Oil Pressure for racing engine

[Gertvr]

I have done some research on oil pressure and found mostly 10psi/1K rpm to be the guideline. (pls correct me if i am wrong)

This held true for my production engine and pressure got capped off just above 60psi ( at least that is what the gauge indicated) which i assume is being controlled by the pressure regulator in the block even if the RPMs went to 7K.

What i have not found in the research (maybe i just missed it) is what is required for a race engine that spins up to 8K, is the same 10psi/1k rpm ratio applicable?

If so how do i get to 80psi, by shimming the spring ?

Thanks

Gert

[lucittm]

You can increase the oil pressure by using a heavier weight oil. If you are running 15W40, try 20W50 at your next oil change and see what that does.

There are two oil pressure regulators in our engines. One (spring length 89mm) is vertical and is designed to lift at a nominal 90 psi (6.2 bar) and pass oil directly to the crankcase. The second one (spring length 70mm) is horizontal and is a safety valve that lifts at a nominal 116 psi (8 bar) to prevent damage to the oil cooler, oil filter, and oil lines; at least in my 964 turbo.

Mark

[lindemans]

Key is you want higher pressure and as a result more oil flow.
Adjusting the pump and /or the regulator springs is the way to do that.

Other measures, like thicker oil, increase pressure through reducing the flow. That is not the way to go !!! You can easily increase pressure too by narrowing oil channels, it will increase oil pressure but kill oil flow....

[lucittm]

lindemans,
Could you explain how to adjust the pump? I am not aware of any procedure except rebuilding or replacing the oil pump.

I believe viscosity of motor oil varies with the temperature of the oil. If the oil is too thin at normal operating temperature, the pressure will be too low. For example, fresh 15W40 will act like 40 weight oil at 100 deg. C (212 deg. F). And it follows that fresh 20W50 will act like 50 weight oil at the same temperature. 40 weight oil viscosity is 12.5 - 16.3 cSt (centi-Stokes) while 50 weight oil viscosity is 16.3 - 21.9 cSt. So we are starting out with a thicker oil at the higher temperatures. If Gert needs 20 cSt to get to 80psi at 212 deg., he needs to run 20W50.

Gert did not say what oil he is currently using or what temperature his oil is but an increased viscosity of 3.8 - 5.6 cSt, going from 15W40 to 20W50, would cause some resistance to flow but the difference in High Temperature/High Shear rating of both oils is near 3.7 cP (centi-Poise) anyway, so the resistance to flow for the heavier weight oil is minor, especially considering the lack of oil compressibility and the positive displacement oil pumps that Porsche uses.

Mark

[Gertvr]

Thanks for all the responses. I am already running 20W50 and it gets pretty hot in Atllanta but the oil temp remains between 180 and 200F. My main question was if the continuation of the oil pressure ramp of 10psi/1kRpm above 60psi, where mine got capped, is this required to cover the higher RPMs for a racing engine. To put some numbers around it, would I need 80psi , or higher @ 8Krpm.

For the 2nd part how do i get there if it is needed, i agree with Lindemans reducing the flow further is not a option. Are there different spring rates available or do i have to increase the pressure by shimming the spring seat of the regulator.

Ps. I will be installing a GT3 pump in the SC case so both flow and pressure potential from the pump should be adequate.

On a side note what is the safe maximum oil pressure.

Thanks
Gert

[TimT]

Ps. I will be installing a GT3 pump in the SC case so both flow and pressure potential from the pump should be adequate.

When you do that, worry about another issues. That is a great oil pump..then let your relief and bypass springs control the pressure...

With you set up you wont have to worry about oil pressure

[lindemans]

Originally Posted by lucittm

lindemans,
Could you explain how to adjust the pump? I am not aware of any procedure except rebuilding or replacing the oil pump.

I meant replacing the pump for another one here...a bit of work :-)

[JohnJL]

Hi Gert,

The GT3 oil pump into the SC case requires some mods but they are not too difficult. Remember to order in an new, shorter pumpshaft.

Here's how I did it...GT3 Oil Pump Into 3.0SC Case

[Gertvr]

Thanks guys,

Great Write-up John. I am not that adventurous and will send it out to be done. I want to get a line hone on the mains anyway and will combine the 2.

Gert