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PCV system questions


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34 replies to this topic

#26 spikedbeetle

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Posted 28 February 2010 - 11:13 PM

ONe side "open" w/ breater.

Other side hooked into a PCV valve installed in Manifold, or "T''d into brake booster vac line.

Point being in the end.....the only reason the air filter box is part of the PCV....is to filter air before going into the one side breater.....if you have a seperate filter on there, then the other vavle cover port get's hooked straight to the valve. No further need to tie it into the air box.


I just did some reading on PCV valves, but still have questions. This car does not need to pass emissions. There is no need for a PCV valve. So as far as crank case ventillation, should my dual breather caps work fine or should I pull crank case air through one or both carbs?

Thanks

#27 naru

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Posted 01 March 2010 - 12:46 AM

Should relieve crankcase pressure OK,but,provide no real ventilation.

Pre-PCV engines had a road draft tube extending to a slightly lower air pressure area near the bottom of the engine thereby creating airflow thru the crankcase while moving.

IMO, If one of your breathers had an outlet near the oil pan,you would have at least rudimentry ventilation.

#28 GeneralDisorder

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Posted 01 March 2010 - 04:39 AM

Yeah - a draft tube would work.

The PCV valve is less of an emissions device and more of a way to remove corrosive oil-polluting blow-by gasses from the crank-case for us that don't live in test zones. It's just a conveinent thing that takes care of the problem without the draft tube sticking down and getting in the way. In other words I do it for my oil and my engine - not for the environment. :)

GD

#29 spikedbeetle

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Posted 01 March 2010 - 11:18 PM

Okay GD. I see your point and it makes sence to remove unburned gas vapors from the crank case. I do not want to mess with my intake manifolds at this point. They are sealed and working well.

Would this plan need a pcv valve or be fine without one? Does it look a good plan? do you have any other suggestions?

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#30 Dirk

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Posted 02 March 2010 - 03:14 AM

Hey man,

I think the problem you are going to have with that is you are going to drag oil and crap into the carb. This is why the pcv system needs to be set up correctly. It should allow a positive ventilation through the engine and re burn gases without drawing to hard and sucking up oil. Hence the complex setup of different diameter pipes.

The setup you have now is much the same as mine (only smarter). The problem with this setup is as follows.

1. Gasses are not reburned and we are therefore damaging the environment.
2. There is no air flow through the crank case. This means mostly that any condesation in the crankcase will stay there and ************ up your oil. I can see this happening in my car. Over the summer the oil cap looks fine but in winter the cap and filler tube is caked in emulsified oil.
3. Catching any crap that comes out of these holes is a messy business. In my case I have ************ty soda cans that I replace now and then. In your case the filters will likely block up very quickly. If they block entirely you risk blowing an oil seal.

My plan is to salvage an intact PCV system from a doner engine and retro fit it to my engine. I would think you could do the same and just hook it up to one carb.

Cheers

Dirk

#31 GeneralDisorder

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Posted 02 March 2010 - 04:07 AM

There is little to no vacuum present at the point where you are so far above the throttle plate that you are on the inside of the air filter housing. With the throttle plate closed (max engine vacuum) you have none at all inside the air filter, and with the plates open you have almost no vacuum anywhere - much less that far away from the cylinder's and above the throttle plates.

I don't see how connecting it to the air filter housings can do much of anything helpful for the crankcase ventilation. There just is not enough vacuum signal at that point to effectively operate the system. Plus the oil mist/vapor that it would suck into the filter element and the carb on only that side (assmuing it worked well enough to do so) would be troublesome.

Basically you have two tried and true methods that can be used here - a draft tube from one of the valve cover's that sticks down by the oil pan to a low pressure area under the car, or a PCV valve. The problem you have is that your manifold's aren't shared by the carbs and as such if you install a PCV valve or port into one of them you would have to do it to the other as well to maintain the same level of vacuum loss in both. It's only a slight change but with dual carbs it could cause tuning issues.

GD

Edited by GeneralDisorder, 02 March 2010 - 04:10 AM.


#32 spikedbeetle

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Posted 02 March 2010 - 09:23 AM

So, it looks like it will be a draft tube of some kind. I read something about how in the '60's race cars used a one way valve of sorts tapped into the exhaust to suck out excess pressure. Have you heard of these? Would something like this be any better than a draft tube, and would it work on a daily driver?

#33 GeneralDisorder

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Posted 02 March 2010 - 01:29 PM

So, it looks like it will be a draft tube of some kind. I read something about how in the '60's race cars used a one way valve of sorts tapped into the exhaust to suck out excess pressure. Have you heard of these? Would something like this be any better than a draft tube, and would it work on a daily driver?


I'm not sure if that would work on a daily driver application and I would be worried simply because I would have no good way to test such a system. In theory a small opening at right angles to the flow of the exhaust would work just like a draft tube but the size and shape of the opening will make a big difference in how it operates - without being able to flow-test it you really wouldn't know if it were working correctly. Thus I would probably stick with more conventional methods just because all the math and testing has been done with them.

GD

#34 spikedbeetle

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Posted 02 March 2010 - 06:18 PM

Okay, so The original PCV valve and vacuum is best, but with what I have done to my engine, the draft tube seems to be the simplest solution. Thanks for all the opinions and help.

#35 81EA81

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Posted 28 January 2011 - 01:25 PM

The easiest way I found is using a '*' at the end of the word, so to search for 'PVC' you would search for 'PVC*' This has always worked for me! Just thought I would throw that tip in there...


thats exactly what I did, couldnt find it any other way




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