Do our cars NEED a PCV valve?

patrick · Post by **patrick** » Sat May 31, 2008 3:18 am

I kinda-sorta know how a PCV valve works. It allows excess gases to ventilate from the engine's crankcase in a POSITIVE (read: one-way) fashion, and that's a good thing...

Anyhoo, I found some great-looking old-school finned cast aluminum Holley valve covers that have been sitting on my shelf since the early '90s. Since these are thicker than the normal stamped steel and don't really have any grommet provisions (other than perhaps for an oil filter cap on each side), I presume they are for racing. I want to use them on my street car.

My friend is currently painting them for me, so I don't have them with me, so I'm not sure if they have internal baffles or not. I guess my question is, for my street car, do I NEED a PCV valve (one-way ventilation) to bleed off the crankcase gases, or can I just use one of those bottom-vented breather caps (or mini-K&N looking filter pods) on both valve covers?

Also, if I do manage to retrofit a PCV valve (which I realize would need some sort of protective baffle, either integrated or bolted/welded to the valve covers), can the PCV valve HYPOTHETICALLY vent to atmosphere or MUST I hook a hose up to it to the carb to run accessories like power disc brakes, etc.? I don't have to smog my car nor have it inspected, so that's not an issue. Functionality for my power accessories is. Don't even know if that's applicable?

Thanks for all input.

73sunroofSSP · Post by **73sunroofSSP** » Sat May 31, 2008 12:17 pm

Yes it needs it. Year one has what you'll need for grommets part # FD642 and they have it in stock. It needs vacuum to operate. Are you running holley or edelbrock carter carbs? If carter it is the large center vacuum port on the front of the carb. It's the same port on holley's carb I'm unsure of the location as I haven't run holley carbs in awhile. you'll also want to baffle them somehow or you'll suck oil. Hope this helps.

patrick · Post by **patrick** » Sat May 31, 2008 2:05 pm

Thanks! I was having problems with getting the stamped steel bushings to fit in the thicker cast aluminum valve covers, so it looks like that's what I need! I presume whatever works for the Mopar cast aluminum ones will work with the Holley valve covers.

I'm a bit of a hypocrite because although I'm running these valve covers, I actually prefer Carter carbs, and am running an Edelbrock Performer Series 750cc, which I presume is same as Carter, and therefore has a center vacuum port. Thanks a lot!

Does the breather tube just hook to the air cleaner? I had an engine fire that burned up my spark plug wires, hoses, etc., so I have to do everything from scratch.

73sunroofSSP · Post by **73sunroofSSP** » Sat May 31, 2008 2:35 pm

Welcome to the club on eng fires. I had one last Aug and I'm in the process of getting mine going again. If your running the stock air cleaner the breather tube hooks on the side. Aftermarket use a vented breather instead. Yes the carter is the same as a edelbrock (which I run) as they bought the design from carter.

landon1 · Post by **landon1** » Sat May 31, 2008 4:32 pm

pcv valve connects to large port on passenger side of carb (about 8 inches away from pcv valve)

you guys with the eddy 750s lemme know how they work out for ya...i've heard just as good, if not better, performance and a lot better gas mileage -anything's pry better than the 8-10 i get with a holley, eh? it's gone up to around 12 with the electronic ignition

73sunroofSSP · Post by **73sunroofSSP** » Sat May 31, 2008 4:47 pm

landon1 wrote:pcv valve connects to large port on passenger side of carb (about 8 inches away from pcv valve)

you guys with the eddy 750s lemme know how they work out for ya...i've heard just as good, if not better, performance and a lot better gas mileage -anything's pry better than the 8-10 i get with a holley, eh? it's gone up to around 12 with the electronic ignition

I run the 600 cfm edelbrock. Don't know about gas mileage as I've never ran holleys on this car. However when I changed from a holley 2bbl to a eddy 4bbl 600cfm on a 77 cougar xr-7 w/ 302 I gained some mileage because I wasn't having to deal w blown powervalves.

patrick · Post by **patrick** » Tue Jun 03, 2008 2:35 am

Okay, I have my valve covers and they do not have any baffles. I think the easiest thing to do would be to use the Moroso PCV grommet with integral baffle and a breather grommet with integral baffle, rather than try to weld or screw on baffles. The only thing is, they state they are for "extra-tall valve covers". These old-school ribbed Holleys are certainly taller than stock, but I don't know if they'd qualify as EXTRA tall. Anyone know?

Presuming these won't work, anyone know what the diameter between the screws are for the Moroso (part # 68790) baffle? My valve covers just so happen to have two mount points under each hole, so they MAY work...

OR... I can JB Weld in the MP baffles, but what if the JB weld fails and gets into the oil pump...

1bluegtx · Post by **1bluegtx** » Tue Jun 03, 2008 3:26 pm

You actually don't NEED a pcv valve.Cars of the 50s and early 60s used a downdraft tube to vent the crankcase.I just use two open type breathers(one in each valve cover).My engine is 12.5:1 and has never had a problem blowing out main seals,valve cover or any other gasket that people will tell you will happen.I prefer not to run a pcv because it contaminates the air-fuel intake charge.

BRIAN

72RoadRunnerGTX · Post by **72RoadRunnerGTX** » Tue Jun 03, 2008 4:41 pm

The PCV system can be considered is a small metered vacuum leak. Most every carburetor or injection system manufactured since the early sixtyâ€™s has a dedicated port for this valve and is calibrated to have a valve present on it. Not sure I understand what would contaminate the air/fuel charge; blow by gas is just hydrocarbon rich air. Interesting story on itâ€™s invention, http://en.wikipedia.org/wiki/PCV_valve