PCV Configuration

[Dan D.]

I would like some help and expertize in figuring out the design of 63/64 Corvette FI PCV systems.

As many of you probably know, my 57 has a 1962 327 engine and I will be running a 1963 (375) rebuilt/restored FI unit. The engine currently has a road tube. This does not play well with the 1963 FI oil tube which introduces clean air into the crankcase from the FI air meter, for the 63 PCV system. What I would like to do is convert the system to a correct 63 or 64 PCV system. This has the additional benefit of then having a sealed crankcase which would be better here in upstate NY where high humidity and long winters predominate. The humidity here seems live on 98% and never goes below 50%.

What I have learned is the PCV design was changed sometime during the 64 model year, I think as a design improvement. I am having a hard time figuring out exactly how the PCV system is configured. I plan on buying all the components from one of our supply houses, probably Corvette Central as they seem to have the most complete offering. If someone has a photo or line drawing they could post it would be a big help. I think I am pretty clear on the adapter that replaces the road tube. There was a design change to this during 64, but I believe it was a process only change.

What I am not clear on is the PCV valve, how it connects to the adapter, and where/how it gets to the vacuum source in the FI plenum. Also I believe the 63 valve is different from the 64, and the FI valve is different from passenger car as well. I believe the later design FI PCV valve has an orifice to limit the amount of vacuum usage for FI metering. The 64 oil tube is different from 63 as well, I think the 64 has an orifice. I currently have a 63 oil tube that is not in very good shape.

So I have the following questions;

Can anybody supply a photo or line drawing.
Seeing how I am starting from scratch, would I be better off using the 64 design instead of the 63 design.
What specific valve should I buy.
How does it connect to the vacuum source.

Also I will be converting the 63 port vacuum spark advance to full vacuum. Can't seem to determine where and how the line gets to the plenum. I have a B22 VAC, the engine is hydraulic, low compression, so I would expect to have sufficient engine vacuum for the FI unit.

Any help would be much appreciated.
Thanks much

-Dan-

[Duke W.]

Re: PCV Configuration

The '63/early '64 (375/375R) and late '64 (380) PCV systems are a completely different design, so if you have a 375 or 375R unit, use the '63 design. The crankcase vent outlet at the rear of the block has a rubber grommet and a steel tube that leads to a short hose that connects to a CV590C valve (same as used on other 327s) that is threaded into an adapter that threads to a tapped hole at the upper right rear side of the plenum. The '63 AIM has an illustration of this and various part houses may have online IPBs that show the parts and how they are assembled.

A tube and hoses connects the clean air source on the air meter to the oil fill tube. It sounds like you have these parts.

The ported vacuum advance on the 375 starts at the top of the air meter with a steel line and rubber hose that runs across the rear of the plenum to the VAC. I'm not sure exactly how to convert this to full time, but drilling a new hole and plugging the old hole so the vacuum advance signal port is downstream of the throttle plate under all conditions is one way. This same method can be used to convert any ported vacuum advance carburetor to full time. Same philosophy, but the details vary depending on the carburetor.

If your unit has an additional port on the rear face of the plenum you can use this for full time vacuum advance with a suitable adapter, and plug the ported line at the air meter. I think this port was used for power brakes, if installed, and blocked with a pipe plug without power brakes.

A B22 VAC provides full advance at 15", so if your normal idle speed generates about 17" or more, it will work fine. If Idle vacuum is less than 16" use a B26 12" VAC.

The other alternative is to find a PCV valve to plenum adapter that also had a 1/8" nipple for the VAC connection. Then you can run a short piece of hose from the VAC to the nipple. 380 units don't have a valve, and the plenum port that was used for the PCV valve adapter on 375 units has an adapter with a 1/8" nipple for the VAC connection.

You could probably also implement the valveless '64 design PCV system, but it has more parts, so it would probably be more expensive to implement. Also, I don't particularly care for the valveless design. Chevrolet abandoned valveless design PCV systems and began using valves again on all engines in '66, so there's a message there. I think the '63 PCV system is a better design.

Duke

[Dan D.]

Re: PCV Configuration

Thank You Duke. I appreciate your response, and it explains why I was not understanding it. I did not know that the 64 design did not have a PCV valve. I agree the 63 design is better, and that is what I am going with. My FI unit has the PB plug on the back of the plenum and I will use it for the VAC. I have all the parts scoped out and total cost is under $100. I can live with that.

The vent tube is retained only by a rubber grommet - no screw. Is this sufficient to hold it in place, or should I RTV it or something? Also I believe all CV590 PCV valves are the same - not sure what the 'C' means - sounds like a revision level.

I did not receive a photo or drawing from anybody, but I don't think I need it now. In fact, you are the only person that responded.

