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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 09-13-2010   #1 (permalink)
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Default 1966 Mustang-PCV valve delete

My 66 is a weekend driver these days and I am thinking about pulling the pcv valve and replacing it with a breather cap. It seems to me that with the tiny amount of driving time it gets there is little effect on the environment. Besides its not a sealed system anyway with a breather on the oil filler. I am thinking that it would be worth it to keep the oil blow by out of the intake and keep the engine a little neater without another hose in there. Are there any negatives to this?
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Unread 09-13-2010   #2 (permalink)
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Absolutely. The PCV system isn't there to help keep the environment clean, despite what all the tree-huggers would have you believe. It's there to keep your crankcase clean. I'd much rather put up with one hose in my engine bay than have to change my oil every 1000 miles. Under the right conditions, blow-by gases in the crankcase can actually catch fire if they are not properly evacuated. Cleaner emissions are just a free bonus, not the primary purpose.
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Unread 09-13-2010   #3 (permalink)
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Hello. Ditto. The reason that the oil filler cap is vented is to provide a point of entry for fresh air. You have the pcv valve sucking gases out of the crankcase. If you don't have a place for air to come in, the pcv valve can't pull anything out. Air goes in through the oil filler cap, not out.
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Unread 09-13-2010   #4 (permalink)
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I think you don't understand the physics of a road draft tube.

A PCV system draws gases SLOWLY out of the crankcase, through the carb and burns them eventually. Its purpose IS to keep that stuff out of the atmosphere. Why else did it only appear on emission controlled cars? On 60s Fords it was sometimes a $5 option but later became mandatory by first CA and then the feds.

A road draft tube hangs down and is designed such that the moving air flowing past it causes a partial vacuum (exactly the same way that a carb venturi works) that sucks the gases out much more quickly since there is no flow restriction as in the PCV valve, etc. Some systems have additional restriction after the valve to further impede gas flow so as not to flood the intake system with blowby. The crankcase will be much CLEANER with a road draft tube than a PCV. If anything, oil change intervals would be LONGER using a road draft tube than a PCV. I doubt it actually makes any difference for oil changes.

If the engine has blowby (which they all do to some extent) then it has to go somewhere. Replacing the PCV hose with a breather means its going to make an oily mess on your valve cover. The road draft tube would dump it into the air below the engine. Doing away with the PCV will not help performance in the least so I fail to see a reason to work very hard to get rid of it. If blowby is so bad that its plugging the PCV, etc., its time for an engine overhaul. Smoky old cars give the hobby a bad name and give those tree-huggers an excuse to want to work harder to make old cars illegal which some of them already would like to do.
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Unread 09-13-2010   #5 (permalink)
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I wasn't arguing against a road draft tube, but rather the elimination of any ventilation device at all. I've never had a road draft tube, but the people I know that did have them say they didn't really work all that well. If the OP wants a road draft tube rather than a PCV, it's still 100% better than nothing.
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Unread 09-13-2010   #6 (permalink)
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Well a RD tube will actually go against my original intention wich was simply to clean up the engine bay. I was just thinking not being a sealed system like modern cars the start up gasses are not being captured that well anyway and id cut out what oil does run back into the intake as well. However if its really going to be that negative then its not worth the effort. Glad I asked first.
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Unread 09-13-2010   #7 (permalink)
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Just to set you more at ease, any oil that goes into the intake is immediately incinerated in the 600+ degree combustion, so it does no harm to any of your engine components. It never has a chance to settle in and gum anything up.
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