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Sat Mar 05, 2022 2:04 pm

I've seem multiple threads on notching rods to direct the oil sling to help cool the pistons but no evidence as to whether or not it actually does anything. I've even notched a few on a couple builds if just for no other reason than trying something new.
since there isnt any evidence of it doing any good i guess this is just for the sake of discussion, but IF this notch did help direct oil wouldn't it be better if the cap was notched than the rod? I'd think more oil would reach a piston from an opposing cap then from the rod that piston is attached to since they maintain the same distance apart while the opposing pistons/ caps get pretty close to each other.
and the cap sees less stress than the rod , if your concerned about compromising the strength of the rod by filling a groove in it?

Sat Mar 05, 2022 2:15 pm

You need "evidence" for something that has in use 100+ million times all over the world for 100+ years? :P

Need to consider the side clearance and most of all the bearing oil clearance to estimate how much oil flow there will be.

Sat Mar 05, 2022 2:45 pm

Engine manufacturers have known about this for ages. All the major auto manufacturers have some rods that or forged with this gap for piston cooling.

As for notching the cap… not going to be as effective. Doing so would almost exclusively hit the underside of the piston. Notching the rod splashes both the piston and the cylinder walls. This is important because the oil on the walls effectively is pumped through the piston by the oil control ring. That flow of oil through helps cool the entire piston, not just the underside of the piston crown and pin bore.

Sat Mar 05, 2022 2:47 pm

I didn't ask for evidence I said that of all the threads about it there isnt any evidence to whether it does anything or not.
funny that out of the whole thing, THAT is what you choose to pick out of it..
golly gee beave, I wonder why new people don't post much on the Samba

Sat Mar 05, 2022 3:06 pm

The reason you don’t see the evidence here is because no air cooled VW hobbyist has the resources for such tests and measurements… apart from perhaps Jake Raby.

Piston developers and OEM manufacturers have the resources to both model and test the results of oil flow through and onto the piston. Long ago it was determined to be a simple effective solution. If there was no evidence of any benefits, OEMs wouldn’t bother adding this feature to rod forgings, or in more rare instances, actually machining ($$$) the feature post-forging.

Sat Mar 05, 2022 3:26 pm

Sorry I was a bit harsh, the word "evidence" tends to piss me off lately not just you.

In the 30's major engine manufacturers used high speed cameras to watch where the oil is actually going. And that's some neat stuff but probably not much on the internet.
I see it an old trick that's been pulled out now and then as needed.
The trend towards seeing pistons as being "oil cooled" even in small car engines is a more recent line of thinking.
And oil windage control thinking has changed too. in the 60's for instance the rear seal cavity has one little hole for the oil to drain back. If it were designed today I bet it would have multiple windows. Why? why not.
Less like an open box and more like a sponge with many passages to allow windage flow and oil return.

The beam side is always aimed at it's piston, the cap would be in line with the other piston a smaller % of time. Probably why subaru still just has the single notch on each side.
Maybe you can notch the cap one one side and the beam on the other, maybe better, maybe not, in any case it won't hurt.
I like how honda does it in the b18, don't have to think about which way it goes.

But it's just a little detail, only a tiny change. The bearing oil clearance and oil pressure and viscosity and rpm are the real factors in how much oil flows.
What should be discussed is bearing wall eccentricity, the LACK of it, or ignoring it. Even the bearing companies are a bit vague about it. Just "the clearance"...what clearance? Just the vertical? the average, or the average over the loaded zone or??
http://www.substech.com/dokuwiki/doku.php?id=oil_clearance_and_engine_bearings

Sat Mar 05, 2022 4:36 pm

I've always thought the notching the rods with the V groove was to supply the wrist pin with an adequate supply of oil needed especially in higher RPM's. I see no useful amount of cooling with the very limited amount of oil that will actually be sprayed on the bottom of the piston.

In my humble opinion, notching the rods is just another thing the high RPM racer do that has no benefit to a street driven engine.

Sat Mar 05, 2022 5:21 pm

vwracerdave wrote: I've always thought the notching the rods with the V groove was to supply the wrist pin with an adequate supply of oil needed especially in higher RPM's. I see no useful amount of cooling with the very limited amount of oil that will actually be sprayed on the bottom of the piston.

In my humble opinion, notching the rods is just another thing the high RPM racer do that has no benefit to a street driven engine.
Its actually more the other way around.

Sat Mar 05, 2022 7:16 pm

I happen to know a guy who develops pistons for big names… Mercury Marine, Chrysler, Polaris racing, NASCAR teams, and has consulted on F1 builds. He has forgotten more about pistons than I will ever know. Pistons are a whole lot more complicated than they appear, right down to the placement of the oil drain passage ways for the oil control ring. Most of his pistons have a different concentration of oil passages over the pin vs over the skirt to help even out heat transfer. This minimizes the amount of cold ovality that he has to build into tight tolerance racing pistons so they round out at running temp. The oil control ring itself doesn’t transfer a lot of heat to the wall, but the oil that flows through it can move a surprising amount of heat. Pistons live a hard life. Any heat they can shed is a good thing.

