Chris White

Very true – but its also just about impossible to fit a dry sump system on to a street car and keep all the stock systems functioning!

Chris White

That depends on a lot of variables. If you are using a light flywheel you don’t want to take too much weight off the crank – you will have stalling problems with a grippy clutch. Turning a crank is not the easiest job – you need to make sure you are removing the same amount of weight for each journal to keep the torsional damping at its best.

The way the oil pump is driven makes it pretty much impossible to upgrade it. The only possibility is to use a belt driven external oil pump. That is possible but you will have to give up either power steering or A/C. You will also have to give up a large sum of cash do get that done right!

KSira

Chris, won't a good oil cooling solution solve most of the problems for us who doesn't have the $$ to go dry sump? Having seen how bad the stock oil cooler works in cold Norwegian condition, it's no wonder that rod bearings are broken in the temperature you have. I run a massive 60rows oil cooler and still get 110deg C on a "hot" (for Norway) track day. With stock oil cooler it would probably be in the 140-150 range.

67King

110 isn't really that high if you are running a good oil. For example, Millers CFS oils are good for 125 continuous, 150 peak. That is 250 and 300 in F for fellow Yankees.

KSira

110 is acceptable. 125 is way to much in may opinion, even with good oil. If you have 125deg on the oil going in to the engine, imagine how hot it will be once inside the engine.

67King

Temperatures are usually taken in the sump, which is before it runs through the oil cooler, and after it has been "worked" through the bearings, bores, etc. So we may not be talking apples to apples. But in the sump, 125 (255F) is very common. 135 (275F) is starting to get considered hot, and 150 (300F) is a shut down temperature (and that's usually due to other problems, not with the oil!). Note the oil doesn't flash until 200 (390). This is not specific to 944's, moreso the oil. 115 (240F) is about the lowest I've seen in sump temps on track cars (with gauges I know worked). I do know of one car that indicates lower, but it indicates oil temps below coolant temps with the stock oil cooler, so I don't trust the readings.

Besides, once you are at operating temperature, oil viscosity is pretty stable as you get hotter.

bebbetufs

KSira How wide is your cooler and where is it mounted? I'm about to buy a cooler and I want to be sure it's not too small.
Also, where do you measure the temperature?

bebbetufs

Chris don't you think that the absence of the windage holes you describe here can be a major reason for the bearing failures? I want to have such ports machined in the block. Even drilling a few holes should help. If I remove the pistons from the block there is no way I can keep the old rings is there?

M758

I have studied the engineering behind this and based on the equations I believe that oil flow not pressure is key. Pressure is not critical, but flow rate of oil into the bearing is important. If the flow rate is low or the oil volume is replaced by air bubbles you have problems. I believe that a second hole improves oil flow because the as system oil flow through crank to the 2 & 3 journals is in fact limited by exit hole. These are acting as the metering orifice. Now I have not done the fluid analysis of the oil system to validate this, but if correct it would show a respone similar to what Greg's testing results were. Given limited testing and analysis tools at my disposal I have decided to go with it. It could be wrong, but since I have no magic bullet I believe everything you can do to help is good. My solution is to run alot different things. Incuding in that is oil of the highest quality and heavy weight. I change it often make sure its full and not over full and use a turbo oil cooler in my 944 NA to lower oil temps.

M758

No direct data to support this. Bearings sping at just about any time. If it were a simple signal point of failure it would have been resolved. The fact that the best "soltions" are band-aids or "Dry sump" tells me the issue goes very deep in the motor design.

KSira

I still think cold oil is a cheap way of ensuring that the engine components does not have to high operating temperature. In my view, as much heat as possible should be removed from the engine and its compartment. So far a blown head gasket that looked like it was the original one from 86 is the only failure (knock on wood)

EDIT: Above 120 deg in the oil pan is no go for me

EDIT2: Just out of curiosity, are there any test available that shows how the oils lubrication ability is effected by increased heat?

KSira

It's measured in the oil pan, at the oil drain plug, which is the coldest part with air constantly flowing over it. The cooler itself is mounted about where the stock IC would go.

67King

As a matter of fact, these kinds of tests are run pretty regularly. This one is of a very well known player in racing oils. Note how poor the film thickness is until the oil gets sufficiently hot. Also notice the coefficient of friction gets lower with more heat.




Also, here is an interesting article. I looked the guy up, as when a "Dr." began talking about owning multiple Ferraris and Lambos, I questioned what kind of Dr. that was. MD, not Ph.D. But the guy has done more research here than probably anyone on this thread other than Chris White. Note he addresses some points about flow versus pressure, etc. http://www.minimania.com/web/display...8/ArticleV.cfm I assume when he specifies a "thickness," the actual number is centistrokes (cSt). Note a 10W60's viscosity at 100C is about 22cSt, and a 5W40 is 14 cSt.

KSira

Than you, that is quite interesting. It does not say anything about the oil film strength. Do you know if this is proportional with oil film thickens or are other parameters playing a part?

67King

The green line is an electrical measurement taken across the two surfaces. 100% means it is completely insulating (and a 100% thick film), and 0% means there is complete electrical conductance across the two surfaces. This is a lab test, which has its own set of caveats, and not all oils have the same characteristics. But I put it up there to show that racing oils are designed to run at elevated temperatures. The higher numbers are better.

Sorry I didn't catch that before I posted it. I've looked at it enough that I forget it needs interpretation.