And I apologize for not getting back to you sooner.

-Dan-

[Duke W.]

Re: PCV Configuration

My '77 vintage P&A catalog references the valve as 6421934, CV-590, no C suffix. The number called out in the '63 AIM is 5649996. There have been many '63 PCV valve discussions mostly revolving around the configuration and detail of OE vs. replacement. In your case you just need a functionally correct replacement.

Being as how GM hasn't manufactured this part for decades, it's probably like ignition parts - same manufacturer regardless of the brand name on the box, so just buy on price and convenience. I crossed the 6421934 to BWD PCV255, and you should be able to cross it to a NAPA part no. at napononline.com or through any other brand cross reference catalog and most are online.

The early grommet at the rear of the block was a steel sleeve with a molded-in section of rubber. The sleeve pressed into the block and the outlet pipe fit into a hole in the middle of the rubber section. This was replaced in production and service by a 100 percent rubber grommet that fit snuggly into the block hole. I would install the grommet first, then the pipe with nothing but a little silicone spray lube to help get the parts properly seated.

With the grommet in the block and the pipe in the center hole the rubber gets compressed enough to form a sufficiently strong mechanical connection that also should seal well and not leak.

Duke

[Dan D.]

Re: PCV Configuration

I would like to re-visit the 63 vs 64 PCV design one more time. In thinking about it, I just wonder why they changed the design to a no-valve configuration. They did this mid-stream in 64, and making a design change such as this in the middle of a production run tells me that there was an important reason.

One thing that comes to mind is that perhaps the PCV system bleed off too much vacuum and made it marginal for the FI to meter correctly, especially with the 097 cam.

Another thought that comes to mind is perhaps it was to incorporate the flame arrester. There may have been fires.

What got me to thinking about this is I was at a local cruise show last night and there was a very, very nice 64 convertible there. This is a original FI car, black on black, PB, PS, power windows, radio delete. I looked the car over very well, in particular the fuel unit. The PCV configuration is the later version as Duke describes. It runs and starts very well with the 097 cam. Starts well that is as long as the temperature is not over 85 or 90*. The Ethanol problem again. He uses non-Ethanol from a local gas station whenever possible, but does have to use the bad stuff sometimes.

I noticed one thing with this car. The VIN # is 110053. That would make this a very early car - maybe first week production, and it has the late 64 PCV system. So I can't explain this. I'm not sure of how the VIN numbers were configured in 64, but I would think this is the 53rd car built.

Regardless, I am going with the 63 design, and should not have a vacuum problem with the mild cam I have. But if I had to I probably could incorporate an orifice somewhere in the system.

Anybody have any thoughts on this?

-Dan-

[Duke W.]

Re: PCV Configuration

I pretty sure valveless '64 PCV systems were implemented on all but L-84 at the beginning of the model year. Early L-84s were built with "recalibrated" '63 375 units and I believe they used the '63 PCV system, so L-84 did not get the valveless PCV system until the 380 unit cam on line. Maybe someone else can confirm.

The anti-backflow feature of PCV valves acts as a flame arrestor and is probably more effective than the screen used on the valveless system, which is easily damaged.

No '64 engines had 097 cams, and all '63 engines used the same valve regardless of cam. My 327/340's PCV system functioned very well - no sludge buildup over 15 years and 115K miles when I tore it down for inspection, ovehaul, and "blueprinting", and no oil ingestion including hot lapping big road racing tracks. It was a good design that did the job.

Engine families typically used the same valve in any model year regardless of the cam. Since most blowby is unburned air-fuel mixture it doesn't upset carburetor calibration very much. It's just a "controlled leak" that is compensated with slightly less throttle opening at idle and tweaking the idle mixture.

PCV systems were fairly new in the early sixties so GM was looking for a system that was both low cost and effective. None of the early SB systems provided very good ventilation to the rocker boxes. The '65 396 system drew fresh air into one rocker box and extracted the mixture of fresh air and blowby from the other side rocker box. This provided better ventilation to the entire crankcase, which includes the rocker boxes. This architecture was implemented on Corvette small blocks in '68, and I believe was implemented on the '67 350 CID Camaro engine.

Lot's of changes, then and now, are made because the responsible engineer thought he had a better design or was able to take cost out of a part or system, but it didn't always work out as originally thought.

I'm sure the Holley carbuetor was considered an "improvement" over the AFB. Go figure!

Duke

[Dan D.]

Re: PCV Configuration

Hi Duke again,

So what cam was used in 64 340s and FIs? I thought they kept the 097 in that time period. I should have asked this gentleman was cam he was running. I thought the engine was basically stock, but I did not ask him. It was pretty harry sounding, I know that. I may see him at a future cruises this year. If so I will ask him more questions. He is very friendly and likes to talk about his car.

