The intake and valve covers I took off of my sbc this weekend was set up for pcv valve and I am debating whether or not to install new pcv stuff or to just run a breather...Pros and cons of both??? TIA
pcv or breather??
- Thread starter ARCTICMUTT
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I'm not exactly sure why, but when I had my truck over at an old-head hot-rodder guy's house a couple weekends ago, he recommended I junk my PCV valve and replace it with a breather, so I did. I haven't noticed any real difference...not really sure why he recommended this though. 
I guess you get better ventilation through a breather which could result in slightly lower pressures at the top of the engine, thus reducing blow-by...but that's a 100% guess...
I guess you get better ventilation through a breather which could result in slightly lower pressures at the top of the engine, thus reducing blow-by...but that's a 100% guess...
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- #3
Thanks Rick. Can any one chime in as to why a breather over pcv? Because I was also recommended to do this by an old gear head.
I would run the PCV.
As your engine has blow by (all have some amount), the crankcase builds pressure. The PCV system or a breather system will both relieve the pressure.
With the PCV system, the intake is sucking the nasty stuff and reburning it; with the breather it's just relieving pressure.
If you have a lot of blowby, the breather is going to cake with oil and begin to drip all over the place and generally look bad.
Most of the time when I see a breather, I think "oh, the engine has so much blow by that it was filling the air cleaner with oil - it's junk".
As your engine has blow by (all have some amount), the crankcase builds pressure. The PCV system or a breather system will both relieve the pressure.
With the PCV system, the intake is sucking the nasty stuff and reburning it; with the breather it's just relieving pressure.
If you have a lot of blowby, the breather is going to cake with oil and begin to drip all over the place and generally look bad.
Most of the time when I see a breather, I think "oh, the engine has so much blow by that it was filling the air cleaner with oil - it's junk".
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- #5
I'll be running an open air filter which would mean that I would plumb the pcv valve into the intake... I have no problem running either system and if I run the breather style, cleaning up a little oil is not an issue. I am looking for the mechanical pros and cons of each...
RWBeringer said... I guess you get better ventilation through a breather which could result in slightly lower pressures at the top of the engine, thus reducing blow-by...but that's a 100% guess..
I am wondering if this is along the right lines of thinking or did the old hot rodders do this just because it simplified things and made it look "cleaner" in the engine bay when they switched to an open air filter style?
RWBeringer said... I guess you get better ventilation through a breather which could result in slightly lower pressures at the top of the engine, thus reducing blow-by...but that's a 100% guess..
I am wondering if this is along the right lines of thinking or did the old hot rodders do this just because it simplified things and made it look "cleaner" in the engine bay when they switched to an open air filter style?
Crankcase air volume changes as the pistons move up and down. With a PCV system I guess you could create a small amount of vacuum in the case that would work against the piston moving up though I'd think it was pretty minimal and not that noticeable.
That being said two of my favorite vehicles have had open road breathers (road draft tube) and no PCV valves. One was a Volvo with a B18B four cylinder - that was a fast little car and would do over 100mph. 300K on the clock and ran super clean when I sold it. The other is my Dodge 24 valve Cummins pick-up. I'd never put a PCV on either if only for simplicity sake.
cj847's comment about a breather pointing to a junk engine may be true but I've mostly used breathers when going to an aftermarket air cleaner assembly which made routing difficult. On my SBC I have a PCV valve in one valve cover and a breather on the other. Kind of a GIGO set-up
That being said two of my favorite vehicles have had open road breathers (road draft tube) and no PCV valves. One was a Volvo with a B18B four cylinder - that was a fast little car and would do over 100mph. 300K on the clock and ran super clean when I sold it. The other is my Dodge 24 valve Cummins pick-up. I'd never put a PCV on either if only for simplicity sake.
cj847's comment about a breather pointing to a junk engine may be true but I've mostly used breathers when going to an aftermarket air cleaner assembly which made routing difficult. On my SBC I have a PCV valve in one valve cover and a breather on the other. Kind of a GIGO set-up
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- #7
You just brought up a whole new question...the valve covers I took off as well as the new ones I have to go on only have the pcv/breather hole in one cover...is that going to cause any problems?
fzr400 has the right idea. Let the intake suck in as much of the nasty stuff out of the crankcase as possible. Then if there is not enough blowby it just pulls in fresh air from the other side.
Late model Jeeps use a CCV system without a PCV. The engine sucks in clean air (directly behind the air filter) if there is no excess pressure in the crankcase. The PCV is just a check valve in case the engine backfires.
There is no way that a breather reduces blowby, it can only relieve the resulting pressure build up.
As far as your one side comment - The engine is pulling a vacuum as it draws in air. The PCV system is just trying to pull this back into the engine (instead of blowing it out into the environment) If there is none to pull from the crankcase it will just pull clean air in thru the air filter.
If your engine is in good condition I'd bet my paycheck that the PCV system will have zero effect on power, mileage, or anything.
Late model Jeeps use a CCV system without a PCV. The engine sucks in clean air (directly behind the air filter) if there is no excess pressure in the crankcase. The PCV is just a check valve in case the engine backfires.
There is no way that a breather reduces blowby, it can only relieve the resulting pressure build up.
As far as your one side comment - The engine is pulling a vacuum as it draws in air. The PCV system is just trying to pull this back into the engine (instead of blowing it out into the environment) If there is none to pull from the crankcase it will just pull clean air in thru the air filter.
If your engine is in good condition I'd bet my paycheck that the PCV system will have zero effect on power, mileage, or anything.
Please accept my apologies. I just realized I used the "J" word on this forum in a non negative context. 
What I meant to say was---
If my Brother in law took a dump at my house I would prefer to pull the fumes out via a positive ventilation system vs hoping it would find it's way out via some random available breather opening.
What I meant to say was---
If my Brother in law took a dump at my house I would prefer to pull the fumes out via a positive ventilation system vs hoping it would find it's way out via some random available breather opening.
- Thread starter
- #11
Please accept my apologies. I just realized I used the "J" word on this forum in a non negative context.
What I meant to say was---
If my Brother in law took a dump at my house I would prefer to pull the fumes out via a positive ventilation system vs hoping it would find it's way out via some random available breather opening.
Lol. I have to chuckle every time I see a derogatory comment directed towards jeeps on here. I'd bet that a large majority of the guys on the forum have or had owned jeeps. I've owned 7 and the wife has 1 right now. They just don't have the land cruiser "cool factor".
Thanks everyone for the input and I definately have a better understanding of the pros/cons of each.
As it should be. Jeeps are for
and real men end up in a cruiser 
.If you have one breather hole, it's for a breather, and you'll smell it. If you cut a hole in the other side and run one breather and one PCV you'll be smell-free and have a properly vented system. The single breather is 50s/early 60s technology.