Dry sump tank breathing

[Risking]

I have a dry sump RB26 and im having tank breathing issues.

Its using a peterson 11 litre tank
Barnes 5 stage pump. 3 pick ups from a custom sump and one pick up from the rear of the head.
The rocker cover breathers are blocked off but the dip stick has been removed to allow some minor crank case ventilation.
The main tank breathes from the top into the bottom of a 2.5 litre tank via a -12 hose, the tank then vents from the top via another -12 hose out to the bottom of the boot.
The main tank is only 2/3rds full when the engine is warm and running at idle there is minimal breathing from the lines.
The engine is also new and never had any breathing issues prior.
The breather tank is mounted slightly higher than the top of the main tank however the line between the two does go down hill then back up into the bottom of the breather tank.
The main tank has all the baffles and so forth that the sprint car team used to use it with.

The problem I have is that after a few hard laps at oran park over the weekend the tank had breathed oil out all over the boot.
So the next session we put the breather line into a bottle and went back out. It breathed about 1/2 a litre into the bottle over 10 laps.
Same thing the next session. We never filled the main tank back up as I thought at first that it may have been over full. It kept breathing oil into the 2nd bottle every time.

Im now not sure if my breathing system is correct and asking for advise regarding how people normally do this.

Many thanks in advance.

Brad....

[RB30-POWER]

correct me if i am wrong, but i would have thought a breather or catch can system would still be needed, regardless of the oiling system.

your going to have big crankcase pressure with big horsepower, no matter how good your rings are.

how much power, 500-600 or more?

i'm interested in this as well.

[10sec rx7]

you will still need breathers off the rocker covers, these usually vent to the oil tank when the tank is in the engine bay, then into a catch can..

i would just unblock your rocker cover breathers and put them into a decient sized catch can.

we also ran sump breathers on big power RB's but all were wet sump

[RB30-POWER]

that setup you describe dale sounds and looks almost like what the gibson gtr has on it.

[Risking]

there is no real need for breathers with a dry sump system such as this so I am told.
I have vacum in the crank case so why would the rocker covers and crank case need to breath?? There is no positive pressure to vent.
If I uncover the breather holes ill loose my negative crank case pressure.
Its not the engine thats breathing heavily its the oil tank in the boot thats breathing/spilling out oil. Its breaths into a catch can/tank but that seems to fill up....

Its roughly an 800hp engine.

[RB30-POWER]

dunno if this is of any help.

http://www.eng-tips.com/viewthread.cfm?qid=125180&page=1

[PLAYA]

well i know that some people have to have a "vent" in the engine because the pump is sucking too much air and creates too much vacuum, so what you have done with the dip stick is fine, as long its got the correct vacuum.

Also why don't you run a say 3-4L catch can next to the dry sump tank, have a few baffles in it to catch the oil and have a return at the bottom of the catch can to the main tank? Not sure if its done like this but would work. Ony think i can think is that the -12 breather is too small for the amount of air the dry sump is pushing, as you corner and the oil is sloshing around it can blow it out the breather on the main tank.

edit 1: also i just read that you vent into the BOTTOM of the catch can, this would mean that any oil that does collect will be pushed up and bubbled by more air being pushed into the catch can, move the main tank vent to the middle of the catch can.

Edit2: also am i blind but how is it leaking oil into the boot when the catch can is vented out the boot by a dash 12 line?

[Glenno]

Have you checked the vacuum level with the dipstick blocked and unblocked?

Where you having issues with it sucking the sump in or was it a just in case measure?

[10sec rx7]

there is no real need for breathers with a dry sump system such as this so I am told.
I have vacum in the crank case so why would the rocker covers and crank case need to breath?? There is no positive pressure to vent.
If I uncover the breather holes ill loose my negative crank case pressure.
Its not the engine thats breathing heavily its the oil tank in the boot thats breathing/spilling out oil. Its breaths into a catch can/tank but that seems to fill up....

Its roughly an 800hp engine.

every dry sump setup i have ever had anything to do with has had breathers on the rocker cover... but they were only 120hp forumla fords...

id like to see a vacuum/boost guage on the crank case at full boost at 8000rpm and see what the pressure is doing..

