Negative crankcase pressure with a dry sump

[Virgil]

Help - is this normal?

I have a Duratec installed in my escort running the SBD supplied Titan dry sump pump. I have read that these should be run with a sealed engine so have capped all the engine breathers. The tank is mounted in the engine bay and is vented to atmosphere. When I run the engine (even at idle) the crankcase vacuum is high enough that it is difficult to lift off the oil filler cap, and when I shut the engine down I can hear air being sucked back in for about 20 to 30 seconds afterwards.

[Jim_S]

When I installed a dry sump (Pace system) on my Cosworth YBT engine in my RS200 replica I had a small return line from the top of the dry sump tank (swirl pot part) which had a small non return valve fitted. The idea behind this was to allow the negative pressure to suck any oily fumes back to the engine and also break the vacuum slightly.

This also then meant that the oil catch tank which I had fitted from the dry sump tank didn't get any oily fumes if everything was working correctly.

But I have seen other systems with no return line but the top of the engine has a very small hole 1-2mm) in a cam cover take off pipe to allow the vacuum to break.

I have also seen them like yours and each engine builder has said theirs is the correct way.

All I can say mine worked very well and it ran 460+ BHP


Jim

[Jim_S]

When I installed a dry sump (Pace system) on my Cosworth YBT engine in my RS200 replica I had a small return line from the top of the dry sump tank (swirl pot part) which had a small non return valve fitted. The idea behind this was to allow the negative pressure to suck any oily fumes back to the engine and also break the vacuum slightly.

This also then meant that the oil catch tank which I had fitted from the dry sump tank didn't get any oily fumes if everything was working correctly.

But I have seen other systems with no return line but the top of the engine has a very small hole 1-2mm) in a cam cover take off pipe to allow the vacuum to break.

I have also seen them like yours and each engine builder has said theirs is the correct way.

All I can say mine worked very well and it ran 460+ BHP


Jim

[stevieturbo]

Some will some wont, just depends on the actual pump and setup used.

But if it is pulling vacuum, which is no bad thing it would be wise to fit a check valve somewhere on the breathers to actually limit how much vacuum can be pulled.

[Virgil]

From my google research it seems that a vacuum is really good, but I also agree I need to fit some sort of relief/check valve to limit.

Thanks for your responses.

[MK1_Oz]

Is crankcase vacuum another of these horsepower old wives tales? Alot do it but I have never found a back to back test on a dyno done. Just pondering....

[Lacey]

You want neg" pressure
It helps the engine , you only have to much when the seals are
Being sucked in which causes a squeaky noise

Neg" pressure can variey due to a number of thing
Pump effiencey
Engine seals strength
Piston and ring clearance

Na will normally pull neg pressure through the revs
Where a turbo engine will get blow by at revs due to boost

My friend builds engines for the burgcup and other events
And he has done a lot of testing with engines with dry sumps
Ref" negative pressure
And has always says there much better with more
This is why he uses may kits as he can pull more neg pressure

If a one way valve is fitted
It needs to dump at about 5/10 psi

And on a na it needs to let the engine breathe in
And on a turbo the valve needs to let the engine breathe out

Hope this helps

[MK1_Oz]

Unless the sum of the scavenge side of the pump has a much greater capacity than the pressure side then even a dry sump will have a quantity of oil in the bottom. If there is a certain depth of oil then the scavenge side of the pump will only ever pull oil and never air from that sump i.e. never create a vacuum. My weaver 3 stage pump has 66% more scavenge capability (2 x 1.2" vs 1 x 1.45" gears) although I am not sure by how much the long return line via a filter and cooler reduces this capability (I did have a damaged scavenge section which would have reduced capability significantly). I should therefore have an empty sump at all times and be creating a vacuum but there is no way of knowing.....Now that I have a Picoscope I will be measuring real world block pressures!! ........mythbusting time........??

[Sultzi]

Peterson fluids makes a nice adjustable vacuum regulator with filter for drysump systems
http://www.petersonfluidsys.com/engi...Regulator.html

[Lacey]

Probably no good for turbo application
As once it comes on boost the engine goes from negative
To positive pressure

[stevieturbo]

Probably no good for turbo application
As once it comes on boost the engine goes from negative
To positive pressure

The above in no way connects to anything that boost would affect it. And it is a suitable valve to use for limiting vacuum in the crankcase on a dry sump system where it will pull vacuum in there.
n/a, boosted, whatever.

