Actually, because it's been done successfully since the 1970s there is a HUGE body of data that supports it's success. You just will never find it

It seems to be a recent phenomenon that historical data and experts are getting challenged in a way that is impossible to defend. You can't provide data because there was no means to record it like there is today. So the absence of the (undocumented by today's internet standard) information MUST mean it is totally unbelievable.

Sad really. It's so much easier to consult history and experts, than recreate it.

I just wish I had seen this post before I buttoned up the bottom end. It would have been very easy for Armondo at CCR to cross drill while he was welding my crank. Too late!! Darn.

Said you. Hilarious.

When the guys who have been doing this for forty plus years, the guys who build the best, hardest ridden motors on the planet condone something, you should listen. Unqualified platitudes are silly.

Perhaps this doesn't fly for Nissans given your assertions and alias, but in Porsches, it's all good.

Cross drilling can be quite effective if it is done properly and crank designers have the situation under hand, I am sure companies like Braynt Crank have great designs and solutions. The problem with all due respect to to the science of tribology is to ultimately cool the bearing with an adequate supply of oil.
It can be a shock to some folks to realize that a lower oil pressure can be beneficial if it is the result of more clearance, clearance has solved more bearing problems than modifying passages, to much clearance is always better than to little. Ask any serious engine builders the conversation can be very interesting.

Of course, but ...

perhaps the Porsche experts can throw us neophytes a bone to chew on.

What's the physics and best practices behind the mod ?

^^^

Pmax, if you do a search in this forum for "crank cross-drilling" (different than "Kenik's cross-dressing" :eek:) , you will find plenty to read on the physics and best practices.

PS - that nismo dude doesn't know what he's talking about.

I think the physics behind this particular mod is pretty basic: at high rpm, the flow of oil to the middle of the crank is less than needed to offset the heat and bearing load.

We are fine at 6500 rpm. But these guys are pushing past 8000 rpm.

So the physics are: add a source oil oil pressure to the middle of the crank. Thus
It is easier to get oil pressure along the whole crank.

I think you have to think about the 911 crank. It is a 7 bearing main. Long! And 8 journals plus 6 rods to feed. Lots of oil needed.

So experience with failed 2/5 bearings in race engines showed the need for more oil. Simple observational learning. Simple fix actually. Just not needed for street engines kept to reasonable rpm.

One other aspect of the physics part. At high rpm the centrifugal force acting on the oil in the crank can force the oil out at a rate that may exceed the stock pump's capacity, esp. when running clearances on the high side.

Also the physics of just moving the oil.

Getting the oil to change from a pure radial flow in the case, to circular flow in the gap, and then jumping to a rotating crankshaft, with centrifugal load from the oil column increases the losses as rpm go up.

More flow and pressure help. So does a "shortcut" with an added supply in the center. As long as the pump can keep the pressure high, while satisfying the flow rate it seems to be a good thing.

The majority of the problems associated with Porsche racing engines and Street based components that are used in the majority of cases is that the matching of revs and the appropriate braking are sometimes at odd with one another. This throws the Rod assembly into a tensile not a compression situatation and the big end of the rod is no longer as round as it is intended to be, that is why eccentricy clearance is built into the brg. If stock clearances are used even when the eccentricy and cross drilling is employed the big end of the Rod will swipe the journal and trouble starts disaster ensues that is why Engine builders use between .0007 and .001 additional clearance on the journals. And all this is a little more intensified by the center two Rods being the last to get supply, it started with Ritchey Ginther who used to have Harold die grind nothches at the parting lines to use the 2.0 911 stock crank and rods to retain oil and it is still true today.
The GT3 RSR are cross drilled and have a essentailly a cross drilled or two larger holes at the very front of the crank in the nose bearing and generous clearance but are other than that are pretty stock in apearance with out groving mains and knife edging etc. I don't understand why someone would weaken a shaft by undermining the area that receives the Torsional excitation.
But never the less these practices have apparently helped builders and reduced the amount of measuring necessary for a sucessful power plant.

regards

El... oh.. el

^ could it be because the cranks work so well they don't removed all that often? Could be...

There's 8 bearings! Compare to your average American V8 that only has 5 bearings, the H6 is plenty robust.

LOL, I sent a crank for polish and it came back polished and drilled

Rob, how many miles have you put on this engine (post #7)? If it were me, I would be worried about the size of the hole compared to the others. It looks way bigger. But if you've run the thing 200k miles, then obviously somethings are entirely over thought (me).

The hole is larger to promote additional oil flow to the #4 main bearing.
All other holes are just feeding a single main journal/bearing where the #4 hole is flowing additional oil to feed the adjacent (#2 & #5) rods.
The feed hole is probably slightly larger than it needs to be but I really don't see a down side.

Thanks Henry.

Can someone provide roughly what this costs?

I may groove the bearings myself. I like the jig posted. :cool:

Never mind, I see Ollie's charges about $130. Not bad.

In case you're curious, the thread linked below includes some pictures to indicate what goes into cross drilling the crank

http://forums.pelicanparts.com/911-engine-rebuilding-forum/582197-another-crank-cross-drill-question.html

I wanna know what a "NISMO" type is doing on a Porsche forum.

Trying learn something about SUCCESSFUL race cars maybe.


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