Dry Sump Breathing? 2

[Spimage]

I am running a Cobra Replica with a Chevy V8 377 cu.in., with a dry sump, 3 stage pump, ( 2 scavenge, 1 pressure ).
A breather on the one valve cover and a PCV valve on the other, going to the throttle body. From the resevoir tank ( capacity - 8 liter ) I have a 1/2" flexible pipe to a breather tank which is mounted where the distributer normally sits on a Chevy intake manifold. ( Haltech Management system, crank trigger ignition etc.) This tank dumps any oil which would come from the resevoir, back into the crankcase. The breather tank has a regular valve cover type breather / filter at the top.
Have I made provision for sufficient breathing for this motor which revs to 7500? Your valued comments on this will be appreciated.

Warren

 

[patprimmer]

The scavenge pumps should more than remove blow by from the engine unless you have a ring seal problem.

Seal up the engine and add breathers to the dry sump tank.

If you are pulling to much vacuum in the crankcase, install a small or preferably a pressure regulated breather. If you pull a significant vacuum, you will need special oil seals at the crank and to take extra care with the tappet cover and sump gaskets

Regards

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[patprimmer]

If you don't wish to pull a vacuum, you could run normal breathers to the top of the dry sump tank.

With the current system, how do you intend to regulate which breather is for in and which is for out, as they will both see the same positive and negative pressures at the same time.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Spimage]

Thank you Patprimmer for your prompt response and expert advice.

The motor is still pretty new and I'm not particually looking for vacuum or positive pressure in the crankcase, if I am wrong here, please forgive me for my ignorance.

My objective is to prevent what has been happening, ie; oil surge in the dry sump tank, causing oil to enter the breather pipe to the breather tank which in turn was spewing oil onto the exhaust header, hence my reason for wanting to dump the oil from the breather tank back to the crankcase. That being said, I am busy relocating the breather pipe on the DST to a 75mm dia.x 75mm high (header tank?) which I am welding onto the DST, which I believe will prevent the surge problem in such.

Your valued comments on the above will be greatly appreciated.

Regards.

 

[patprimmer]

It really boils down to observation and common sense. keep the oil level well clear of the breather.

Give the area under the breather enough room for any oil carried with the fumes room to separate out and return to the DST.

Within reason the narrower and higher the DST tank the better.

The scavenge line should strike the side of the tank at a tangent so as to avoid splashing and air entrapment.

It is wise to have a horizontal baffle with a slight fall toward the centre and a substantial hole in the centre. it should be just above the normal running oil level. This will contain oil surge by preventing it from climbing the wall of the tank.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[sprintcar]

If it's a 3 stage (2 scav, 1 Pres) you may want to keep a breather on the motor in addition to the sump tank.

I was running the sealed engine/vented tank with a 3 stage pump and had oil leaks. Checking with Barnes (who made the pump) and the engine builder, they all recommended 4 stage pumps for sealed engines. I'm sure leakdown/blowby etc. will affect each motor differently, but once I added the rocker cover breather back, the problem vanished. When I had the Moroso 4 stage on a sealed engine, there were no problems.

Just food for thought.

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