dr bob

Hmmm. While the spring is important, the shape of the port and the amount of oil that will flow through the engine at a given pressure may be the bigger issue. A coil spring is hardly a constant-pressure device-- it's pounds of force to displacement that's predicatble. How much oil flows through at a specific spring displacement varies widely among different engines; Bearing clearances and oil viscosity probably determins a lot of that. So, looking at a 20+ year old spring and saying that it was wrong when the engine was built? Um... At the same time, it's not real practical to spec a universal spring for those same 20+ year old engines. At this point every used engine will probably need to be individually tweaked with different springs and shims.

I want to remind myself here that the reason we want such high oil pressures is to compress the air bubbles in the foam, right?


Trying to follow along at home...

marton

Joe posted
OK with points 2 -7 but myself I am still not convinced about drilling the crank, simply because Porsche themselves did not do this.

Trying some alternative crank drillings and testing in the factory does not sound like a big deal for Porsche; they must have tried it & found reasons not to go that route.

On the other hand I could imagine some Porsche Engineers sitting at a table with an accountant & deciding that developing a totally new scraper, windage tray or similar was just too expensive with no guarantee of success so they did not go this route.

Marton

GregBBRD

I built a windage tray set-up and a pan spacer, because I needed something to help with these issues in my own engines. I don't offer them for sale. I don't have the time to build extras for anyone else! I guess I might live in a cave, but was totally unaware that Kevin Johnson even existed or that he built windage trays and scrapers. I don't read every thread and really don't have much free time to research threads. When he began making comments on this tread, I was initially interested in the exchange of ideas. I'm sorry he took this the wrong way and became....annoyed at me and became a bit defensive.

I went to his web site, a few days ago, and looked at what he has built and offers. Looks like great stuff! The 928 scraper seems like a very nice piece. I will probably buy a system from him and give it a try. I'll certainly combine it with my pan spacer....can't hurt to move the pan away.

My concern here was not that Kevin was promoting his product, I could care less. If you have something great to offer....you should be able to say so! My concern was that he was essentially saying that his system was a "cure all" to the oiling problems in the 928 engine. I do not agree with this, but that is my right to do so. I think there are other things that need to be done to make the oiling system work better. I offered up the 944 GTR as an example of the crank oiling problems, because of the drilling problem, but this was ignored.

No big deal to me. I'll continue to build engines my way. Drilling the crank a "more modern" way is certainly not going to hurt the oiling problem. I'm certainly not going to call Moldex and have my custom cranks changed to the "Porsche" style of center oiling!! Whitey would not build me any more cranks!

Kevin: I hope you put your 928 windage tray system back up on your site...I have not looked, but I assume your word is good and that you have indeed removed it. It looks like a great system...way better than my "wimpy windage only" attempt. To suggest that you might not want to build another system....that's not what anyone here wants....especially me! I'm very interested in your thoughts and products. The "cold" accumsump idea at Road America is testimony enough for me....that tells me something significant is happening!! Either the switch is screwed up and the thing is not working....which I'm sure is not the case....or great things are happening!!

Please accept my appology. I was not attacking you....I just don't agree that a windage tray is going to solve all the issues with the oiling problems. You have your ideas and I have mine....no big deal. Like I said, I would like to try your system....and will. I also have a big block Chevy I'm putting together for my Chevelle....you got something for that?

Another point that needs to be made....not to Kevin, as I'm sure he knows this. The 2/6 oil galley to the crank is indeed the closest one to the oil pump....that makes it the last one to get oil! Fluid dynamics are different that one would expect on initial inspection. Fluid always travels to the end point and them "back fills" the void (in this case, the oil galley). This is relatively easy to see and prove to one's self. Go buy a "soaker" hose from Home Depot. Hook it up and spread it out. Turn on the water. The water runs to the very end and water comes out of the holes at that end. It gradually back fills and the last holes to spray water are at the end closest to the water source. This is about as close an example of what happens in an engine as possible.

Vilhuer

Brand new out from bag genuine Porsche later style spring, not used 25 years old original. Timeline what happened once again in much clealer format.

