PCV for 73 LS4

[William M.]

Judging Manual states "Rochester equipped vehicles use a #CV736C in 1973". Is this for a big block as well?
Doctor Rebuild sent me #CV746C for my LS4 with original Carter Quadrajet and the car is running great. Would I see any change in using #CV736C, as I want to be correct for judging but don't want to re-tune if I don't have to?

[Joe L.]

Re: PCV for 73 LS4

Judging Manual states "Rochester equipped vehicles use a #CV736C in 1973". Is this for a big block as well?
Doctor Rebuild sent me #CV746C for my LS4 with original Carter Quadrajet and the car is running great. Would I see any change in using #CV736C, as I want to be correct for judging but don't want to re-tune if I don't have to?

William-----


I think that 1973 LS-4 used an AC-CV-769C. The 1973 L-82 used the CV-746C, though.

I can tell you this much: my 1969 small block originally used a CV-736C. I changed to a CV-746C and the car still ran perfectly and seemed to have a bit better oil control.

[William M.]

Re: PCV for 73 LS4

William-----


I think that 1973 LS-4 used an AC-CV-769C. The 1973 L-82 used the CV-746C, though.

I can tell you this much: my 1969 small block originally used a CV-736C. I changed to a CV-746C and the car still ran perfectly and seemed to have a bit better oil control.

A 769 was in there when I bought it. Looking in various corvette vendor catalogs I'm even more confused. Some have a single part for all 73's, others have a different part for LS4's. Can anyone else confirm what PCV should be in a 1973 LS4?

[William M.]

Re: PCV for 73 LS4

An original owner of a 73 LS4 told me he's pretty sure he's never replaced his PCV and his is a CV769C. Anyone else?

[William M.]

Re: PCV for 73 LS4

I know it's not the most exciting topic, but did I stump you guys on this one?

[Joe L.]

Re: PCV for 73 LS4

I know it's not the most exciting topic, but did I stump you guys on this one?

William-----


I don't feel stumped, at all. I'm very confident that the CV769C is the PCV valve used for 1973 L-48 and LS-4. That's the valve that GM and Delco have ALWAYS said was used, that's the valve specified in the AIM, and that's the valve on the original owner LS-4 that's been described. Is the CV769C the valve that was used on EVERY 1973 L-48 and LS-4? Possibly not. However, I believe it's the valve used on most such applications and any other valve would be "not typical of factory production".

[William M.]

Re: PCV for 73 LS4

William-----


I don't feel stumped, at all. I'm very confident that the CV769C is the PCV valve used for 1973 L-48 and LS-4. That's the valve that GM and Delco have ALWAYS said was used, that's the valve specified in the AIM, and that's the valve on the original owner LS-4 that's been described. Is the CV769C the valve that was used on EVERY 1973 L-48 and LS-4? Possibly not. However, I believe it's the valve used on most such applications and any other valve would be "not typical of factory production".

In your 1st post you said "I think that". Now that you're indicating that the 769 is in the AIM, I guess that's the one to go with (and that's the one that was on my car when I bought it).
When the car is judged, however, the JM only mentions 736. Will they deduct?

[Terry M.]

Re: PCV for 73 LS4

In your 1st post you said "I think that". Now that you're indicating that the 769 is in the AIM, I guess that's the one to go with (and that's the one that was on my car when I bought it).
When the car is judged, however, the JM only mentions 736. Will they deduct?

[Joe L.]

Re: PCV for 73 LS4

In your 1st post you said "I think that". Now that you're indicating that the 769 is in the AIM, I guess that's the one to go with (and that's the one that was on my car when I bought it).
When the car is judged, however, the JM only mentions 736. Will they deduct?

William-----


The fact that the AIM indicates the CV-769C was used for 1973 L-48 and LS-4 does not, by itself, mean that the CV-769C was used for all such applications. It's possible that things were done differently than what it says in the AIM. This is something that's actually rare, but it does happen. Also, we have no way of knowing if the sheets present in the copy of the AIM from which present-day copies were made is the definitive and complete story. So, by itself, the AIM is not proof-positive.

Also, GM and Delco parts information is not necessarily definitive or accurate. It's always possible that a part was replaced for SERVICE or that errors occurred. FAR less likely in this case, though, because I checked such information back to 1973.

The original owner, likely original valve car you described might not be definitive, either. It represents only 1 data point. It might be that it was one of only a small number of cars manufactured with the CV-769C.

However, when one puts all of the information above TOGETHER, I think it represents pretty powerful proof that the valve used "in typical factory production" for 1973 L-48 and LS-4 was the AC CV-769C. I did not have all the information I later acquired when I originally posted so that's why I used the term "I think" in that original post.

Despite all the information to the contrary, I still think it's quite possible that there were a small number of very early 1973 L-48's and LS-4's built with the AC CV-736C as a "carryover" from 1972. I'm not saying this DID happen; I'm saying it's POSSIBLE. Nevertheless, even if this did occur, that would not make the AC CV-736C "typical of factory production" for the 1973 model year.

