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Classic Mustangs Tech Forum

Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 02-01-2012   #1 (permalink)
south40 is offline PONY Member

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Default PCV Valve - Necessary or not?

I am working on my 289, and I really want to put a 1" 4 hole carb spacer on it. There was a 1/4 inch thick spacer on it previously that had a small slot for the pcv inlet. This spacer was some kind of resin and broke into 4 pieces when I removed it. I am wondering if I need this pcv valve connected or not?

Most of the carb spacers I can find do not have a pcv connection point on them. I know I could drill and tap one, but I am worried that with the 4 hole spacer I will only be tapped into one of the four holes. What will happen if I don't connect the pcv valve from the valve cover to the intake? Any thoughts on what I should do? Thanks
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Unread 02-01-2012   #2 (permalink)
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The spacer did not have the pcv valve in it it probably had a connection for a vacuum line going to the pcv in it. You can hook your pcv valve up to any vacuum port doesnt have to be on the spacer
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Unread 02-02-2012   #3 (permalink)
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I would say it's necessary to help with the blowby gases.
Just look for some other manifold vacuum source, somewhere in the carburetor.
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Unread 02-02-2012   #4 (permalink)
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Your carb SHOULD have a PCV vacuum valve on it. I know Ford used to run it's EGR system through stock aluminum spacers so this may be what you are seeing, but ERG is a separate smog-related system that re-circulates exhaust whereas PCV re-circulates crank-case gases.

Keep in mind PCV is important to the performance of your engine, the fact it drastically cuts back on emissions is a bonus. With a closed system you will be robbing yourself of horsepower, and if you don't believe me, next time you are at the race track look around at a few 9 to 8 second cars and you may notice they will have a dedicated electric vacuum motor sucking all the blowby out.
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Unread 02-02-2012   #5 (permalink)
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its not really necessary, but if you remove it you need to put a vent in the hole. like a cap that is vented. I have that on both my mustangs. the pcv is for emissions. if both valve covers are vented you will not have problems with blowby. in fact when I put my engine together initially I removed the baffles in my valve covers to make room for my roller rockers. the pcv sucked oil into the combustion caused black smoke and made it use oil. so I replaced it with the vent and have had no problems in 25,000 miles.
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Unread 02-02-2012   #6 (permalink)
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Quote:
Originally Posted by mccance View Post
its not really necessary, but if you remove it you need to put a vent in the hole. like a cap that is vented. I have that on both my mustangs. the pcv is for emissions. if both valve covers are vented you will not have problems with blowby. in fact when I put my engine together initially I removed the baffles in my valve covers to make room for my roller rockers. the pcv sucked oil into the combustion caused black smoke and made it use oil. so I replaced it with the vent and have had no problems in 25,000 miles.
Like mccance said, I forgot to mention you could easily run two breather caps in place of the PCV valve.
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Unread 02-02-2012   #7 (permalink)
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Tommay11 is correct in that cleaner emissions are a bonus of the PCV system. Many people misunderstand that this is its primary purpose. In fact, its primary function is to evacuate blow-by gases from the crankcase. This was formerly done with road draft tubes, but a PCV system is much, much more efficient. Without a way to evacuate these gases, sludge and dirt will accumulate much faster. The gases themselves are flammable, being full of unburnt hydrocarbons. Crankcase fires are even possible, though rare, when accumulated gases are subjected to enough heat and pressure. In a nutshell, the PCV system protects your engine and keeps you from having to change the oil all the time.

The spacer you describe removing sounds like a Boss 302 spacer. Stock aluminum 1" spacers with the correct PCV port are readily available. I got mine from NPD, but I'm sure they are available through many other vendors as well.
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Unread 02-02-2012   #8 (permalink)
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Hi,
Plus 1 for Joe's comments. I'm a believer in a good working PCV system for the following reasons:
It can actually add HP, be it parasitic, through reducing the internal pressures in the crank case. Meaning, on the downward stroke the piston has less pressure being exerted from beneath, thus less work.
Another benefit, with a reduction in internal pressures there is a lessened tendency for oil seepage through any seals and gaskets being challenged by pressure.
Many racers run either an evac pump system (as mentioned previously) or an evac exhaust header system. But the winner in my opinion, is the header system which utilizes the scavenging properties of exhaust to extract and reduce crankcase pressure. Thus, a free use of an existing property. No hang-on evac pumps needed.
Anyway, this is how I view it.
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Unread 02-02-2012   #9 (permalink)
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Engine blowby has to go somewhere and without a PCV system it makes a big oily mess on the outside of your engine.

Buy one of these, problem solved: 65-68 4V CARBURETOR TO INTAKE MANIFOLD SPACER
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Unread 02-02-2012   #10 (permalink)
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Do you need to have a vented cap on both valve covers or just one?? For example, I have a push in oil cap that has no breather on one, then the ford racing chrome pvc type thing on the other that has the nipple for what looks to be where the PVC hose would go.
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Unread 02-02-2012   #11 (permalink)
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first of all I agree that a pcv valve is optimal. because it does help to reduce engine wear to a certain extent by vacuuming out the products of combustion and the breather valves are somewhat less effective at that. but they do work to release the pressure and allow those gases to escape. secondly if you choose to not use the pcv, you do need the breathers on both valve covers or pressure can build up in the engine and cause leaks. third look at my engine bay on my pictures I dont see any significant oil splatter all over my firewall or on my valve covers. that may change as the engine ages and I get more blow by but I really don't have a problem with it now.
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Unread 02-03-2012   #12 (permalink)
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Quote:
Originally Posted by mccance View Post
first of all I agree that a pcv valve is optimal. because it does help to reduce engine wear to a certain extent by vacuuming out the products of combustion and the breather valves are somewhat less effective at that. but they do work to release the pressure and allow those gases to escape. secondly if you choose to not use the pcv, you do need the breathers on both valve covers or pressure can build up in the engine and cause leaks. third look at my engine bay on my pictures I dont see any significant oil splatter all over my firewall or on my valve covers. that may change as the engine ages and I get more blow by but I really don't have a problem with it now.
Friend of mine was experiencing really bad blow-by after a rebuild. He ended up using to pcv-type breathers and running the hoses to a 'catch-can' which had a breather cap on it. Otherwise his breather caps would pour out oil... real messy.

I haven't built any bada** engines so I don't have the experience to properly answer, but as for engines with a really radical cam, I think it may be tricky to find a PCV valve that would open with very little manifold vacuum. Maybe this is why you had to run the two breather caps?
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