So we can can the idea of the flame arrester being the reason for the change. Doesn't matter, I am just going with the 63 system. Will let you know how it works out.

-Dan-

[Duke W.]

Re: PCV Configuration

The last year the ...097 "Duntov" cam was used in production was '63 340/360 HP engines. The '64-'65 365/375 HP engines used the sol-called 30-30 cam, which has 19 degrees more .050" duration above the tops of the clearance ramps - about 239 vs. 220 degrees.Duke

[Dan D.]

Re: PCV Configuration

That's what I thought, but I did not think the 30-30 came out until later. It probably is a 30-30 as it sounds very wild. Apparently has enough vacuum for the FI though.

-Dan-

[Duke W.]

Re: PCV Configuration

The 30-30 cam will idle at about 900/10" with a carbuetor. FI might need another 100-200 revs for a stable idle.I recently helped John Seeley with his new 35K original mile '65 FI Coupe. John had previously set the valve clearance at my recommended .023", cold. After removing the ball bearing from the vacuum advance signal line that Bubba had installed it idled at 1000 sounding nasty as hell through the new off-road mufflers, but it started up from a dead stop without stumble with minimmal clutch slip, pulled from 1000 revs in top gear without protest, and wants to rev beyond the 6500 tach redline.Duke

[Dan D.]

Re: PCV Configuration

I'm wondering what my guy set his valves at. I could hear them 'clacking' even above the thunderous roar of the side pipes. I will ask him if I see him again.

The side pipes are not original to his car. Added by a previous owner. But he likes them, so he is going to leave them on. But he also added he likes them with the top down. With the top up they resonate.

-Dan-

[Duke W.]

Re: PCV Configuration

Valve clatter means the valves are too loose. They are being jerked off the seat and slammed back down at greater than clearance ramp velocity. Properly adjusted valves should be nearly as quiet as hydraulic lifters. Do a Google search - Hinckley Williams Valve - to get the tech paper off the Web. Make sure it's the September 2008 revison. Earlier obsolete versions are still on the Web.Duke

[Stuart F.]

Re: PCV Configuration

Dan;

Been following your thread, specially those posts between you and Duke. I may have something to add if perhaps you're not already familiar with it. In a Chevrolet TSB dated February 12, 1963, it describes a condition of accidental backfire through the carburetor during severe cold weather starts on all 63 Vettes except those with fuel injection. The last part is why I hesitated bring it up to you at all. I don't know if you can glean any value from it because I'm not familiar with the specifics of the fuelie PCV system vs. the carbureted version in 63. The backfire could result in a flame traveling from the air cleaner to the crankcase vent fresh air supply tube, igniting the fumes in the crankcase. This can result, of course, in damage to the oil pan and valve covers. The recommendation of the TSB was to install a flame arrestor screen over the vent tube in the air cleaner.

If nothing else, this may shed some light on why the engineers re-designed the 64 and on PCV systems in sort of a reverse flow, and to incorporate a flame arrestor screen.

I can speak to this with some authority as this did happen to me on my 63 340HP (L-76) back in January 1972. I had just returned to CONUS from SEA in Nov.71 and was anxious to get my Vette out of storage and on the road, even if it was in the middle of the winter. I had it stored in a garage below a restaurant in Jefferson, WI. since 1967. The garage had a very low ceiling so when my crankcase explosion occurred it was a real spectacle. Both valve covers blew off breaking away from the mounting screws, and tearing off my choke tube and fresh air hose and ricocheting off the ceiling. It wasn't pretty.

I thought it was entirely my fault due to my having the cylinders packed with Wynn's Friction Proofing and the valves collapsed. It was below zero, but I just couldn't wait. I put in new plugs and points, and re-adjusted the valves. It seemed to turn over well (I purposely cranked it for a while w/o ignition to pump out the Wynns), but just cranked too long. My thought was that I overlooked the PCV valve which may have stuck open allowing an excess of gas fumes to be drawn into the crankcase, and when the engine did fire w/ignition it blew.

It wasn't until I ran across the TSB in an addition of the NCRS 63-64 Tech Information Manual and Judging guide that I felt a little sense of reprieve. At any rate, I've had a good story to tell at car shows as to why I have replacement valve covers with the parting line through th "O". Don't know how many people believed me.

Hope this helps you think through your decision.

Stu Fox

[John H.]

Re: PCV Configuration

I noticed one thing with this car. The VIN # is 110053. That would make this a very early car - maybe first week production, and it has the late 64 PCV system.
-Dan-

Dan -

That VIN is for the 10,053rd '64 Corvette - January 29th build.

[Dan D.]

Re: PCV Configuration

Thank you. Makes more sense. I'm not familiar with mid-year VIN # assignments.

-Dan -