- Sun Jan 22, 2023 5:31 pm
#196355
Back to this thread. Sorry for the long absence.
I haven't seen your motor, but it is possible that GB swapped the metal neck for a GTS neck. There were (at least) two variations of the GTS neck. You can identify a GTS neck because it has two ports next to the fill cap. The left-side port is the familiar one for the Y-hose (on S4 at least) that goes to both the air guide and tank vent electric valve. The right-side port, unique to the GTS necks has several different "uses" depending upon which factory breathing system was used.
The advantage of the GTS neck is that you can use the right-side port for breathing. Since it's much higher up the neck it's in a better situation for windage than ports at the base.
The integrated baffle in the plastic necks may or may not be a restriction.
Note that the metal filler neck has no integrated baffle at all. That neck used a separate baffle plate with an integrated non-replaceable o-ring. It's been NLA for decades. However, liberal application of Drei-Bond will do the job just fine.
... if you can also get a used plate.
I'd recommend both a metal-neck's baffle plate and the "deep" baffle. The former is a 'bit' of an AOS and the latter prevents liquid oil from getting thrown at the former which otherwise hinders it's ability to 'begin' separating oil from the foam.
First, let's deal with the last bit: Outside of corner cases, any effective means of air/oil separation is also a pressure restriction. Or, in other words, if you route big hoses to an AOS that can't handle the flow rate then the AOS hinders breathing.
Or, if you have several AOSs in series each one hinders flow rate. In that context AOS means anything the contributes to momentum change of the air/oil foam. It can be a 'grid' like in the ProVent or even a bend in a breather hose.
Back to the first: The oil drain should have gravity working in it's favor. The tube WILL be another breather. But, as long as breathing elsewhere is sufficient such that gravity driven oil flow overcomes any residual crankcase pressure then there won't be an oil back flow issue. Ideally, you wouldn't even need a check valve in the tube.
The proof of the pudding though, is a least 10s of seconds of engine operation at full load. That is a rather difficult test to do unless you're on a brake dyno.
Sterling's oil drain drains to the 16v factory location of the oil fill tube. The base of the tube is below the oil level when the engine's not running. When it is running the oil level is below the base. But, the location is far enough from the crank that windage isn't nearly as much an issue as it is above the crank and the oil filler neck port.
On 32v motors there may or may not be a "hole" at that location in the oil pan. Some of the "early" pans used on 32v motors just had a cover plate with a gasket over the port. Later S4 oil pans deleted the port entirely.
Sterling got himself an early oil pan.
It's also a vivid description of how bad the windage situation is at the hole for the oil filler neck: the crank is literally throwing liquid oil and oil foam up into the neck.
hernanca wrote: ↑Sat Jan 14, 2023 1:01 am I was also able to look under the oil filler neck (OFN). Unless the 86.5 came with a plastic OFN, the PO must have swapped in this plastic one that is there now. This plastic OFN simply had an integrated baffle and a built in restrictor on one of the base ports.Someone "stole" the metal filler neck. The metal neck was used until mid-'87.
I haven't seen your motor, but it is possible that GB swapped the metal neck for a GTS neck. There were (at least) two variations of the GTS neck. You can identify a GTS neck because it has two ports next to the fill cap. The left-side port is the familiar one for the Y-hose (on S4 at least) that goes to both the air guide and tank vent electric valve. The right-side port, unique to the GTS necks has several different "uses" depending upon which factory breathing system was used.
The advantage of the GTS neck is that you can use the right-side port for breathing. Since it's much higher up the neck it's in a better situation for windage than ports at the base.
The integrated baffle in the plastic necks may or may not be a restriction.
hernanca wrote: ↑Sat Jan 14, 2023 1:01 am I ordered an 85-86 metal OFN from 928 International and it had arrived at the shop, so I measured the heck out of it while there today (Edit: measurements added below). You were absolutely correct in indicating the top of the neck could not breath the equivalent of two 1" ID hoses! I measured the tightest area of the metal neck and it came out to 1.36 sq inches in area!And it's in a bad place with respect to windage.
Note that the metal filler neck has no integrated baffle at all. That neck used a separate baffle plate with an integrated non-replaceable o-ring. It's been NLA for decades. However, liberal application of Drei-Bond will do the job just fine.
... if you can also get a used plate.
