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tips, technology, tools and techniques related to vehicle driveline components

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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 26, 2014 11:29AM

As distinguished from American PCV, the British system puts the engine crankcase under engine vacuum. This is done by running a relatively large tube from a breather to the manifold and then providing an orifice to allow metered and filtered air into the crankcase. The theory is good, it's a passive system that can handle great quantities of blowby easily, but any air leaks in the crankcase will increase idle speed, perhaps uncontrollably.

I question just how good the crankcase seals are in dealing with this system? Does air leak past the damper seal? Is a rope seal at the rear going to let air past as well?

I know Rover went to a composite lifter valley pan which is really quite good. Was this because of air leaks?

Are there other places where a 20" vacuum in the crankcase can pull air into the system?

You guys are the best around on technical issues, I'm wondering what your thoughts are about this.

Jim


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1165 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

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Re: British PCV: How good is it?
Posted by: ex-tyke
Date: July 26, 2014 01:53PM

Quote:
... an orifice to allow metered and filtered air into the crankcase.

Is it naive of me to ask if orifice size can dictate the amount of vacuum/pressure seen in the crankcase?. Is it possible to size the orifice to get close to neutral or slightly negative vacuum?....then engine sealing becomes less relevant.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 26, 2014 04:30PM

I don't think so Graham. The typical orifice will be less than .030" and not much air will get in that way, certainly not enough to offset a 1/2" or larger tube to the manifold. Plus it would make the idle completely uncontrollable. But not a bad thought.

Jim


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

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Re: British PCV: How good is it?
Posted by: Moderator
Date: July 26, 2014 06:25PM

Quote:
I know Rover went to a composite lifter valley pan which is really quite good. Was this because of air leaks?

Sealing may have been a factor, but I expect noise reduction was probably enough reason for Rover.


MG four six eight
Bill Jacobson
Wa state
(324 posts)

Registered:
10/23/2007 02:15AM

Main British Car:
73 MGB Buick 215, Eaton/GM supercharger

Re: British PCV: How good is it?
Posted by: MG four six eight
Date: July 28, 2014 08:45PM

Jim,

Depending on the seal used you may see a small amount of vacuum pulled down past the dist/cam sensor drive. In this case though, my main concern would be the vacuum constantly sucking the oil away from the upper bushing. Or at least in theory.

Bill


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

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Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 28, 2014 10:36PM

The British or European style PCV system doesn't put the crankcase into a vacuum situation.
The metered orifice is the only piece of the system that sees manifold vacuum.
And as the bleed is stable it doesn't affect the idle speed.
The bleed is used to keep a constant airflow through the crank case.
And draw off any small amounts of blowby that may have occurred under light load.
The larger hose is used to route gross amounts of blowby to the air intake system.
Generally just before the throttlebody, but sometimes into the intake hose or air filter.
Not the other way around as most people think.
I tried putting full manifold vacuum on a small block Chevy once.
It caved in the valve covers and timing cover. And sucked in the valve cover gaskets and manifold end seals.
But not before it destroyed both crank seals.
I think my Dad let me off easy as it was his work truck.

Cheers
Fred


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 29, 2014 11:41AM

Interesting Fred, I hope I haven't been giving bad advice on these things. I think we need to see some venting diagrams of some Rover vehicles. I know that's a very large area to be applying a vacuum to, and the pan could be a problem area. The front lip seal could let air by but I don't think it would deform. Doubt it'd hurt a rope seal either. Never even thought about the lifter valley tin on the Rover. (not a problem on the 300 or 340) That would be subject to some pretty high forces. 15 psi x width x length. A quick estimate gives about 3/4 ton, yep that would be a problem. So I'm wondering where I came up with this idea? It worked on my 215, maybe I have ventured into an alternate reality?... That would explain some of the little glitches I've been seeing lately...
Take careful note guys, this doesn't happen that often.

Anybody got a diagram handy?

OK then, in practical terms it sounds like on *my* car I need a quick acting vacuum valve on my vent line. (because it is under full vacuum and cannot easily be ingested otherwise due to the Enderlie blower scoop design. Something with a 5/8 or 3/4" bore that closes when vacuum is applied. Maybe some sort of EGT valve or something.

Jim



ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1165 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

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Re: British PCV: How good is it?
Posted by: ex-tyke
Date: July 29, 2014 03:59PM

Jim, diesels use a crankcase depression regulator in the ventilation system - similar to PCV but larger in size - maybe there's an opportunity to use one.
Here's one example:
[www.ssdieselsupply.com]
...and some basic operational specs...
[www.flashoffroad.com]



Edited 1 time(s). Last edit at 07/29/2014 04:22PM by ex-tyke.


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

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Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 29, 2014 06:40PM

Jim,
What if you just put an inline PCV valve in the vacuum line and opened the restricted line up to the air cleaner?
You would then have the American style system with a European holiday thrown in.

