blocking off breathers from head (k) what with?

[Peter Carmichael]

As a variation on the metaphor...

 

... take your glass of drink and straw. Now seal them. Now try and suck the drink out...

 

Stoopid.

[Tony C]

Maybe there's too much noise at anything other than idle.

 

Logic dictates that data logging would give reliable "Look inside the engine while it's operating" data and the sealed glass and drink straw analogy makes sense, but I can't believe that the clucking sound is air being drawn through a seal somewhere - maybe the noise is from the scavenge pump trying to slurp-up oil which isn't there - air and oil - slurp.

[Rob Walker]

Peter,

 

I agree in a properly designed dry sump system the scavenge should have redundent capacity to remove all oil that is pumped into the engine throughout the operating range of the engine. The CC/titan system for the K is compromised in that the two pumps are not linked by a common shaft and both pumps are of differing capacity and operating characteristics. At low revs when the engine is hot ( piston ring gas seal is at its best and crankcase pressurisation is at a minamum) the scavange pump has the overcapacity to suck out all the oil and create a partial vacuum, oil & air are sucked out intermittently at this point the funky Chicken can be heard.

 

I have never heard the funky chicken on either a sealed K or Duratec that runs the fully external three stage pump system driven by a common shaft and having twin scavenge pickup points, presumably the engine breathes more effectively through one of the pick ups when the other is pumping oil

 

Rob

 

 

[Tony C]

Mine has the three stage external Pace pump. An occasional cluck can be heard at idle.

 

I can't imagine the crankcase pressure would be too far off ambient. There would be some piston blow-by, which would tend to increase crankcase pressure, but I can't imagine the scavenge pumps can reduce the air pressure - they are only capable of sucking out more oil than is being delivered. The scavenge return pressurises the oil tank, from which both breather lines pressurise the catch tank and back to atmosphere.

 

There must be a circulation and therefore logically pressure differentials to achieve that.

[Jason Plato]

why not try fitting a pressure guage on the cam cover and see whats happening ?

 

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[Peter Carmichael]

This post is a bit of a thought process, prompted by the statements so far. At the end I think i might have explained the source of the cluck.

 

they are only capable of sucking out more oil than is being delivered.

 

They are positive displacement pumps. They pump volume. They don't care what that volume is made up of. The equilibrium pressure is achieved as a mathematical relationship between the relative volumes of the scavenge and pressure pumps (taking into account pressure relief) and the quantity of blowby gas (and other sources of gas whether leaks past seals or anything else). The oil is incompressible. The gasses are compressible.

 

Remove one of your seals and put your thumb over the hole. A simpler version of Dave's pressure gauge.

 

There would be some piston blow-by, which would tend to increase crankcase pressure

 

Yes. I'll just add the word "equilibrium" before "pressure".

 

The dry sump scavenge is designed to remove all the blowby volume and then some. You might be talking about a tendency for the equilibrium pressure to settle a bit higher with more blowby, but it is not significant unless the engine is already badgered.

 

There must be a circulation and therefore logically pressure differentials to achieve that.

 

Not sure what you're saying. You have used the word "pressurised" relating to the tank and catch tank. These are small differential pressures. The only big pressure difference is across the pump. Pressure, incompressible fluids and volumetric pumps are a strange combination. A volumetric pump transporting an incompressible fluid will produce pressure depending on what that fluid then passes through - in this case: large bore pipework and a fairly open breather to atmosphere. There will be pressure pulses indeed, but largely no acceleration of the flow. In the case of a scavenge pump where part of the volume is incompressible and part is compressible and scavenged at lower than atmospheric pressure, the compressible portion will reduce in volume when transported to the tank side of the pump.

 

Perhaps this is the source of the cluck. It sucks back down the pipe from the tank.

[Jason Plato]

Thats a long way of saying you dont know 😬

[robmar]

ok - I sort of wished I never asked 😬

 

anyway just so you know after a quick discussion with DVA who has built the engine I am going to seal the breathers at the crankcase and head (and plenum) , and we will see how we go

 

rob

[Rob Walker]

Peter may be right air could be sucked back down the scavenge line back from the tank,

Rob,

I had thought of this possibility and run with a small foam filter on the end of the vent to air coming out of the bulk oil storage tank which I have discharging below the car.

 

I also run with a small micro switch set up against the auto belt tensioner on the scavenge pump, in the event of the belt going AWOL " Peter knows all about this" it puts a large yellow warning lamp on on my dash. This is one advantage of the CC external pump system in that you should have cira 20 seconds to shut down the engine before all the oil is transfered from the bulk tank into the engine.

 

With the Pace fully external system its instant loss of pressure.

 

Rob

 

 

 

 

 

Edited by - Rob Walker on 31 Jan 2006 10:27:02

[robmar]

Rob

 

small foam filter on the end of the vent to air coming out of the bulk oil storage tank

---

 

am assuming you mean from the top of the bell tank hosuing (in the standard CC system case), Mine runs up to a catch tank on the bulk head, so I would be putting the foam (what type 🤔 where from 🤔) into the end next to the catch tank. DVA also mentioned putting in some sort of foam/filter into the catch tank am asusming this would get the same result 🤔

 

dry sump failure warning system, that nice man V7 made me up an aluminium plate and micro switch to do the same thing before he sold his caterham, already have the warning light plumbed in , which is a nice cluster of incredibly bright diodes with 2 colours, red is for low oil pressure and green will be for belt gone AWOL 😬

 

rob

[Rob Walker]

Rob.

