?aux 911 oil tank

aircooledsonly · 12-16-2005, 04:13 PM

This is a question for all you rocket surgons out there. I'm still in the fab/design stages of building a 1972 RS clone light weight [2150 lbs.], 2.7 ltr. mfi, solex cams, 9.2 comp.,SC suspension,wilwood 4 piston calipers f+r [they weigh 2.7 lbs. , stock iron =16 lbs. Designed to stop a 3300lb. Camero should be adequate], old school chrome trim and period correct 7" and 8" BBS wheels, and painted bamboo 'lawn furniture' green.QUESTION IS: Given that the 72 oil tank is only 8.5 qts. could I fab an aux oil tank of 5 to 6 qts to fit in the smugglers box and plumbed into the return line of my front RS oil cooler. Would I gain anything with the increased oil capacity. WHY? I had a problem with oil arreation in my old car [2.8 ltr C-6 RS bodied 70 911 @ 1910 lbs], solution to problem then was a Dick Troutman fabed 18 qt RSR tank in smugglers box., but this is a 'street' car.I have fabed a card board mockup with dearreation screens in design,provisions for fill and drain and sight glass on top. This will all be plumbed in -12an. Aux tank will be lower than stock tank so backdrain won't be a problem. I'm open for any thoughts, suggestions, questions, ideas Thanks Jay

TRE Cup · TRE Cup's Garage

no need jay
cut that tank about a 1/3 of the way up and splice in a section, thereby expanding the capacity by at least 3 quarts. don't forget to extend the tubing inside

Grady Clay · 12-16-2005, 04:59 PM

Jay,

Good question. The simple answer is you can have only one oil sump tank for the pressure pump to pick up oil.

The ’72 design was a good one except for the oil capacity. The flow of oil was in the right direction. The problem for Porsche was the flow of money was in the wrong direction with that expensive set-up.

One of the customer complaints at the time was they could hear the oil gurgling in the tank when cold. They hocked their gold chains and bought a gelding.

So, how should you do it? I would build as large tank as possible within those confines. I understand it is possible to increase the capacity by two or possibly three quarts. If you are willing to move the inner panel inboard, you can get significantly more.

Another possibility is to have an “overflow tank” as high as possible in the engine compartment connected to the oil tank by the breather hose. This allows you to run the oil tank all the way full when cold. If the oil gets too high, it just goes up into the overflow tank. When the circumstances change (higher revs, cooler oil) the oil simply drains back into the oil tank. Note this is very different from a “catch tank” that doesn’t drain back. The crankcase breather should connect high to the overflow tank and a breather to the world come out of the topmost of the tank with baffles. The breather should go to a large (4-8 quart) catch tank that is easy to drain as you experiment with how much oil you can use without having it go into the catch tank. I have done this successfully on several track cars.

I’m assuming you are going to use a front cooler and have the oil filter console with the thermostat and pressure relief valve.

Best,
Grady

Tyson Schmidt · 12-16-2005, 05:57 PM

He double-posted, and I responded to the other thread. I wonder if the moderator could combine the two?

aircooledsonly · 12-16-2005, 06:07 PM

sorry about double post , I don't know how to undo it , help please as to how to remove post

aircooledsonly · 12-16-2005, 06:15 PM

"Evil" isn't oil cooler in reality an aux oil tank, think about it ? If you had a 5 qt oil cooler what would call it ?

Tyson Schmidt · 12-16-2005, 08:19 PM

The oil in the cooler isn't available to the suction side of the oil pump yet.

It has to be pumped back to the top of the oil tank, and then get de-aerated by the screens, then settle in the bottom of the oil tank before it is available to the pressure pump.

Up until that point, it's just more work for the scavenge pump.

The key issue is to have a large "reserve" of oil ready and waiting for the pressure pump on it's supply side. Oil in the oil cooler or an "auxiliarey oil tank" is still a long way away from being available to the pressure pump.

The larger oil tank means that there is more likelihood of still having some oil left in the tank under high rpm, high G-force conditions.