PCV valve research...

[Roadster]

There seems to be concerns about the availability of the one unique PCV valve that is used on the LT5. Since we have a two valve system and they are a different size, it seems like it is difficult in finding one of the valve's in question.
Having a LS & RS, which is which, depending on which way you are looking at them. For our purposes and this may already be the correct way to identify them, I will refer to the LS as the driver's side and the RS as the passenger side. The RS is not a problem to purchase, but the LS appears hard to find.

When we did the plenum pull on the 94, I did not have the correct replacement for the LS, as most vendors do have a listing for the LS, but it really fits the RS. Go figure!!!
So I am still having my slight idle problem, and decided to make sure all hoses and clamps anywhere on top of the engine are secure and tight. Always do this before taking a long trip and at least every few weeks, whichever comes first. I get to the PCV valves and not only did the clamps need to be tighten, but the connector for the upper part of the PCV valves just lifted right off without much resistance. And it was a newer part. So keeping all of my old parts was a good thing to do, as I ended up reusing my original PCV upper connector. One thing that I noticed was that it was zip tied at the bottom to give a real good tight fit. I also removed the LS longer PCV valve and replaced with a regular RS one for now, and adjusted accordingly. Everything hooked and I thought maybe this is part of my idle problem, not so, but at least I addressed the loose connection. I would recommend to zip tie the bottom of the upper valve connector just to be sure you are getting a good solid connection.

I now am on a mission to find an AC Rochester CV 913 C "double hump" (as I will refer to the LS valve) for a LS replacement. Searching everywhere and researching again and again produced zero results. Finally (I hate giving up) I stumble across another "double hump" valve that has a different part number and will be here tomorrow. It is the same length which is 1 14/16" or 1 7/8" as the original, whichever you prefer and is an AC Rochester and another one (also to be delivered Wednesday) is an AC Delco. If they are correct I will then list the part number for those who are interested. But they be also getting hard to find.

The original LS PCV... CV 913 C from the 94....
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170409_132346.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170409_132346.jpg.html)

[XfireZ51]

Have you thought of "sleeving" the connector?

[Roadster]

Have you thought of "sleeving" the connector?

No, to be honest I haven't. But that is an idea to be considered. For the time being the old connector is good and tight on the valves, you actually need a slight force to lift the connector off of them. The new one as mentioned came off with ease.

[Roadster]

Latest update for those interested....
I received my first AC Delco CV895C 25095452 today and it is a perfect match for the LS (driver's side) "double hump" PCV valve. Again the original number or earlier replacement number was CV913C. With that being said, it doesn't mean that you will get the exact valve in said packaging. Some sellers have shown the actual valve in their listing and some show the regular short valve. If you can find any and intend to purchase, it would be to your benefit to make sure and check with the seller that you are getting the correct valve. I have another one coming tomorrow and hopefully it is the same item.
Here are some pics showing the valves....

My original on the right with the new valve on the left. Exact duplicate...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170411_201556.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170411_201556.jpg.html)
A pic of all 3 valves with the far right one that is used for the RS (passenger side) valve. This is the one I temporarily used for the LS for a few days. That is the short one that usually automatically ships as a LS, but also can fit the RS when purchasing LT5 LS & RS PCV valves from most vendors or suppliers. The short one is the one that was listed for the LS and shipped from a previous purchase.
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170411_202018.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170411_202018.jpg.html)
Installed on the correct sides.
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170411_204219.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170411_204219.jpg.html)
Install complete....
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170411_205143.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170411_205143.jpg.html)

[efnfast]

Why oh why would GM use two different valves????

[9T1 Red ZR1]

Tom,
Rock Auto shows V291 as crossing to the CV913C (one left in stock). I don't know if it is really correct though.

Bill

[Roadster]

Why oh why would GM use two different valves????

Don't know the answer to that one Steve, other than if you look at the configuration of the hose, you can notice where you insert the valves that it is offset. And due to that design, they needed two different length valves.
Maybe some of our LT5 experts can explain why!!!

Tom,
Rock Auto shows V291 as crossing to the CV913C (one left in stock). I don't know if it is really correct though.

Bill

Bill,
I have ordered and received from Rock Auto and other vendors the V291 valve. I have about 4 of them now and each one is the short version, not the correct one at all. And you are correct, Rock Auto, ebay sellers and such do list the V291 as a replacement for the CV913C, but from my experience, that is not the case.
It would be good if there was a way to soak the old valves in some type of solution to eliminate the build-up that they accumulate over time so that they can be used again. I don't know if that would even be possible. It would also be good if we could find a manufacture to remake these "double hump" valves. But there may not be the demand or market that they would be lookin for.
I also found a listing for a certain Ford truck that showed a pic of the "double hump" valve in their listing. But when I asked what the size in length was, it was shorter that what we needed, it was just another "short" valve.

Anxious to get today's delivery, will update later today....

[efnfast]

I pour some gasoline in them, shake 'em up a bit and let them air dry. Don't know if that is an approved procedure or not.

[Roadster]

I pour some gasoline in them, shake 'em up a bit and let them air dry. Don't know if that is an approved procedure or not.