Cheers
Fred


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 30, 2014 10:09AM

Graham, thanks for the suggestion, I'll look into that. I was also considering a vacuum controlled heater valve: [www.ebay.com]
which is closed by vacuum. How much vacuum I don't know.
Fred, the air cleaner is inside the Enderlie scoop, which is at manifold pressure except during boost, as the throttle body is at the scoop inlet. There is no place to plumb the vent line. The alternative would be an open vent or a road tube, neither of which is a very good option.

The other thing is, at idle there should be some draw through the valve, but it should be a controlled amount.

Jim


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 30, 2014 12:27PM

Most, if not all PCV's meter air at high vacuum levels. Bigger engines meter more and visa-versa. So choosing one from a similar sized engine should get you there. The vent line could simply go to a small K+N that is made for the purpose. Or they also make valve cover mounted ones as well. Whatever the case the vent needs to be filtered as it would be drawing air most of the time.

Cheers
Fred


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 30, 2014 02:41PM

I'd rather not just leave an open vent line, even filtered as it will spew oil vapor on WOT which will settle all around and make everything oily.

I just looked at photos of the Rover and it seems pretty clear that the large vent line from the flame trap goes to a bung on the throttle body which is upstream of the throttle shaft. The opposite valve cover has a filtered orifice.
[c7716.r16.cf2.rackcdn.com]

So, assuming this is the intended configuration at least for that year (3.9L), it would seem that the system is almost entirely passive. The only pressure drop applied would be from the inlet air going through the main air filter and through the airflow meter. Clearly any airflow through the orifice would be minimal.

At WOT of course blowby would be directly routed to the throttle body and a small amount would escape through the orifice.

But it does not appear there is any vacuum applied to the system anywhere.

Jim


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 30, 2014 09:54PM

That vented orifice on the left valve cover is intended as a vacuum break. It's meant to prevent oil being trapped in that valve cover.
The system isn't really passive per se. The vacuum connection is off the T on the vent line. It runs through a restriction into the lower 1/2 of the plenum.
Your situation is a little unique. You can't run a PCV under the blower because it will see boost and pressurize the crankcase.
And you can't vent at the air filter because it is under vacuum.
So I would still suggest a filtered vent of some sort and running a positive crankcase ventilation valve up to the air filter. Even at WOT there will be some negative pressure there. And if the flow is insufficient enough to cause blowback through the vent then run two PCV's
Or run the PCV line through a venturi at the air filter. That would provide a linear pressure drop directly related to engine load.
I have a couple more ideas if those don't tickle your fancy, but I've got a scotchy scotch waiting so I've gotta go.

Cheers
Fred


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 30, 2014 11:24PM

Fred, I see the "T" you refer to, are you saying this goes to vacuum through an orifice? About the only way that really makes sense is if there was something to close off the line to the throttle body so it could pull vapors from the crankcase. Obviously there is still quite a bit about this system I am still are not familiar with. I don't quite buy the vacuum break explanation for the filtered orifice. There are no shortages of windage passages into the rocker box and I can't see them being blocked with engine oil. I do see it as an inlet for filtered air for PCV flowthrough, but to make that work some level of vacuum has to be applied. That can't really happen if it is escaping through the throttle body. I would really like to understand what's going on here.

I picked up that 4 seasons heater valve #74857 at AutoZone for about 9 bucks. It is a plunger type valve and has a positive seal. Plumbed it into the large vent line between the scoop and the Rover flame trap pulling the vacuum on the upper side of the valve towards the diaphragm so that the vacuum would pull it closed instead of open. Plumbed the diaphragm into a manifold vacuum port. It stays closed at idle but will open at WOT. That shuts off the high vacuum signal to the crankcase but should vent the blowby under hard acceleration. Looks pretty tidy too. The only real question is at what level of vacuum does it begin to open?

I considered the CDR but Diesels have no throttle plates and therefore do not develop the vacuum of gasoline engines so I went this route.

That leaves the drawthrough aspect to consider, and that could be accomplished with a metered orifice from the manifold to the valve cover. Something to think about. As this arrangement has allowed my idle to come down to a very reasonable 600-800 rpm (before tuning), I can afford to bleed some air and have some leeway in orifice size. The restriction in the small inlet filter on the opposite valve cover can be removed (enlarged to the 1/4" NPT nipple ID). I think that will work, and will allow some blowby to escape if the valve does not open early enough. I'll need to fit a hose barb to the left valve cover that has the flame trap. I'll try to get a photo tomorrow.

But back to the OEM Rover system. I had missed the "T" in the vent line. Is it possible that something in the valve body blocks off the vent line when the throttle closes? One of the primary claims of the PCV system from the very start was that it pulled fresh air through the engine and kept combustion byproducts from accumulating inside. In order to do that isn't something needed a bit more than a gentle suggestion that the air move along? So far that's really all I'm seeing.