[Lacey]

I've been involved in dry sumping
Engines for 20 years
I machined pumps/kits for the super touring cars in 1999 and onwards
And for a lot of the big names in the industry
All these people done test after test
N/a and turbo
With the info being fed back to us
So I think you will find I do know that boost will
Effect negative crank pressure

Boost will alway find its way here there and everywhere

The only reason you want a one way valve on a n/a dry sump engine
Is because The pump ( if you have a good one ) will pull the seals cause
A squeak noise and the possibility of pulling dirt in

This is the same on a turbo engine till the boost cuts in
Then blow by will happen
hence the one way valve is turned around to
Breathe out so once the blow by get to high it can bleed
It off
or it can blow the seals out

This has been proven time and time again

[stevieturbo]

Please explain how "boost" will find its way into the crankcase ?

And the valve listed above is a vacuum limiting valve to prevent excess vacuum being created in the crankcase. Used all over the world without issue.

And nobody has asked for a one way valve ?

[Graham]

Please explain how "boost" will find its way into the crankcase ?

ring blowby, you will always get some under boost

[stevieturbo]

And equally combustion of all sorts can generate cylinder pressure which if you've a crap ring seal can lead to some blowby.

So there is little difference n/a or boost, and that is not "boost" finding its way into the crankcase.

[Graham]

agree, but you dont get 100% seal with any ring, and combustion pressures are much higher than N/a so you will get more blowby

[Lacey]

Lol
Oh dear
All my findings are based on facts from the top end of race team/company's down to the
Humble engine build testing on dyno

New rings will blow by to
The only ring that reduces it to a minimum are total seal ring and there still not a 100% seal in turbo engines once max boost is reached

Lol now your excepting there is a little difference between na and turbo as you say above
If it ain't boost what is it then as the only real main difference is the lung bolted on the side of the engine


To be honest mate I am getting bored of justifying fact to you sorry
So believe what you want to believe mate it make no difference to me

[stevieturbo]

Of course it is not boost, it's combustion pressure. The two are not the same.

And the valve listed does the job it is listed for and is correct for a dry sump that pulls vac in the crankcase regardless of the application.

[Graham]

Of course it is not boost, it's combustion pressure. The two are not the same.

.

your splitting hairs, whether its boost or combustion pressure matters not, when the engine is under high boost you get more blowby and the system isn't going to hold a negative pressure

[stevieturbo]

It isnt splitting hairs, it's being factual.

If the system cannot pull vac in the crankcase, then that is inadequacies with the scavenge pump system in use. Not any filter valves used, or boost, or rings, or anything like that.
The pump is either capable or it is not...design it right from the outset.

And if cannot pull vac, then design a breather system to suit !

[Graham]

It isnt splitting hairs, it's being factual.

If the system cannot pull vac in the crankcase, then that is inadequacies with the scavenge pump system in use. Not any filter valves used, or boost, or rings, or anything like that.
The pump is either capable or it is not...design it right from the outset.

And if cannot pull vac, then design a breather system to suit !

`i think the problem here is with a high boost engine, if you could still pull a vacuum under full load/boost then off boost the vacuum would be so massive you would suck the oil seals in

[stevieturbo]

Which is exactly why you use the Peterson valve listed above ! It will limit the amount of vac you can pull to prevent that happening and is adjustable so you can decide how much vacuum you allow it.

[Lacey]

Lol

This is funny now

First you went on about the valve
Then say I was wrong about the rings and everything else

Now your stating the obvious about the pump being up to the job

Just out of curiosity would you argue that black is white

No need for a answer I think I know already
But maybe that's wrong to lol

[stevieturbo]

And who is arguing black is white ?

You claimed boost made its way into the crankcase, that is factually incorrect.

You were the one saying that valve/ref/filter is of no use on a boosted car...which again is factually incorrect.

You make claims as if all n/a engines have absolutely zero blowby from combustion/cylinder pressure and that is unique to a boosted engine...again 100% incorrect.
You claim a boosted engine with dry sump will never pull vac...which again, is 100% incorrect.

Or did I misread what you have said ?