I was thinking more of soaking them in a parts cleaner solution for an extended time, or even spraying heavily with brake kleen. My luck using gas there be a spark somewhere and something would ignite and that would not be a pretty scene.lol.... Although the brake kleen is also combustible...

[Roadster]

Just received delivery of another PCV valve and it is the correct "double hump" valve with one slight exception. And that is the length, it is a tad shorter in height (I did not measure), which you can see in the pic. It should be no problem with the install.
Another interesting observation is the packaging, the one yesterday has the new type AC logo, while the one today has the old style AC logo. Well what difference does that make you might ask!!! If you get the newer style logo package, your CV895C valve is the exact height as the "original" valve which is stamped "AC ROCHESTER", while the replacement CV895C valve is stamped "AC DELCO".
If you get the older style logo package as I did today, your valve is stamped
"AC ROCHESTER", and again is a tad shorter. It appears that the original
CV895C valves were a shorter length to begin with and may not have been intended for the LT5. Although the stamped "AC DELCO" CV895C has the longer stem by a fraction.
The "AC ROCHESTER" CV913C valve has the longer and slightly different configuration stem. Either way, no biggie, they both work but are hard to find.
Also both style logo boxes have the same part numbers, apparently "Rochester" made the early valves and AC Delco made the later ones.

CV913C on the left, today's delivery of CV895C on the right. Notice the shorter stem.
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170412_154925.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170412_154925.jpg.html)
Old style logo package...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170412_155429.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170412_155429.jpg.html)
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170412_155433.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170412_155433.jpg.html)

[Roadster]

Now to be even more :rolleyes::icon_boun
Here is a link to the AC DELCO catalog which shows 3 different PCV valves for the ZR-1 1990-1995. CV913C is shown and listed for the "Right" and #19303069 is listed for both "Left & Right".
So is the "Right" really the driver's side and the "Left" really the passenger side??? Hmmmm to be determined!!!

http://parts-catalog.acdelco.com/catalog/catalog_search.php

You will need to enter the info to get results....

[A26B]

The CV913C & CV895C may have an internal difference, specifically "crack" pressure. This could be determined by securing the valve, attaching a vacuum pump to the top connection & determining the vacuum needed to raise the valve off seat, i.e. "crack pressure.

[TealZR1]

I researched this "taller" PCV Valve a while back and could not find the exact fit. So I soaked my original in a degreaser and placed back on thinking my idle would go down to 7500 rpm. Didn't happen so pulled the plenum and found the famous hose disconnection and repaired that and thus bringing idle down to 7500! Car has 61K miles.

Really like the ZR1 car but seems to have the old Porsche 928 dilemma where parts were somewhat scarce & expensive thus driving the price down. I owned a Porsche 928 years ago and the "older" gent owner told me when I bought it from him as a young 28 year old - "you are buying a $75K Super Car for only $15K and expect your monthly payment being repairs, parts, etc to keep it running" Really fortunate we have this website and self repairing of my ZR1.
Enjoy the ZR1 performance and keep em running top notch!

:salute:

[Roadster]

The CV913C & CV895C may have an internal difference, specifically "crack" pressure. This could be determined by securing the valve, attaching a vacuum pump to the top connection & determining the vacuum needed to raise the valve off seat, i.e. "crack pressure.

Don't know if I did this correctly, but I did hook up the vacuum pump to the top "stem" connection and could not get any reading until I placed my thumb on the bottom. On both the CV913C and the short V291 valve I could get a reading as high as 23-24 in. and of course it would hold until I released my thumb. So there wasn't a way to determine when or if the valve would lift off the seat doing it the way I did. I couldn't find any other info on "crack pressure". So if you could elaborate more I could give it another try.


I researched this "taller" PCV Valve a while back and could not find the exact fit. So I soaked my original in a degreaser and placed back on thinking my idle would go down to 7500 rpm. Didn't happen so pulled the plenum and found the famous hose disconnection and repaired that and thus bringing idle down to 7500! Car has 61K miles.

Really like the ZR1 car but seems to have the old Porsche 928 dilemma where parts were somewhat scarce & expensive thus driving the price down. I owned a Porsche 928 years ago and the "older" gent owner told me when I bought it from him as a young 28 year old - "you are buying a $75K Super Car for only $15K and expect your monthly payment being repairs, parts, etc to keep it running" Really fortunate we have this website and self repairing of my ZR1.
Enjoy the ZR1 performance and keep em running top notch!

:salute:

I also gave it thought about soaking, but have read and seen others using brake kleen or carb cleaner to clean out the valve.
And are you meaning to bring down the idle to 750r's???

[A26B]

Don't know if I did this correctly, but I did hook up the vacuum pump to the top "stem" connection and could not get any reading until I placed my thumb on the bottom. On both the CV913C and the short V291 valve I could get a reading as high as 23-24 in. and of course it would hold until I released my thumb. So there wasn't a way to determine when or if the valve would lift off the seat doing it the way I did. I couldn't find any other info on "crack pressure". So if you could elaborate more I could give it another try.

Crack pressure is a terminology used in industrial safety valve testing specs, simply meaning when the valve comes off seat or begins to leak past the valve seal.