I'd recommend both a metal-neck's baffle plate and the "deep" baffle. The former is a 'bit' of an AOS and the latter prevents liquid oil from getting thrown at the former which otherwise hinders it's ability to 'begin' separating oil from the foam.
hernanca wrote: ↑Sat Jan 14, 2023 1:01 am Additionally, the two base ports (no built in restrictor) = 11.5mm ID each.Those neck base ports are going to be filled with oil foam. With the metal neck, using only those ports, you'll not have a lot of breathing.
Calculating the area from these indicates the two ports combined equal the area of a 5/8 inch ID hose. (0.32 sq. inch flow cross section). I would like to take advantage of these ports as well, even though they are at the base of the OFN.
worf wrote: ↑Fri Jan 13, 2023 10:31 pm Of particular note though is the last "issue" of the oil drain. What I wrote previously was intended as a test of sorts. There's a fundamental flaw in what I wrote that appears if you go back to the 'super-stupid-simple' CC breather. add a big-enough AOS to it and give the resulting system some thought.
hernanca wrote: ↑Sat Jan 14, 2023 1:01 am But as I thought back again to the super-stupid-simple CC breather, I realized what you were probably getting at: with enough CC venting, there should be no CC pressure build up to speak of and so there should be nothing preventing the AOS's from draining into the oil pan, even if the drain tube is above the oil level. I realize you specifically said "big enough AOS", so I don't know if I will get full credit for this answer?Exactly correct and you get full credit.
First, let's deal with the last bit: Outside of corner cases, any effective means of air/oil separation is also a pressure restriction. Or, in other words, if you route big hoses to an AOS that can't handle the flow rate then the AOS hinders breathing.
Or, if you have several AOSs in series each one hinders flow rate. In that context AOS means anything the contributes to momentum change of the air/oil foam. It can be a 'grid' like in the ProVent or even a bend in a breather hose.
Back to the first: The oil drain should have gravity working in it's favor. The tube WILL be another breather. But, as long as breathing elsewhere is sufficient such that gravity driven oil flow overcomes any residual crankcase pressure then there won't be an oil back flow issue. Ideally, you wouldn't even need a check valve in the tube.
The proof of the pudding though, is a least 10s of seconds of engine operation at full load. That is a rather difficult test to do unless you're on a brake dyno.
Sterling's oil drain drains to the 16v factory location of the oil fill tube. The base of the tube is below the oil level when the engine's not running. When it is running the oil level is below the base. But, the location is far enough from the crank that windage isn't nearly as much an issue as it is above the crank and the oil filler neck port.
On 32v motors there may or may not be a "hole" at that location in the oil pan. Some of the "early" pans used on 32v motors just had a cover plate with a gasket over the port. Later S4 oil pans deleted the port entirely.
Sterling got himself an early oil pan.
Crumpler wrote: ↑Mon Jan 16, 2023 9:32 pm Essentially a billet cap with top removed welded to a rectangular box with the communication surface to cap cut out. There are several ridges welded to roof of the box, kind of like an egg carton effect.This is a good description of construction for AOS systems. You have to "catch" the oil foam but also provide a means for the oil to flow with a vector different from that of escaping gas.
The oil seems to blow straight up against the roof and gravity drip back down through neck. Vapor continues lateral through lines into second catch can.
It's also a vivid description of how bad the windage situation is at the hole for the oil filler neck: the crank is literally throwing liquid oil and oil foam up into the neck.
Hanlon’s Razor: Never attribute to malice that which is adequately explained by stupidity.
Heinlein’s Corollary: Never underestimate the power of human stupidity.
The Reddit Conjecture: Sufficiently advanced stupidity is indistinguishable from malice.
Worf’s Razor: Never attribute to stupidity that which is adequately explained by laziness.
Worf’s Identity: Sufficiently advanced laziness is indistinguishable from stupidity
Worf's Law: Once you've mitigated risk from stupidity and laziness in your endeavors, failure is usually the result of insufficient imagination.
My 928 Inspection Guide
Heinlein’s Corollary: Never underestimate the power of human stupidity.
The Reddit Conjecture: Sufficiently advanced stupidity is indistinguishable from malice.
Worf’s Razor: Never attribute to stupidity that which is adequately explained by laziness.
Worf’s Identity: Sufficiently advanced laziness is indistinguishable from stupidity
Worf's Law: Once you've mitigated risk from stupidity and laziness in your endeavors, failure is usually the result of insufficient imagination.
My 928 Inspection Guide