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I'm still struggling to decide the best way to handle PCV on my rebuilt B20. I'm looking for the cleanest under hood experience possible, which means eliminating hoses. I've abandoned the crank case valve and hose that T's into the booster hose to the intake, and replaced that with a small K&N filter instead. It has worked well for 2500 miles (although getting black). I still have the valve cover cap with the vent pipe to the front carb filter, however. I originally left this on because of a discussion I found on Brickboard from 2008 where someone suggested that the crankcase really needed a fresh source of outside air blowing through it, and that it was best to leave a form of vacuum on one end or the other of the PCV system.
You can see where I'm going with this. I'd really like to put an old style filler cap with no vent tube on. This would allow both ends of the crankcase to vent to atmosphere, but without any flow through the engine.
So to take the debate to the next level, why do I need flow through the crankcase? The older B16's and B18's had the non vented filler cap and vent tube out the bottom without any flow assistance. Is there something about the B20 that is different? Are there health or longevity concerns if the crankcase doesn't get fresh air, or is PCV only for emissions?
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Like Phil says, it's for emmisions, however, if you block a metered amount of blowby from entering the manifold, the needles in your SU's become wrong.
--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.
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My view:
Rings are not perfect, so you get at LEAST water vapor and CO2 past them.
Probably also some gasoline.
Flow-through at a slight vacuum will carry this stuff away, making your remaining oil
somewhat less corrosive, especially when the oil reaches operating temp.
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That's a great idea. Once the oil has warmed to the extent required to turn contaminants to gas, you can encourage them out while driving. I suppose the caveat is that you may suck in similar contaminants from the other end, especially if not properly filtered.
I think you've convinced me though, I'm going to leave the top hose on.
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Most of the contaminants are manufactured in the crankcase so unless your exhaust
is blowing on your air filter that should not be too much of a problem.
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I don't have any "vacuum" venting on my B20.
I have a home made draft tube from the breather and some coiled up Scotchbright pad in the oil filler cap. To hell with emissions!
I doubt I am doing anything serious to the engine, but at this point it has over 100K on the rebuild and is smoking a little anyway. It doesn't bother me, although I can't say the same for people behind me on long downhill stretches..hee, hee!!
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I guess what I'm hoping for is for someone to be able to mount a compelling argument about why the fresh air flow through the crank case will extend the life of the engine. My rebuild only has 20K on it, so I'm a bit more concerned with the longevity of my choices.
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Hello,
The only engine longevity benefit of a proper PCV system that I can think of, is the benefits of removing escaped gases from fuel and exhaust that do get past the rings that can cause engine oil contamination requiring more frequent oil changes.
PCV also aids in performance by creating a partial vacuum inside the crankcase. Although not a significant reduction in air friction is obtained with a stock system, I know that some race specific engines use very sophisticated vacuum pumps to create high vacuum inside their crankcases to reduce air friction. I do not believe however that the emissions from these high performance vacuum systems are then combusted, but instead expelled into the atmosphere.
If you do decide to use PCV, it is important to make sure incoming air is filtered, which in most routings goes in through the breather cap/oil filler cap.
Also not always known is the fact that the mechanical style PCV valves used on B18 and carbureted B20 engines are calibrated for air volume.
We recently replaced an incorrectly sized PCV valve on a B18 engine as it was causing a high idle.
The incorrect PCV valve, probably for a V8 engine, had the correct sized hose barbs on both ends, but had too large an internal orifice and the result was a high idle.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
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It is primarily for emissions. The early caps are vented, though, just not through a hose.
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air pressure inside an engine will increase with RPMs and will escape through the the easiest location,valve cover cap or gasket ,front or rear seal or PCV which ever is easiest. So that is why we have a Positive Crankcase Ventilation valve. Pre-pcv cars had road draft tubes which extended in to the air stream under the car and at speed the air flow created a venturi effect to draw air out of the crank case. just a vent is insufficient. this excess pressure will inhibit the revolution of the crank shaft. Budget racers run the crank case vent to the exhaust pipe with an air pump check valve (to prevent reversion) to crate negative pressure in the engine. a properly designed system of some sort is required to reduce internal pressure at higher engine speeds.
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"Budget racers run the crank case vent to the exhaust pipe with an air pump check valve (to prevent reversion) to crate negative pressure in the engine."
Not this budget racer. :)
I have a hose from the flame trap to a tee at the filler cap, continuing to a (required) catch can on the right fender well. No PCV, no vacuum lines, no exhaust hookups, no nuthin'. I've never had a leak on an engine that was screwed together correctly... meaning primarily the front and rear crank seals were properly centered.
As for horsepower gains via lower crankcase pressure, I'm afraid I'd have to see proof of that; I can't believe it would be measurable on a dyno. The real gains come from keeping the oil in the sump, as opposed to splashing up against the crankshaft. To that end, most B18/B20 racers run a crank scraper, and other tweaks to the pan itself.
--
Gary L - 142E ITB race car, 73 1800ES
BlueBrick Racing Website
YouTube Racing Videos
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www.eurospares.com/suck.htm www.arcracing.blogspot.com/2008/04/crankcase-vacuum-system-cvs.html a few of many
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Wait a minute - we're talking B18/B20 engines here specifically, and hopefully at least, automotive engines in general. :) I don't think single cylinder go-kart engine sump mods are necessarily going to work on a multi-cylinder, 4 cycle, wet sump engine. (BTW - I couldn't get the first link to work, but it's probably motorcycle related?)
The hp gains claimed for the go-kart engine might be real... but that's most likely because there is only one piston, which attempts to compress the air in the crankcase on the downward stroke. A little less power may be consumed if that crankcase air is at a lower pressure at the start of downward travel. But in our 4 cylinder engines, you have 2 pistons traveling upward at the same time 2 are traveling downward; this results in zero compression (more or less) of crankcase air.
I understand that slightly lower pressure in the crankcase is beneficial with respect to leaks. But I just can't believe there's any real power gain to be had by lowering B18/B20 crankcase pressure by an inch or two of hg... and the crankcase ventilation "systems" we're talking about here (not the dry sump, vacuum-pumped variety) are going to struggle to achieve that sort of reduction in the first place.
--
Gary L - 142E ITB race car, 73 1800ES
BlueBrick Racing Website
YouTube Racing Videos
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You need low tension rings to get horspower from using vacuum in the sump.
I4's need a little extra crankcase breathing too with the pistons moving different distances at TDC & BDC.
--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.
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i was trying to say negative crankcase pressure is a good thing and there are several ways to achieve it and it is not Volvo pushrod dependent.
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crankcase pressure can also increase oil leakage, I run a single hose from a non regulated 90 degree fitting on the manifold straight back to a firewall mounted oil separator (basically a vapor filter with a collector that i can drain back into the engine, not sure why more folks dont use them..) then down behind the valve cover, around to a pcv valve and into the flame trap. i have a vent style cap with a tiny K&N breather filter on top, separate hose in similar routing for brake booster. very clean looking and easy access to valve cover.
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A picture of that cool set up would be worth a post of a thousand words here......
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