Imagine a check valve, which is the type of valve the subject PCV valve is. The PCV valve has a moveable valve that is weighted for specific conditions such as the LH LT5 valve (tall one), being one of 2 valves in the system and staged for opening under slightly different conditions from the RH valve.

If both PCV valves had the same crack pressure, subject to the same vacuum pressure and same crankcase pressure, then there would be no purpose served by having two different valves side by side in the system.

I suggested vacuum testing from the top connection over pressure testing at the bottom/inlet side because most of us own a hand vacuum tester that may be able to measure the anticipated low pressure without any special rigging.

I would approach testing in the following manner.

1. Secure the valve to prevent movement during testing. Position vertically with bottom open to atmosphere.
2. connect hand vacuum hose to top connector.
3. gradually apply vacuum in small increments & verify vacuum holding before increasing to next increment. When vacuum no longer holds, crack pressure is at point above last increment held & point leakage observed.

FYI: None of this may be achievable to a definitive end. The 895 valve may work even if it's not the same as Lotus spec'd 913 valve, just not exactly as designed. Effect may be inconsequential to the normal ZR-1 driver, and it may simply result in slightly more oil consumption that goes unnoticed.:cheers:

[Roadster]

I would approach testing in the following manner.

1. Secure the valve to prevent movement during testing. Position vertically with bottom open to atmosphere.
2. connect hand vacuum hose to top connector.
3. gradually apply vacuum in small increments & verify vacuum holding before increasing to next increment. When vacuum no longer holds, crack pressure is at point above last increment held & point leakage observed.


Thanks for the response, always good to learn something new. I did follow your steps, but before I was continuously pumping the vacuum handle which resulted in the 23-24 inch readings.
Did it again a few minutes ago exactly as stated in #3, but the gauge would not register until I closed off the bottom of the valve with my thumb. Which resulted in the same readings as last night. When I have the valve closed, the pump works fine, with the bottom opened, again not registering.

An interesting discussion.....:)

[Roadster]

Just got back from getting the 94 inspected. No emissions needed as I was just under 5000 miles....

FYI, spoke to the parts person and he verified that both CV913C & CV895C PCV valves are discontinued from GM. Then again most of you may already have known that. They just are very hard to find. Was lucky to get some 895's on the bay, but no luck on the 913's.

[Roadster]

Just received delivery today of an original NOS CV913C "double hump" PCV valve. I was notified by a member that he had found some 913 valves. I made the call, and between the two of us, we now have NOS 913's. Feeling very thankful for the info which led to the purchase. Thank you again sir, it is very much appreciated.:thumbsup::D
Unfortunately the source is now out of 913's.
In the pic, you will notice that once again the packaging is the old style AC box from many years ago. Also interesting to note is that this NOS 913 does not have "AC ROCHESTER" stamped on the valve, rather it has
"AC SPARK PLUG" stamped on it instead.


the new NOS valve is on the left, the "original" or I think original from my 94, unless it had been replaced years ago on the right....
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170420_161518.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170420_161518.jpg.html)

[Roadster]

Did a little more research and found a listing by Corvette Central for a LT1
92-96 Corvette PCV valve. Sent an email about the length and it is 1 7/8".
Which is the correct size and their current listing shows it is a CV895C, but number is not shown in the pic. Also has the application guide which is including ZR-1's.

http://www.ebay.com/itm/1992-1996-Corvette-PCV-Valve-LT1-/382057777325?vxp=mtr

Corvette Central #: 304577
Original GM #: 25095452

So another source for some 895 "double hump" valves, just in case. And I now have some extras if anyone has a problem with locating one when ready...

[-=Jeff=-]

But is the function of each game Benin the correct size the same? I have a feeling they are different despite the size


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[Roadster]

But is the function of each game Benin the correct size the same? I have a feeling they are different despite the size


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

I can't give you an answer on your thought, but if you read below part of what Jerry stated in post #15, your thought may be correct.

"Crack pressure is a terminology used in industrial safety valve testing specs, simply meaning when the valve comes off seat or begins to leak past the valve seal.

Imagine a check valve, which is the type of valve the subject PCV valve is. The PCV valve has a moveable valve that is weighted for specific conditions such as the LH LT5 valve (tall one), being one of 2 valves in the system and staged for opening under slightly different conditions from the RH valve."


Below is a pic of 3 "double hump" valves, the 1st is a NOS 913, the 2nd is the 913 from my 94 and the 3rd is an NOS 895. You will notice that the "valves" in #1 & #2 (913's) are lower than the #3 valve (895). So is there a difference in the operation of these valves as in the "crack pressure" that is mentioned? Not being an engineer, I would say, yes!!! Now is there a huge difference in the operation between the two? Again, not being an engineer, I would say that it would be so minimal that you or I wouldn't notice the difference with the exception of more oil being consumed as Jerry has also mentioned.
My main concern is that the correct size and configuration are more important, (at least to me,) than the overall operation. And as stated above, according to CC, the 895 valve is listed for the 92-96 LT1. JMO...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170426_202440.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170426_202440.jpg.html)