m73m95

Restricting oil flow of #1 & 4 main bearings .....

https://rennlist.com/forums/924-931-...l-galleys.html

Chris White

Its another Band-Aid fix (it might be a good one – but still a Band-Aid).

The real problem is many different elements –
1) Aerated oil – the crank will aerate the oil like a blender way to easily, especially in the 2.5 engines. Most folks don’t think about the movement of air in the block – as piston 1 comes down the full volume of air has to travel past the girdle (under the crank) and back up into the 2nd piston cylinder. That’s a lot of air moving around at 100 times per second (6k rpm). In addition when you brake hard (1G braking at the track is common) half the oil in the sump ends up in the front of the pan with the crank whipping it up.

2) Thin oil – hot oil is thin oil. 951s have hot oil….some have very hot oil!

3) Oil pump – known to cavitate at higher RPMs – made worse by thin aerated oil.

4) Crank oil passages – the stock crank has right angle turns in the oil passages – again, made worse by thin aerated oil.

5) Oil distribution – some folks have studied this and I believe if you fix 1, 2 and 3 it is not a problem. (same goes for 4 – if the first 3 are fixed then you can overcome 4 with enough pressure. can addressing jsut this help? Possibly but I would rather fix the root causes than the symptoms. The one plus of this fix is that it is fairly cheap if the engine is apart.

Chris Prack

I had some new crankshafts lined up a year or so ago. New design, lighter, proper oil passages etc. But when push came to shove, the person selling them opted for idiotic barrel valve carbon fiber intake manifolds that were more than twice as expensive and a disaster to complete. Not to mention the possibility of stepping on someone else's toes.

badcoupe

I drilled my crank on the outermost part of the rod journal so the oil had to come out regaurdless of rpm. Perpendicular drilling it's called. This was a problem onn some of the old GMmotors and drilling themthis way was a good fix. Not saying what I do will fix the problem but I certainly haven't had any failures doing this.

m73m95

So Chris, how do you solve these problems?

Thick oil .... 15w-50... thats easy.

Do you recommend cross drilling the crank and if so, were (all 4 or just 2 & 3)?
Any way to improve the stock oil pump?
Should we all be using a windage tray and/or crank scraper?

I know restricting the oil flow to 1 & 4 is an "easy" solution, but if the end result is even flow to all 4 journals, why is it a "bad" solution?

V2Rocket

drilling, good cooling, and scraper.

JohnKoaWood

Dry Sump... no oil sitting in the pan to be aerated, slosh to the front on hard braking, feed can be directed to where it is needed, you can use any sort of oil cooling needed based on your actual observed loads, and gets rid of the problematic designed oil pump... of course it comes with it's own set of issues...

fixes all the problems in one fail swoop... and is WAY beyond what most folks on here are thinking about doing to their street motor and time soon...

Techno Duck

You know ive been thinking about dry sump. Figure the cost of a spun bearing and potentially needing a new crank, maybe $1k max in parts, machine work..not to mention the inconvenience of potentially being stranded where ever you happen to be, down time from having to drop the engine if your crank is toast and your time (or paying for someone elses) to replace everything.

Cost of dry sump, figure about $4500 when you factor in all the lines and fittings also? Worth the cost of admission to fix one of the Achilles heals of these cars? Not to mention possibly freeing up some power.. .

I wish it was possible to quantify what a pan baffle, good oil cooler, windage tray and modified crank did for the reliability of the bottom end.

333pg333

Why limit it to 15w/50? We use 25w/60 for the track with the view that all oil will get hot and thinner.

Chris White

To me the only ‘solution’ is a dry sump system – and that ain’t cheap! The other stuff that is out there is not a solution to the problem but they do address some of the individual symptoms.

Don’t get me wrong – I didn’t say that the oil restrictor was ‘bad’ – just that it did not fix the root cause of the problem. There are only two common fixes that I think are bad – accusump and over filling. Both can cause more aeration – which is a really nasty problem.

The dry sump system really start to make sense when you have a lot of dollars tied up in the parts. Blowing a rod out of the side of a 2.5 turbo is a bummer, blowing a rod out of a 3.1 16v race motor....more than a bummer!

JohnKoaWood

That is, by my estimate, about 250% of what most folks could squeze out for a full rebuild... hence the lack of 3L motors round here... hence my desire to build a 3L motor... and now I Spy with my little eye a 16V head that needs a valve job... mmmm... 3L 16V dry sump, big turbo.... WOO HOO

Chris Prack

I have an S2 motor complete if you are that interested!

V2Rocket

that could become problematic on a cold day in a street car, but i guess if you stick to the track on nice days it will be fine