PCV Valve

[Joe C.]

What is the current AC replacement for the CV726C? Is it the CV679, which cross references to Purolator PV679? Was this valve, as used for 1966-67 Corvettes piped directly to manifold vacuum, or was there a orifice or limiting valve of some sort employed.

Thanks in advance.
Joe

[Joe L.]

Re: PCV Valve

What is the current AC replacement for the CV726C? Is it the CV679, which cross references to Purolator PV679? Was this valve, as used for 1966-67 Corvettes piped directly to manifold vacuum, or was there a orifice or limiting valve of some sort employed.

Thanks in advance.
Joe

Joe-----


There is no current GM or AC Delco replacement for the CV 726C. It was discontinued without supercession about 20 years ago.

Addendum: Also, the CV-679 is a completely different configuration valve. The CV 726C has threads on one end and a hose barb on the other. The CV-679 has hose barbs on both ends. It's possible that it would be usable with significant modifications to the PCV system but it was not cataloged by GM as a replacement for the CV 726C.

[Timothy B.]

Re: PCV Valve

Joe, On my 67 300 HP car it's piped directly to manifold vacuum.

[John H.]

Re: PCV Valve

Joe, On my 67 300 HP car it's piped directly to manifold vacuum.

Yup, same here.

[Joe L.]

Re: PCV Valve

What is the current AC replacement for the CV726C? Is it the CV679, which cross references to Purolator PV679? Was this valve, as used for 1966-67 Corvettes piped directly to manifold vacuum, or was there a orifice or limiting valve of some sort employed.

Thanks in advance.
Joe

Joe-----


I did a little further checking. As I mentioned, the AC CV 726C was discontinued without supercession from both the GM and Delco parts systems about 20 years ago. However, "sometime since" the CV 679C has been cataloged in the Delco parts system as having application to 1966-68 Corvettes with 327. I believe this is an error that's not been corrected.

[Joe C.]

Re: PCV Valve

All,

Thanks for helping. What I'm planning on doing is this:

I'm in process of "upgrading" my 1965 L76 with some more stout internals, and dressing it with headers, a 14044836 (service replacement LT1/Z28) intake, a 750 CFM Quick Fuel Q750 carburetor, a 1966/67 SBC Corvette style drop base-open element air cleaner (all of which will fit under the smallblock hood). All other externals, including heads, valve covers, pulleys/belts/idler/pumps/torsional damper will remain as original.
I will fit this engine with a PCV valve, and eliminate the .090 fixed orifice which was original setup with the 2818. I will use the 1965 oil fill tube, and the AC 679C, which APPEARS to be identical to the CV726C, except that it has rubber hose fitting instead of pipe threads on the upstream side. This will enable me to fit it in-line, in the same place as the CV726C, but using my 1965 type oil fill tube.

I have written to GM, and asked whether the internal orifice and pintle/spring setup is the same, or similar to that used in the CV726C, and I'm waiting for an answer. Meanwhile, I temporarily swapped the 679C into my '85 Corvette, and it idled same and road tested the same as it did with its correct, original PCV valve.............not very scientific, but, a start.

The original CV726C can be had for anywhere between 18 and 40 bucks, while they last.

Joe

[Timothy B.]

Re: PCV Valve

So you are using the original breather tube at the rear of the engine to complete circulation back in. Seems like PCV air restriction can be a tuning tool for idle in some instances.

[Joe C.]

Re: PCV Valve

So you are using the original breather tube at the rear of the engine to complete circulation back in. Seems like PCV air restriction can be a tuning tool for idle in some instances.

That's right, and that's right. The flow direction and path will be the same as 1964-67 SBC Corvette. I'm not sure about this, but thinking that the 1963 flow path is different, and of course so is '68-up.
Too bad one can't specify calibration for PCV valves. With the myriad choices among them, ya gotta know that there are subtle nuances in their calibration. One of the great, unsolved mysteries of engine design. Choosing the "best" PCV valve for each application is a lot like buying a fedora hat (not that I would know, you unnerstand)...if it feels right............

When this project nears completion, I'll fine tune everything with my Zeitronix wideband air/fuel ratio meter:

http://www.zeitronix.com/Products/zt2/zt2.htm

Both header collectors will be fitted with bungs for the O2 sensor.

[Timothy B.]

Re: PCV Valve

The 63 path os opposite but I don't think it makes any difference, pcv to back of carburetor from rear of engine and filtered air to front of manifold. Good idea with the bung for sensor.

Joe, Is that part # a service replacement LT1 manifold??

