Dry Sump Tank Question

[GTRNUR]

Hi everyone,

Ive got an engine with a 4 stage dry sump pump and I have a question about oil tank venting.

The engine is fully sealed. From what I understand the 3 scavenge stages (which are 1.75" stages) should be able to pull the crankcase into a vacuum around the -10 to -15 inHG. Of course all this air that is sucked out of the block plus cylinder blow by ends up in the main oil tank and must be vented. I'll be doing this by a remote mounted vent with a couple of filters on it which is the pretty much standard approach.

My question is, can I put a one way pressure relief valve in line between the remote vent and the filters in order to lightly pressurise the tank?

My thoughts behind this is if the tank is lightly pressurised (to about 1 psi) this will assist oil flow to the pressure stage. With 1psi pushing oil to the pressure stage and a low vacuum on the other side of the engines bearings. The reason I want to do this is the length of the hose between the pressure stage and the tank is quite long because the oil tank is in the boot. The hose size I am using is -12. The pump pressure stage is 1.25".

I'd appreciate any thoughts other people with dry sump experience might have about this.

Cheers,

Ian

[The Dan]

Yes, the boot should be able to hold the oil you are going to blow out of the tank.

But seriously, creating the vacuum in the engine means pressurising the res. tank. If you don't vent it properly, you will not only restrict flow into the tank from the pump but also cause the oil to try to escape the tank. I don't think there are any secrets left in dry sumps so just do what everyone else does.

[r33_racer]

If your tank is in the boot...I believe you need atleast -16 lines to and from the tank to pump. Anything smaller and it makes it hard for the pump to suck it over that distance.

From memory the peterson guide says -12 for upto 3-4 foot anything greater then its -16.

Ive never heard of anyone doing what you are suggesting....but you can always be the first to try and find out the results first hand.

Edited December 16, 2009 by r33_racer

[GTRNUR]

Thanks for the info. Im able to run a -16 supply line without too much trouble.

I have a ERL501 thermostat and a pair of oil coolers running on the return line before it returns to the tank. Is there any rule saying that a -12 return line isnt large enough? I figured because its returning to the tank and not under pressure it should be fine right?

[r33_racer]

Im not 100% sure...We ran -16 on both lines. Something to do with the large amount of air/oil being pushed and pulled through the lines. I think so long as the pump supply line is -16 you will be safe as thats the critical one.

Make sure you do it with a single line too if possible, eliminate the use of multiple lines and fittings, as they can cause problems.

[bigmikespec]

Generally in hydraulics we (at work) always have a larger hose and fittings on the return as a good practice measure.

[T04GTR]

you could cheat and use a 1" alloy pipe to run most the way and have a nice bulkhead fitting in the firewall with your hose to the pump. etc.

[GTRNUR]

Afraid not, there just isnt a way to get the plumbing through the car now... I should have run pipes through the chassis before the car was 95% assembled. Now all thats left to do with it is wire the ecu and run the oil supply and returns. This is another one of those things i'll put on my list of things to do should I ever scratch build a race car again.

Edited December 18, 2009 by GTRNUR

[dazmo]

I run a -16 return line and a -12 feed to the oil pump with a 3gallon tank in the boot and have no issues with oil pressure. A -12 will be fine for the pressure feed. What sort of pump do you have I run a peterson pump and it has -12 inlet on the pressure side and all the scavage lines and a -16 fitting for the return line and is supplied by peterson in that configuration.

I personally would not try to put any sort of pressure relief valve in the breather line from the tank as you do not want it pressure in the tank at all best bet is just to breath your oil tank into a catch can and then vent this can thru the boot floor so you dont fill the cabbin with fumes/

[GTRNUR]

I should have posted all the details from the start... so here goes.

The tank is mounted at about the same height as the pump, so there is no down hill flow for the oil. Im sure that only helps for priming the pump but has little effect on the pump operation when the engine is running.

The pump is an RPM 4 stage pump. 2 x scavenge stages are 1.75" and use -12 scavenge lines, and the 3rd scavenge stage uses a -10 line. The pressure stage is 1.25" and is all -10 from the pressure side to the engine. From the pump it blows through a remote filter and straight into the engine.

I just spent the evening finishing off the -10 plumbing for the oil coolers to the thermostat. The thermostat return is a -10 hard line.

The return line from the pump to the thermostat is yet to be purchased, but it will be easiest to setup with -12 as that was the fittings that came with the pump.

The supply line has to go through the firewall and has 2 x 90 degree fittings (one off the tank and the other at the firewall), 1 x straight and 1 x 130 degree fitting at the pump end that is a size adapter from -16 hose to -12 fitting at the pump. Based on what everyone is saying I should be keeping the supply a -16, not only because of the length involved but also because of the bends and fittings that will be in the line. I estimate the supply line will be about 4.5 Meters and the return line will be about 5 meters.

I was planning on using a -12 vent line to the catch can. Venting through the floor makes good sense too, thanks for that.