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Running dual PCV valves?

uh, guys, the breather is there to let air into the engine,, the tube to above the TBI is letting in filtered air(the tube is called the "PCV air make-up tube" in engineer speak), and too much vac in the crank case is bad, same with too much pressure, it with move gaskets(suck in or blow out) causing large oil leaks, 2 PCV valves are ok if you still have a breather to let air in (p.s., oil coming out the breather when the PCV valve/vac is good means you have too much blow-by, most likely caused by worn piston rings)
 
Thats what I think too... If your breather is soaked with oil, you probably have a plugged up PVC, or you don't have enough vacuum to it... breather is intake...
 
Thanks for all the comments fellas.

My old tired 350 had a weak cylinder for sure so I now know that this was the cause of my breather getting oil soked and making a mess. I didn't want this to happen on the 454 I am putting in. Now that I know the cause of the mess I can expect the 454 to stay clean with a breather.
My 454 is completly rebuilt so I think I will just run one PCV and get a breather for the other side.
What kinda of breather should I get?
Thanks again for all the comments:D
Burt
 
You can use the stock "bowtie" air breather filter that goes in the air cleaner--It will fit right into the rubber grommet on the valve cover(passenger side)--on a few old motor I had with excessive blow by I used a long peice of 3/4 heater hose from the valva cover and stuck the bowtie filter in the other end,and ran it under the cab far back enough to keep fumes out of the cab..I had to do this when the air cleaner was starting to fill with oil,and clogging the filter....the bowtie is where the air is supposed to enter the engine,but as the rings wear and allow too much blowby,the airflow reverses and the suction from the air rushing down the carb throat pulls the blowby down into the intake,and it brings oil with it,that puddles up on the air cleaner housings base--

I'm not so sure 2 PCV valves would be any better than one--a single one with a higher rate of flow might be better--using 2 tee'd together would probably result in each getting only half the flow----and another PCV is another vacuum leak--might lean the fuel air mixture too much.....might take some experimenting to see if it actually helps....
 
I was reading Hot Rod magazine today and spotted a little article. In it they talked about a Ford Vaccum pump. I guess it was used on Cobras to increase manifold vaccum, anyway they routed it to the breather on a motor and it pulled 5 inches of vacuum. It was good for a 5HP increase in power. They noted it would allow lower tension rings to be run since the issue of blow by wouldn't really be there. They also said they tested a BBC with a belt driven vacuum pump that pulled between 8 and 15 inches of vacuum and was good for more power(no actual numbers, but they said it was a dyno test just for that issue).
 
Sounds great in a mag, but crappy in real life. I wouldn't run low tension oil rings in anything but a race car.

That said, the japs have been doing it for years to try to increase power in their tiny engines.
 
Burt, you must have at least one PCV valve and one breather that connects to the air cleaner for the system to work properly. An engine which is new or in your case rebuilt, will have very little blowby. Blowby is combustion gases that pass the rings when combustion takes place and enters the crankcase. Every engine will have blowby but as the engine gets older and the pistons, rings and cylinders start to wear you will get more blowby. The only way for the system to work properly is to have a source of suction (your engine is a vacuum pump) which is metered (PCV valve) and has a one way valve in it and it needs to be attached to one of your valve covers, you also need to have fresh air entering the crankcase so you don't build negative pressure which would suck oil into the PCV system.
 
The more vacuum or less positive pressure you put in your crankcase will raise your horsepower by helping the rings seal better and in turn giving you better compression. This is why race cars use vacuum pumps.
 
If you choose to put in two PCV valves, I'd put both of them on one valve cover. Otherwise you're never putting "fresh" air in the crankcase. When on opposite valve covers they'll have a tendancy to just evacuate that one valve cover.
 
CyberSniper said:
If you choose to put in two PCV valves, I'd put both of them on one valve cover. Otherwise you're never putting "fresh" air in the crankcase. When on opposite valve covers they'll have a tendancy to just evacuate that one valve cover.
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That's what I was thinking. Should'nt you hav the PCV on one valve cover and the breather on the other.

BTW mine has no PCV ,been keeping a close eye on this thread so I can get one on it properly.
 
Greg72 said:
What the heck do I know....? I can barely even get emoticons to work in my posts these days! :grin:
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How the heck do you do that anyway???
 
Doh!

Ok, I got it now!!:grin: :xmas: :pimp: :woot: :truck: What fun! Thought we'd lost these!
little things please little minds!:D
 
its not good to have no PCV

I hope you are keeping the oil changed frequently--without a PCV valve the oil will sludge up rather quickly,because the water vapor in the crankcase wont get purged out,and condensation will build up under the valve covers and turn your oil into mayonaise---also the carb is jetted to compensate for the vacuum leak the PCV valve causes--not having one will richen the mixture,and it will be "sooty",lowering mileage and performance some...:crazy:
 
Be careful with that, if you're getting enough blow by to soak the filter with oil it can drip out of a valve cover breather and onto the exhaust manifold, causing nasty smelling smoke that can make driving it unpleasant to say the least. This is experience talking. I'd advise to put a pcv valve in that hole with the guts taken out and run a hose to a remote location with a filter on it, so that if it does drip, though the extra lenght should help prevent that, you don't have to deal with the smoke and fire hazard.
 
Thanks everyone, just to clarify this is for my brand new rebuilt 454. My old tired 350 i put to rest was the engine with excessive blow-by causing the crank pressure to go up and oil pukeing out the front seal & breather. I am all too familiar with the smell/smoke. I smoked out the entiere state of Utah on my way back from Moab. I went thru probly 10qts of oil until My good buddy Tori suggested adding a second PCV to releave the excessive crank pressure. This worked like a charm.

I will keep it down to one PCV and add a breather tube to my air cleaner. Wait if I put the breather to the air cleaner will the intake create a vacume in the breather tube...oh heck I did it again..done CornFuzed me self again:confused:
 
blazerpunk said:
That's what I was thinking. Should'nt you hav the PCV on one valve cover and the breather on the other.
Click to expand...
I asked my engine builder that exact question, and he said yes they definitely have to be on opposite sides.
 
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