By the way, in case anyone is wondering about this, the PRODUCTION part number for the AC CV-769C was GM #6487530. The SERVICE part number for the AC CV-769C is GM #6487532. There is usually a difference between PRODUCTION and SERVICE part numbers for PCV valves even though the AC number is the same. I do not know why this is.

[Harmon C.]

Re: PCV for 73 LS4

Judging Manual states "Rochester equipped vehicles use a #CV736C in 1973". Is this for a big block as well?
Doctor Rebuild sent me #CV746C for my LS4 with original Carter Quadrajet and the car is running great. Would I see any change in using #CV736C, as I want to be correct for judging but don't want to re-tune if I don't have to?

I have found when buying parts like you did it's the easy way out to just buy and install a 736 and hope the configeration will not get you a deduction if the new one is a little different.
If you decide to try to change the manual you need to do some research like is happening in the replies to your thread. I have got a few changes made but you should get some very original low mile cars to back up your point. Then submit it in writing for consideration to the team leader. I put a 73-454 through judging to a Duntov with a 736 and I'm not saying it was correct but as I said before it's the easy way.

[Roger S.]

Re: PCV for 73 LS4

OK what is the difference between the CV-769C and the CV-746C?
What is the GM part number for the CV-746C like that is suppose to be on my 73 L-82?

Roger?

[Joe L.]

Re: PCV for 73 LS4

OK what is the difference between the CV-769C and the CV-746C?
What is the GM part number for the CV-746C like that is suppose to be on my 73 L-82?

Roger?

Roger-----

I wish I knew what the differences were, at least with respect to the CV-736C and the CV-769C. However, I feel pretty confident that the difference involves a slightly different vacuum calibration by virtue of a change in the weight of the valve plunger or tension of the spring. Externally and fitment-wise the CV-736C, CV-746C, and CV-769C valves are the same. The question is why the need for the different vacuum calibration from most 1972 applications (CV-736C) versus 1973 (CV-769C).

However, I believe I know the reason for the difference in the CV-769C and CV-746C which is of interest to you and it does involve vacuum calibration, for sure. The CV-746C is designed to operate at the lower engine vacuum generated by engines with higher performance camshafts. The CV-746C was also used for 1970-72 LT-1 applications as well as other applications. The GM part number of the CV-746C is GM #6484525 and it's still available.

The CV-769C is kind of an interesting piece in that it was first used by GM for the 1973 model year (although there was actually one 1972 Pontiac application, too). For 1973, it was widely used across all GM car-lines. However, after 1973, it was not used again for GM cars until the 1982 model year. In between, it was used mostly for Ford products.

Also, keep in mind that there are NO GM/Delco PCV valves available today that are configured EXACTLY like the 60's and 70's originals, PRODUCTION or SERVICE. The Delco and GM part numbers are usually the same, but the parts have changed in minor ways and are rather easily discerned from originals.

[William M.]

Re: PCV for 73 LS4

A second owner of a low mile original 73 LS4 chimed in over on the Corvette Forum saying he's got the 769 also. So between these two owners, the fact that my car came with the 769, and the AIM indicating 769, I'm feeling like that's the way to go. Having said that, I'm going to stick a 736 on to comply with the JM and see what happens in Flight Judging on 9/28. I think I'll go back to my 769 afterwards and fight that battle another day.

[Roger S.]

Re: PCV for 73 LS4

The PCV valve on my '73 L-82 is this:



Does it look like what was used back in 1973?

Per the 73 AIM the L-48 and the LS4 used the same PCV valve GM P/N 6487530, as stated by Joe L above. The L-82 used P/N 6484699 which does not correspond to the 6484525.

So what is the correct GM P/N for a 73 L82 PCV Valve?

Boy, I am glad my '73 is not trying to be a top flight!

Roger

[Joe L.]

Re: PCV for 73 LS4

The PCV valve on my '73 L-82 is this:



Does it look like what was used back in 1973?

Per the 73 AIM the L-48 and the LS4 used the same PCV valve GM P/N 6487530, as stated by Joe L above. The L-82 used P/N 6484699 which does not correspond to the 6484525.

So what is the correct GM P/N for a 73 L82 PCV Valve?

Boy, I am glad my '73 is not trying to be a top flight!

Roger

Roger-----


I don't think this is the original valve that came with your car, although it is an older valve. It may have been a mid-to-late 70's replacement. For one thing, it's an AC CV-736C; your application should have used an AC CV-746C. While this valve has the "AC Spark Plug" embossment on the side which is indicative of an older valve, it also has the "greater than 4" bullet crimps on the base of the valve. I believe that original valves in 1973 were still using the "4 bullet crimp" configuration on the base. I might be wrong about this, but that's my recollection.

I believe that the GM #6484699 is the PRODUCTION part number for the AC-746C valve. GM #6484525 is the SERVICE part number for the AC-746C valve. As I mentioned previously, the PRODUCTION and SERVICE part numbers for PCV valves are usually different, although I don't know why. The AC or Delco part number is the same, though.

By the way, the PRODUCTION part number for the AC CV-736C valve was GM #6484541. The SERVICE part number for the AC CV-736C is GM #6423695 and always was.