[Glenno]

Rule of thumb is around 7 psi below atmospehric pressure. Moroso (i think) make an adjstable vacuum reg for the purpose with a sintered brass filter.

[gmh265]

You should be running your engine with about 18 inches of vac, no breathers on the engine. best way to vary the vac level is to change the drive ratio of the pump and use the oil relief valve/change size of pressure stage to get the oil pressure right.

Any air that gets vented into the engine (in this case through your dipstick bleed) comes out the breather in the boot, therefore increasing your engines apparent blow-by and taking your oil with it. I would be suprised if you have any more than a few inches of crankcase vac with a dipstick sized bleed.

the breather from the oil tank should be large as possible without being stupid (-16 is nice on a v8) and should go from the top of the oil tank to the top of the catch tank, with the catch tank being baffled between its inlet and outlet. also try and run the line between the two tanks up and then down in an upside down 'U'.

has the system you are running ever worked or is it new?

[Billzilla]

Needs pics of it please.
As mentioned above you need breathers in the cam covers, but not to the catch tank - if the dry sump system is working properly then the air will flow into the top of the engine, not out of the top. To keep the correct vacuum inside the engine you should run either a restrictor in that line or some kind of vacuum regulator. As mentioned above, you need about half atmospheric pressure inside the engine. You do not need a crankcase breather.

[Risking]

The system was in another GTR I owned prior to this one but it only ever did one meeting and had the same issues.

I have 12inches of vac at 9700Rpm at 24psi boost. We had a gauge on the rocker cover during the dyno tune.
On the previous car we had the breathers going into the top of the catch tank but it filled up so we thought this time we'd try and breath from the bottom so any oil would run back to the tank.

here are a few photos of the current system

http://i2.photobucket.com/albums/y3/strawberrysil/Tankbottom.jpg

http://i2.photobucket.com/albums/y3/strawberrysil/Drysumptank.jpg

http://i2.photobucket.com/albums/y3/strawberrysil/Breather.jpg

If I were to breath the main tank in near the top of the catch tank and have baffling between the feed and the breather obviously. Then run the bottom fitting to the bottom of the main tank would this allow the oil to return to the main tank and allow the tank to breath sufficently??

I have also now blocked off the dip stick and ordered a regulating valve to fit into the rocker cover.

[Supashake]

All my customer cars run sealed engines with the breathers on the oil tank only,Theres good power running vacuum on your crank case.Some pumps are to small for this tho and still need engine breathers

[Billzilla]

The system was in another GTR I owned prior to this one but it only ever did one meeting and had the same issues.

I have 12inches of vac at 9700Rpm at 24psi boost. We had a gauge on the rocker cover during the dyno tune

<snip>


I have also now blocked off the dip stick and ordered a regulating valve to fit into the rocker cover.

Sounds like you're pulling enough vacuum, you just need to get the airflow going the right way and that seems to be under control now as well.
Top to bottom is the way the air needs to go.

[Risking]

I think the whole air flow thing is more than likely my problem.

I have the tank out atm changing a few fittings around so ill take it back out this sunday and see what happens

[Steve]

How much oil do you use on an average oil change?

[Risking]

a totally dry engine thats been rebuilt and all the lines flushed out will take about 10-12 litres from memory.

[Risking]

short update on this for future referance

Fully sealed engine NO rocker cover breathers and a vacum valve on the rocker cover

I cut the tank in two and fitted a baffle plate with a few holes. The fitted a -12 fitting 3/4 the way up the tank but below the baffle plate. Then welded it back together

I ran the top of the main oil tank to the new -12 fitting 3/4 high. The top fitting I vented to the outside of the car and the bottom fitting I ran back to the main oil tank right on the oil level. Probably just above it.

After a day at Eastern creek it had absolutly no breathing issues what so ever. I ran the vent into a plastic bottle so if it did breath I wouldnt ruin the circuit. There was not one drop of oil in the platic bottle after the day was done.

Thanks for everyones advise, one less thing to worry about come race day.

[Billzilla]

Yay, we helped. :D