1. '81 ROW 4.5L engine needs rebuild
2. Its taken apart to last nut and bolt, block split in pieces etc
3. Original relief valve spring doesn't look too good so its not going back no matter what
4. Engine is put back together with new main and rod bearings (this doesn't make any difference anyway as old ones would allow this same oil pump rotating measurement done anyway, might take little longer to build up pressure but it would go to same relief valve value anyway)
5. Brank new latest part number original genuine Porsche relief valve spring is installed exactly like PET shows meaning without any washers and pressure measured by rotating oil pump while belt is off
6. Release pressure is found to be 5.5bar
7. Several mm's worth of washers are added and pressure is barely going up, stock part is deemed insufficient
8. Glyco is contacted to see what they have to say about design parameters for main bearings, no real reply
9. Some generic spring (meant for who knows what, spring is a spring) which has correct dimensions is installed
10. Several different thickness washers are tried until little over 8bar is reached with 1mm thick setup

Very simple really. New correctly installed Porsche spring didn't give expected result. Now the question is who is willing to bet 10 out of 10 Porsche springs are all going to give 8.5bars? Since measurement is easy to do I don't see whats big deal in here. This is just one more thing to check and adjust if needed. I will not trust stock part enough anymore to use it without checking. Others seem to trust it blindly as its Porsche part. In conversation regarding oiling problems in stock parts this sounds very strange to me.

Bill Ball

Most of the time I eventually find I don't know what I'm talking about. Who really KNOWS? So, leave that out of discussion and just say why you disagree rather than blowing up the discussion with accusations. This applies to both sides here.

jon928se

Tongue firmly in cheek. You must be a slow learner Bill. I learnt a long time ago the most of the time I don't know what I am talking about.

Back on topic, sort of some idle observations/questions-

Aerated or not aerated oil (or any liquid of the same density) requires the same static pressure to overcome the centrifugal force in the crank holding it back.

The oil gallerys in the block don't sit at a constant "static " pressure due to the flow of the oil under pressure they are affected by hydrodynamic losses and will have varying pressures due to these losses.

Aerated oil will experience different possibly dramatically different hydrodynamic losses due to it's compressibility. (Oil with no air entrained is close enough to a "perfect fluid" in hydraulics terms - ie incompressible.) This will lead to a whole different pressure regime in the oil gallerys

Does the oil pump suffer cavitation pumping aerated oil ?

SwayBar

Wow, good stuff!

Do you have any idea where this generic spring came from?

Also, is the engine running yet, and does it have an aftermarket analog oil pressure gauge, and if so, what are the engine's various oil pressures?

Ian928

Another point to that may or may not be worth considering is the ejector effect. I once was trying to create an even "waterfall" for cooling aluminium casting without cracking the casting by using a perforated tube with inlets on both ends. Everybody expected most water to come out of the holes closest to the inlet, but this was not the case, in fact water passing over first holes had such high speed it created so much suction it counteracted the pressure inside the tube and air was sucked in instead. The solution for us was to reduce the outlet holes, creating a bigger pressure differnce to counteract the ejector effect. The 5-8 bars in our oil system is probably enough to counteract the ejector effect, but what do the experts say about this theory?

If the ejector effect is contributing to our problems, maybe this is part of the German "drill a hole" fix.

Vilhuer

Not excatly but I bet its from some industry supply cataloque as he has access to some which are not available to general public. There is also one specialist spring shop in here which can source lot of different types or make custom springs if needed.

Not yet as gearbox and suspension work is in progress.

Block lower half has sort of opposite setup than GTS manual gearbox oil feed pipe. Block channels get shallower further away from oil pump while gearbox pipe has larger holes further away from feed. I think this ways will result much more even distribution than one depth channel in block or same size holes in gearbox.

GregBBRD

?????????????????????????????????

Same thing. Pressure is created by a restriction. The first major restriction is the oil pressure relief valve. One this is open, the oil channel begins to fill and get pressure...at a much lower number than seen before the oil pressure relief valve. Since it is a system that leaks at many places., it is exactly like a soaker hose. The whole uncompressability of a fluid and what happens to that fluid changes when there are leaks in the system.

BTW. I know what you studied. I was a Chem E major. We studied a bit of this.....

Go buy a hose and check it out! Full or not, the end farthest away starts spraying out of the holes first.

Jim bailey - 928 International

So with the old very brown 1980 on Kuhmos at the Streets of Willow when I see the oil pressure gauge drop down and bounce around after a hard turn what is happening ? based on the above comments am I about to be "hosed" . After a 15 minute session pressure at idle trips the warning light , oil is redline racing. It has been doing this for 4-5 years

Jim bailey - 928 International

Why do I only see the needle drop in corners ?

atb

Too busy wavin' at the fans in the straights?

LT Texan

My condolences. My roommate was a Chem E. He had no social life in college and was jealous of my free time (Business major)

John Veninger

Now why are you looking at the oil pressure in a corner