1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

[R N.]

Hello Everyone,

I've been reading lots in the archives about the use of the CV 691 and the CV 736 PCV valve for the 1966 L72 BB Corvette. From what I've read, the early cars had the CV 691 and at some point (Mid-production ?) production switched to the CV 736 valve.

I'm trying to determine what PCV valve I should have - my car is VIN 17534 built March 25th. Has it been decided when the switch over occurred? What valve should I have?

I asked Matt Lewis here on the board about his survivor car as it's close to mine (build a month later) and he has the CV 736, so I could assume I should have the same, BUT I would really like to know for sure what the correct valve is for my build date.

Thanks in advance to everyone who chimes in.

[Ronald L.]

Re: 1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

Kurt -

The service parts books alone are sufficient evidence to tell the doubters the 390 HP 427 cars used the 691 valve from inception through 1968. 1969 the applications were combined.

425HP cars started getting the 736 valve as soon as they could engineer it due to a functional issue with the 427 pcv system. Change over was a little faster than most probably want to believe, depending upon how much they paid for the wrong rare part, but documents show December, could have been before that, could have been January.

Now if you are chasing the 736 original configuration valve , be aware that there are fake 736 valves on the market - sold as originals - untested - use at your own risk.

Labels - another controversy - that is soon to be erased.

Let's just start here - You won't find labels in 67 AIMS, 67 parts books nor on any AC SP valve mid year 1966 and later so hard to put something on a car that did not exist, and yes, the repro wanabe labels are a joke, none are even close, starting with the construction, configuration etc.

[R N.]

Re: 1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

Hello Ron,

Thanks for your insight to the valve. Can you share more information about the pcv labels - whats correct and will you be reproducing them?

[Michael S.]

Re: 1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

Kurt -

The service parts books alone are sufficient evidence to tell the doubters the 390 HP 427 cars used the 691 valve from inception through 1968. 1969 the applications were combined.

425HP cars started getting the 736 valve as soon as they could engineer it due to a functional issue with the 427 pcv system. Change over was a little faster than most probably want to believe, depending upon how much they paid for the wrong rare part, but documents show December, could have been before that, could have been January.

Now if you are chasing the 736 original configuration valve , be aware that there are fake 736 valves on the market - sold as originals - untested - use at your own risk.

Labels - another controversy - that is soon to be erased.

Let's just start here - You won't find labels in 67 AIMS, 67 parts books nor on any AC SP valve mid year 1966 and later so hard to put something on a car that did not exist, and yes, the repro wanabe labels are a joke, none are even close, starting with the construction, configuration etc.

Ron,
This is a great discussion. (Kurt I don't want to break into your thread but I have to ask a couple questions of Ron.)
1. When the 390 hp cars were converted to 400 hp cars, did they retain the original 691 valve?
2. What valve would be correct for a 400 hp '67 built in November 23-25 of '66?

[Ronald L.]

Re: 1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

The segregation was the difference between Special Hi Performance and base engine so yes the base 400HP with hyd cam stayed with 691.

Now as we had indicated in another thread, the question on labels, we can say that by June 66 labels weren't on the valves. There are some that question if they were ever on the factory installed valves at all, and that's an interesting discussion, hard to answer as a pcv change is an easy part to massage on a survivor car.

PCV valve construction is the same as 66 in that the new metal forming process was not yet developed that would be seen starting on 1968 model year valves.

Labels in the works with real materials.

[R N.]

Re: 1966 L72 BB CV 691 and CV 736 PCV valve (Again........)

The segregation was the difference between Special Hi Performance and base engine so yes the base 400HP with hyd cam stayed with 691.

Now as we had indicated in another thread, the question on labels, we can say that by June 66 labels weren't on the valves. There are some that question if they were ever on the factory installed valves at all, and that's an interesting discussion, hard to answer as a pcv change is an easy part to massage on a survivor car.

PCV valve construction is the same as 66 in that the new metal forming process was not yet developed that would be seen starting on 1968 model year valves.

Labels in the works with real materials.

Ron ---

Keep us posted about the labels please....