Jim


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 31, 2014 03:30AM

Here is a picture of the T piece Jim.
w01331630345apa.jpg
The brass insert is the orifice and it connects directly to the manifold plenum.
No magic occurs at the throttle body, just a straight through passage in front of the butterfly.
A slight pressure drop is maintained by the natural resistance provided by the air filter and its plumbing. As well as the inlet airhorn on the filter housing. The Air horn serves two purposes, one is to muffle intake noise. The second and more important is to provide a pressure differential for the breather system.
The Vacuum break on the left valve cover only existed for a few years and was deleted when valve stem seals were introduced.
My understanding is that oil was building up in the valve cover and causing high hydrocarbon emissions.
This is highlighted by the fact that on teardown the left cylinder intake valves are always carbon fouled and the right is usually clean.
The use of the vacuum heater valve is very clever but I'm worried about it's ability to tolerate oil, fuel and combustion gasses. And where does the blowby go when the valve is closed?
What you have created really is a complex version of the lowly PCV valve. Under high vacuum it's closed (and meters a small amount of air). Under low vacuum/high flow situations it's wide open. So why not use a normal PCV valve?
And to everyone watching this is not an argument, it's an exchange of ideas between what I consider friends. (I received a couple of comments)

Cheers
Fred



MGBV8
Carl Floyd
Kingsport, TN
(4511 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

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Re: British PCV: How good is it?
Posted by: MGBV8
Date: July 31, 2014 11:25AM

Just sounds like friendly brainstorming to me.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 31, 2014 11:33AM

Right, no argument going on here in case anybody is wondering, Fred and I are the best of friends and I value his expertise.
So a gentle suggestion that the crankcase gasses move on along it is, eh? Then perhaps this is what distinguishes it from the American approach.

OK. The reason for not simply sticking a PCV valve in the large vent line is because I am not aware of a PCV valve which is that large. (5/8" to 3/4"). It needs to be that large because as we have seen in other examples (Carl for instance) smaller than that can lead to massive oil consumption as the engine wears and blowby increases. Also, the traditional PCV valve closes down under two conditions. The easily understood high vacuum of idle, but also at high flow rates under excessive blowby. Which is not a problem with a large vent line to the air cleaner bypassing it, but if you raise the spring rate of the valve to keep it open during blowby you also keep it open under higher vacuum and that mode of operation is probably not compatible with my system. The part of the heater valve of questionable durability is the sealing o-ring. And possibly the diaphragm. Is it viton? Is it buna-n? Nobody knows. But if it fails it is a common part, inexpensive, and easily replaced. It could in fact be regularly changed at oil changes if needed. You know, change the oil, change the PCV valve.
Here is an image:

IMG_0007.JPG

The vent on the other valve cover is the original tube with orifice. Turns out I simply slipped a sleeve of tubing over it and pushed on a small filter element. I will be thinking seriously about perhaps enlarging that to a 1/4" NPT pipe stub.

That "T" gives me some Idea of the size orifice which might be suitable in the valve bypass line. One advantage of discrete circuits is the ability to selectively vary each piece. One disadvantage is more tubes and lines running around. Perhaps I should just weld or braze a bung into the Rover flame trap.

Jim



Edited 1 time(s). Last edit at 07/31/2014 11:35AM by BlownMGB-V8.


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: British PCV: How good is it?
Posted by: DiDueColpi
Date: July 31, 2014 01:06PM

Another though just struck me! I tried to duck but it still hit me square in the head.
You could run the vent line, or all of the crankcase gasses for that matter. Through a checkvalve into the low pressure area of your header collector. The collector always has a negative pressure differential and the check valves (common ones) are available all the way up to 3/4" Almost every AIR system made uses a version of these valves so they are cheap and easily found.
Something like this.
images.jpg
Or even one of the electronic ones. (could be run by your megasquirt.)
Cheers
Fred


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: British PCV: How good is it?
Posted by: Moderator
Date: July 31, 2014 05:21PM

"checkvalve into the low pressure area of your header collector"
AlternativeCrankcaseVentilation.jpg
(Coincidentally, I took this snapshot just last weekend.)

"Or even one of the electronic ones. (could be run by your megasquirt.)" That's an interesting idea. I suppose you'd plumb some sort of MAP sensor to the crankcase to facilitate optimizing valve timing? Wouldn't it need to register both positive and negative values? Can you get sufficient data from existing sensors?


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: British PCV: How good is it?
Posted by: BlownMGB-V8
Date: July 31, 2014 08:37PM

I heard that those collector vacuum things don't work so well at part throttle and with mufflers,etc. Hey, just what I heard so I'm only passing it along. I don't know anyone with real life experience with them.

Guess I could plumb it into the bung for my EGT... only when MS3 goes in I sort of planned on dual O2 sensors.

Jim
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