[Clem Z.]

Re: PCV Valve

be careful with PCV valves because i know of a case where a guy overhauled his engine because it used oil after the overhaul it still used the same amount oil and it turned out to be the incorrect PCV valve. this was a engine where the PCV valve mounter directly into the rocker cover. installed the correct GM valve and the oil problem went away

[Joe C.]

Re: PCV Valve

The 63 path os opposite but I don't think it makes any difference, pcv to back of carburetor from rear of engine and filtered air to front of manifold. Good idea with the bung for sensor.

Joe, Is that part # a service replacement LT1 manifold??

Yes, it is. It is a replacement for 3972110 and 3972116, Z28/LT1.
These originals are getting VERY expensive. I found a real nice manifold last year after quite a bit of looking, at a very good price. The boss for the front oil fill tube exists, but must be bored to accept tube. There are other service replacement numbers which were made with the front hole bored and fitted with a Dorman plug.

Other casting numbers:

3917610...........67-68 Z28
3932472...........69 Z28
3972110...........70 Z28/LT1
3972116...........replacement for 3972110
14044836.........replacement for 3972116

They are listed in descending order of going price.
There are differences among them as to the config of the oil fill tube bore, or boss, t-stat housing location, temp sensor and heater hose taps.

Joe

[Clem Z.]

Re: PCV Valve

Yes, it is. It is a replacement for 3972110 and 3972116, Z28/LT1.
These originals are getting VERY expensive. I found a real nice manifold last year after quite a bit of looking, at a very good price. The boss for the front oil fill tube exists, but must be bored to accept tube. There are other service replacement numbers which were made with the front hole bored and plugged with a Dorman plug.

Other casting numbers:

3917610...........67-68 Z28
3932472...........69 Z28
3972110...........70 Z28/LT1
3972116...........replacement for 3972110
14044836.........replacement for 3972116

They are listed in descending order of going price.

Joe

how about hood clearance as i believe the original 68-69 Z manifolds were taller than the corvette manifolds.

[Don C.]

Re: PCV Valve

Hi Joe

FWIW, when I switched to a Pro-Systems carb on my 'upgraded' 1965 L79, I replicated the PCV fixed orifice by drilling a .090 hole in a short piece of hardwood dowel (could have used a piece of steel or aluminum) of a slightly larger OD than the ID of the PCV hose. I forced this improvised piece into the end of the hose nearest the oil fill tube and presto I have a 'PCV valve'. Seems to work fine and I can check it anytime for blockage by removing the hose and inserting the drill. No problems in two years - that would be a grand total of about 2000 miles.
For tuning, a number of such 'expensive' pieces can be fabricated using different drill sizes.

Don

[Joe C.]

Re: PCV Valve

how about hood clearance as i believe the original 68-69 Z manifolds were taller than the corvette manifolds.

Clem,

I measured hood clearance with the Z28 manifold topped with the 2818 and the 1965 style air cleaner. All clearances closed up by slightly less than 7/16" when hood closed with dum-dum plugs on top of all 4 corners of air cleaner. The tightest clearance is on the right-outboard edge of the air cleaner, which went from 15/16" to 1/2".

The Holley center hung float, 750 double pumper is same height as the 2818. The 66-67 style drop base air cleaner is better because it's 3" high as opposed to 2", and is open element for much lower restriction. I am assuming that the height of the late style SBC air cleaner, although it is much better and 3" tall, will fit under a smallblock hood. If not, I'll likely add shims to the body mounts.

Joe

[Joe C.]

Re: PCV Valve

Hi Joe

FWIW, when I switched to a Pro-Systems carb on my 'upgraded' 1965 L79, I replicated the PCV fixed orifice by drilling a .090 hole in a short piece of hardwood dowel (could have used a piece of steel or aluminum) of a slightly larger OD than the ID of the PCV hose. I forced this improvised piece into the end of the hose nearest the oil fill tube and presto I have a 'PCV valve'. Seems to work fine and I can check it anytime for blockage by removing the hose and inserting the drill. No problems in two years - that would be a grand total of about 2000 miles.
For tuning, a number of such 'expensive' pieces can be fabricated using different drill sizes.

Don

Hi Don,

How are you progressing on your rocker arm ratio research?

I have ported my (non - "X") 461 heads and have gotten all intake ports safely, to 195cc!!!!

I want to eliminate the fixed orifice, so as to have better scavenging at lower manifold vacuums. At very low manifold vacuum, the .090 orifice limits ventilation of the crankcase.

Joe