namasgt

do you have to make the notch on the bearing too or the notch is not deep enough to affect the bearing?
what is this process called, I have a friend that builds hot rod VW engines, type ones and type IVs, he might know somthing about this.

Lizard928

You do not enter the bearing area AT ALL.

mine will be a semi circle in this same area

dr bob

I don't have a feel for how much this 'relief' would actually direct oil splash towards the piston. Or how much oil is needed to make a difference in piston temps. Would the actual heat carried from the piston be worth the additional oil mist? Would there really be any added mist, or would it be the net same as without the groove since that oil needs to escape anyway?

As far as the weakening, the small hole you show in the picture wouldn't worry me that much on a stock engine. Concern would mount as pressures, temperatures and RPM's did the same. No data to back up my concern, just that the factory had a specific operating condition in mind when rods were originally spec'd. Pressure and RPM's in your turbo car will exceed those original requirements. Now add a possible fracture site on purpose. Again, no data to support or debunk this idea. I say go for it, and report your results. FWIW, you should see temp changes in the oil that might be used to help determine the efficacy of the cooling mist.

Lizard928

If it was not enough to pull heat out of the piston then many manufactures and aftermarket people would not be doing it.

Porsche themselves have even done it. For example the 924 with a flat head and piston (terrible combustion chamber shape), they used this technique to keep the piston temps under control.

ptuomov

Ok, here's the notched rod. Oil, meet piston.

86'928S MeteorGrey

Looks straight forward enough. I wish we could see inside the case while it runs....

Lizard928

Which side did you do it on? Rod to rod, or rod to crank?

Fabio421

I also had a conversation with Kevin Johnson where he reccomended this. I have wondered if there was more information somewhere. Thanks Tuomo.

When looking at different rod options for my upcoming engine build, I have seen alot of manufacturers offer to rifle drill the rod to feed oil from the big end to the small end. Is this mod done just to lubricate the wrist pin or is it done as some sort of piston cooling mod?

Lizard928

simple answer both.

ptuomov

Good point. Perhaps one could hook up a camera to the oil filler neck opening. I am not going to start installing lexan windows...

ptuomov

Both sides on all rods was the spec. I'll let you know what actually was done once the rods come back! ;-)

This will only turn into information once I run the rods in an engine and it either works or doesn't work...

We had Pauter drill those, and since they agreed to do it it's probably not completely idiotic. They charged $250 total for all eight rods, sixteen slots altogether. With hindsight, I should have ordered the rods directly from PPM with the slots and that would have probably added much less to the total price.

I know very little about the pressure oiled wrist pins. It's my (mis?)understanding that the spray out of the journal cools some but not much. That oiling mod is made to actually oil the piston wrist pin in engines that run high vacuum in the crankcase and control the windage aggressively. In 928 crankcase, the lack of windage is not a problem and I'll be running a wet sump so I opted not to have those oil channels feeding the piston wrist pin.

Someone with some actual knowledge about the piston wrist pin oiling, please correct the above if need be.

Kevin Johnson

I do not think the Audi technique (924) is as good -- it subtracts from the pressure gradiant in the shell and will introduce more oil into the windage cloud.

BMW uses a central slot on either side in the S-50.

All the slot does is to increase the probability that oil that has passed out of the bearing shell lands someplace useful. The net amount of oil released from the bearing is the same.

Porsche briefly had main fed oil squirters but withdrew them. One can surmize that they felt there was a need for them at the state of tune of that engine. However they were withdrawn because main fed squirters do introduce a net increase in oil. The slots will not. Very simple difference between the two. Note that Honda used BOTH the 16 slots and four main fed oil squirters.

There are more complex systems being used by other manufacturers. For example, in the old Nissan RB26DETT the main fed oil squirter is aimed into a passage in the underside of the piston crown for cooling. I looked up the patent on that design a few years back.

WallyP

I have speculated that one of the major causes for excessive blow-by and oil consumption on our engines is ring floatation due to too much oil on the cylinder walls. Perhaps tighter side clearances on the rods might help that...

Kevin Johnson

Side clearances on either side must be greater than the sum of the clearances on either side of the bearing shell border. If you restrict flow from either side it can have a negative effect on the temperature of the oil inside the shell -- the longer path to exit or the tendency to not exit and simply overheat.

slate blue

Wally for me it is the quantity of oil that the oil pump provides that is the problem, everything else is a patch up. Sure a race engine will use less oil through its oiling system because it has been optimized but a street engines that has a little more oil in the system can't hurt longevity. It is when you have a multiple of volume over an optimized engine that you start to get issues like we have with the 928.

Greg