Sun Mar 06, 2022 7:38 am

Didn't at one time Porsche experimented with oil squinters to bathe back side of pistons with oil in attempt to cool pistons?

Sun Mar 06, 2022 9:42 am

Porsche did and there's several threads here of someone putting the Porsche jets into vw case. what I read said that the squirters were able to remove 100° from the pistons. how they figured that I don't know?
and that's really where I was going with posting this, that the V notch directing some oil makes sense to me but is it enough to really matter?
there was somebody on here that would machine squirters into the rod caps at one time but don't remember who now. I don't know how well that works but I thought the idea of opposing rod oiling the piston as it was close was a good idea.
I'm not saying anything is right or wrong and I'm not building anything, I just thought this would be a good discussion as this place has been pretty boring lately

Sun Mar 06, 2022 11:14 am

I used to have a service bulletin from VW for type 4 engines needing this mod, but can't find it now. Anyhow, here's some pics on how to do it.

Sun Mar 06, 2022 11:45 am

If there were proven benefits then I'm sure all rod manufactures would modify their rods to increase sales or provide more quality then their competitors.

I just don't see how this notch will direct very much oil to the pistons when oil has a 360* path to escape from the rod bearings thru side play clearance.

Sun Mar 06, 2022 12:07 pm

vwracerdave wrote: I just don't see how this notch will direct very much oil to the pistons when oil has a 360* path to escape from the rod bearings thru side play clearance.
I doubt that it changes how much spent oil that is thrown off the big end of the rod. What it does in my mind is give that oil a direction, a purpose instead of just a random spray. Puts it to work for you in other words.

Sun Mar 06, 2022 12:24 pm

That´s because you keep wearing blinders Dave. The notches, when added in the right angles, can shed quite a bit of oil towards the cylinder walls and the underside of the pistons. The goal is NOT cooling the pistons alone as it is also a matter of keeping the cylinderwalls wet at all times. By keeping the walls wet you can use the oil to remove more heat, and the - smaller - amount of oil that hits the underside of the pistons can reduce piston temps with 20- 25 Degrees C. according to Volkswagenwerk on a study of the type 4 engine.
This is for street engines, and especially those that work hard.
In a dragrace engine you should/would not do it. There you would want to REDUCE the amount of oil sling as much as possible to reduce drag, - including reducing the amount of oil going to the rocker arms to the bare minimum for said reasons.

So, on a street engine it is absolutely is worth it. I do it on just about all street engines, not just ACVW´s.
As for rod, - or car companies not doing it. - Porsche has done it since approx 1965. BMW modded the blocks for piston cooling on the M10 engine cirka 1971. Mercedes AMG engines got it from the get go with the W109 AMG, from 1970 I believe. Maserati had them already in the 3500 GT in the revised engine from about 1960. Ferrari played with it in the 70´s, but went with real squirters pretty soon.... Those are just the ones I remember on top of my head. So it is nothing new.

Sun Mar 06, 2022 2:16 pm

I think I would rather have it pointing down to keep the cam and lifters lubed.

eQ

Sun Mar 06, 2022 2:50 pm

When we turboed a motor we would grind the side/s of the rods to max. side clearance and file a small chamfer on the ends of the bearing inserts to form a 'V' to help feed oil to the sides and it kept the piston temps down verified by removing plugs after a boost run and sticking a temp probe on the piston top.

Sun Mar 06, 2022 6:11 pm

It's real and I do them with a ball end mill.

I was forced to watch actual WEEKS of footage as a bottom-shelf engine test cell engineer and I've seen enough high speed footage not to think twice. If I was building quality stock 1600cc engines and trying to make money I don't think I'd do it, but I have the luxury of caring about my engine at the expense of as much time as I feel like giving it.

My only other little hint is that having the notch in the center is almost certainly NOT optimal especially in a boxer config but I don't care enough about how little it matters to cut a hole in a case to put a camera in to figure it out, so I put them in the middle. Average RPM also affects where the oil tends to fling at (high or low on the piston, in our case) but figuring that out is a honorary doctorate's in itself, so screw it. You're getting 80% of the magic with the notch in the middle.

Sun Mar 06, 2022 7:08 pm

I see you have vices new than 80 years Mr. Jimmy :lol:

I notched the rods for my 1385cc. Because why not. If the notches are stealing oil pressure then you have a problem and need to check your numbers.

Or... just do what every modern manufacturer does and add piston squirters. Real ones.

Sun Mar 06, 2022 7:47 pm

earthquake wrote: I think I would rather have it pointing down to keep the cam and lifters lubed.

eQ

No need in a boxer with the cam below the crank. The cam gets loads of oil slung at it from the crank and also the pistons as they scrap the oil off the cylinders and back into the case…