bebbetufs

There is a huge overlap in the oil returns between the girdle and the block. Has anyone enlarged these to improve drainage of the head? Would you consider it safe to remove material in this area?

Pic one shows the overlap on the girdle and pic two shows the overlap on the block, the corresponding hole in the girdle is outlined in red.



What are your thoughts on this overlap?

bebbetufs

No one? Perhaps this has been discussed before, but I've searched and searched and come up with nothing.

fortysixandtwo

I don't think the flow of oil is great enough for the profile change to cause a return issue.

bebbetufs

You may be right, but if the oil is frothy it can back up the drain. This happens a lot with turbos. An example is the return from the turbo, it is huge yet the flow is much less than from the top. Blending the two openings is not a lot of work so I will do it if there is no risk of loosing the alignment of the crank bearings or weakening the block.

Tom M'Guinn

I'd be worried about weakening the girdle or block, but it is curious they don't match up...

Van

Isn't that just a gravity drain from the head??

ZR8ED

I have done port matching, on just about every mating surface. Both oil and water passages. Anything that hinders flow in an engine, is not desireable. Granted results are very minor, but every little bit helps. If you have the time and ability,then go for it!

kev951

overkill......

bebbetufs

Interesting points of view in here.
The reason I'm even looking at this is because of the allegation that some #2 rod bearing failures could be caused by the oil gathering in the cam area and not being able to drain back fast enough increasing the risk of the pick up becoming uncovered and sucking air. Supposedly this happens more at the ends of straights when the long period of high revs really gets the oil pump going. At the end of a straight the hard breaking sends the oil to the front of the pain further increasing the risk. I don't know if this has been verified as a cause of rod bearing failures, but if porting these holes could possibly increase flow back into the sump and lower the risk then I don't see why it's not a common modification, which judging from this thread it is not. Perhaps the area simply is too weak for porting to be safe, the placements of the drains on the side of the bearing bridge could indicate this.

Anyone else but ZR8ED who has done this?

ZR8ED

I don't think this is a popularly done mod. I don't think most people even think about this stuff, though when you are working with small displacement engines, getting the most that you can may only offer limited gains, but gains nonetheless. Or maybe this stuff is top secret for folks who are spec racing (insert name of vehicle or class of vehicle) where the racing is so tight, a couple of hp maybe all that you need to get ahead. (rules permitting of course)

I tried every trick I could dig up years gone by when I was on a quest for 100hp/litre in N/A form (non Porsche) Only three basic ways to get there. VE, compression, and rpm.

GregBBRD

Looking carefully at this, you'd have to think that Porsche must have done some of this mis-matching on purpose.

This is not off by just a little bit....it's like two different people on two different continents made the drawing for the block and the cradle....without ever talking to each other.

ZR8ED

You will have to look at it and make your own decision as to "how much" to port match. You don't always have to or are able to completely port match mating surfaces, so there is nothing wrong with helping to "transition" the mating surfaces. to promote less turbulant flow.

As for how helpful it may be, think of how chamfering the oil passage/exit in the crank can drastically promote oil flow to a bearing. Seems pretty minor, but has drastic effects. (I'm not saying this about this particular port match question)

seafeye

Looks like to me that it would be there to build pressure. It's so far off that I wouldn't mess with it.

bebbetufs

Thanks for chiming in. I'm intrigued as to why they would want to build pressure in the head. To lubricate the lifter faces?

GregBBRD

They don't want to build pressure. They want the pressure to be reduced, so the oil can more freely return to the crankcase. On the 4 valve engine, the head can/does "hold" over 2 quarts of oil, at higher RPMs.

Those sharp angles are going to actually be an "edge" that oil can "catch" on and be "restricted" from going up into the head. Think of them as "tiny" oil separators.

If you really want to improve the oil return from the head, look farther up in the block, and "massage" that area.