 

Its been my experience that if you simply let the catch tank vent to air under the bonnet especially mounted on the scuttle bulkhead that at slow speeds you can smell the oil vapour discharge as the tank vents. Therefore I have a 18mm ID pipe running from the top of my catch tank discharging below the passenger floorpan, on the end off this pipe I have a foam filter.

 

Rob

[Rob Walker]

Rob,

 

To answer your original question which has got lost in this thread, I block off my cam cover vents with a plug of High temp Silicon Sealant, make sure you degrease the vents so it will stick. CC sell neat rubber plugs for the specific purpose.

 

Rob

[robmar]

Rob - ta

 

my catch tank vents via a pipe down under the gearbox area, which does result sometimes in a small pool of oil

[Peter Carmichael]

Peter may be right air could be sucked back down the scavenge line back from the tank

 

Just to clarify. The cluck is, I believe, a momentary suck back as each pump chamber opens into the discharge area containing a partial vacuum. I would not expect a net flow back into the system and I cannot see there being a need for a filter on the end of the catch tank vent.

[david nelson]

I have just had a look at Dave J engine pic (see his post here.

 

Dave looks as if the breather goes streight back to the cam cover.

 

David

 

SL #146

 

Edited by - David Nelson on 8 Feb 2006 18:56:03

[scottydog]

With the Honda engine we have installed, it runs in a totally sealed state, the rocker box is vented into the dry sump tank via flapper valve, so if in a positive pressure at tickover it can vent out, but when running at revs, the engine runs in a vacuum state.

 

On the dyno we found that running it this way increases power by around 7bhp

 

I`m unsure of why he has done it this way, but the figures seem to prove he knows what he is doing.

 

Just to add, my VHPD had its cam cover vents sealed up, by a small peice ot tube with a bung in the end.

 

Scotty

[robmar]

David N - are you sure

[Peter Carmichael]

Go to be careful of what you mean by a "breather" and when it is just a "hose".

 

Dave's setup appears to have a single hose linking the top of the dry sump tank to the cam cover. A second hose disappears from the other connection point on the cam cover. It would appear that the second hose is the breather, exiting via a catch tank.

 

This achieves very much the same effect as the non-sealed options I described earlier. There is a circulation of gases via the dry sump tank and then the net volume of the blowby gases is vented via the catch tank. Job done.

 

Also, this will make use of the normal circulation paths in the engine, encouraging oil drainage from the head.

 

Edited by - Peter Carmichael on 9 Feb 2006 12:33:25

[Jason Plato]

*thumbup*yes thats correct

 

and the catch tank breather has a pipe exiting under the chassis with a small filter on it

 

I'm not keen on the vacum crankcase method. I like to equalise the pressures on either side of the engine/oil system.

 

Dave

 

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[david nelson]

Some questions as still unclear.

 

The hose from the top of the remote tank goes into the cam cover.

 

then another hose comes of the cam cover to the red catch tank.

 

? Reading an earlier i thought both breathers sucked, so how does the catch tank work?

 

In a nut shell i have a D/S with the remote tank. is this the right way to set it up.

 

from the top of the tank 1 hose to the catch tank and a 2nd hose to the breather on the cam cover.?

 

do i also need to have anther hose going from the catch tank to the atmospher?

 

thanks

 

 

David

 

SL #146

[Mathew Rimmer]

David,

 

Are you not describing Peter Cs option A from the first page in your right way to set it up paragraph ? I am thinking of going this way.

 

I have currently blocked the second tank breather and have the cam breather breathing in the airbox. I am wondering if a simple connection between the 2 will reduce the amount of air venting by the catch tank (which seems to be quite a lot currently)

 

Why does there have to be so many options and no "right" answer, this is waaay to complicated !

 

 

[Peter Carmichael]

The two breathers on the cam cover of a K are not linked to the same internal passages. One of them is linked to oil drainage passages from the head to the crankcase. This is the one that Dave has linked from the top of the dry sump tank.

 

The other is connected to the passages that return gas flow from the crankcase. This is the one that Dave has linked to the catch tank.

 

This setup maintains a circulatory flow assisting oil drainage and is the most consistent setup I have yet seen for the dry sumped K.

 

In this setup, the two breathers do not both "suck" because the gases are being forcibly fed back into the engine. They are being pumped back in by the dry sump pump. The net volume ejected via the catch tank is the sum total of the blowby gases.

 

Clever. Copy what Dave's done... but don't get it wrong.

[Jason Plato]

dont forget the filter on the end of the catch tank outlet as air is sucked into the system at idle.

 

if you want more details feel free to call me this evening

 

Dave

 

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[Peter Carmichael]

I'm not convinced that air is sucked into the system at idle. I suppose it could.

 

Total volume of the DJ system is: internal cavities of the engine + volume of the dry sump tank. All of this volume is now linked via open hoses, so the volume only marginally varies from atmospheric pressure.

 

This volume is full of air and oil. The oil just gets moved from the engine to the dry sump tank and back again. If there is any momentary accumulation of oil in the engine it displaces air that moves to the tank.

 

The only net change in the system is blowby. This additional volume of gas needs to be expelled and forms the net outflow of volume from the breather leading to the catch tank. The possibility for breathing in through the breather can only come from "blowby" operating in reverse, which I suppose could happen with a partial vacuum formed in the cylinders on the overrun, but less likely at idle.

 

I've just noticed that the DJ setup will not necessarily result in the system ejecting excess oil into the catch tank. You will instead get a lot of oil being recirculated via the hose back to the cylinder head. This is not necessarily a good thing. Any comment, Dave?

[Peter Carmichael]

Of course Dave's engine would be making 254bhp if he ran it sealed. My 🙆🏻.