to highjack the thread, but I think I have the same problem.. I have a brand new sbc 427 with a lot of crankcase pressure.. Motor has about 10 miles on it, and already went through a intake gasket, I replaced it on Friday, and took it for a ride, and now its leaking out the front.. I have the pcv in the pass side valve cover and on the drivers side is just a oil cap with no breather.. I am also hearing a Pssssst noise when decelerating from about 5000 rpm..
From one fellow hijacker to another, no problem.;)
Your system is not workable. You must redesign it.
The PCV valve MUST be at the DRIVERS valve cover. The reason is because of the direction of crankshaft rotation. And the breather (filtered) must be located at or near the passenger valve cover.
As to a manifold leak, and a PSSST, that could well be another problem.
 

·
Registered
Joined
·
5 Posts
went to autozone and got the cv1009....opened it up and there is no pintle or spring in it.....its totally empty ....wats up with that??
 

·
Premium Member
Joined
·
13,705 Posts
went to autozone and got the cv1009....opened it up and there is no pintle or spring in it.....its totally empty ....wats up with that??
What part of "Fixed" 'orifice' in the recommendation and write-up did you not understand :confused:
There is no spring-metered pintle or seat in 'fixed orifice' PCV units, just a designated hole size (based on engine needs) :thumbsup:

When I find a standard construction PCV 'Valve' is not compatible with engine performance due to vacuum characteristics I then often switch to a 'Fixed' unit.
Once an engine is broken in, and I'm sure of ring seating, I normally test for crankcase pressure at off-idle through mid-RPM levels and re-size the nominal .100" orifice if/as needed (it's usually not much) to maintain a slightly negative level.
This gives the best ring performance with very minor/to no back pressure in the crankcase for most operating levels.
 
1 - 20 of 29 Posts
Top