Oil restrictions / larger drains for journal bearing twin turbos

[MMP]

I would like to start a discussion on oiling of twin turbos.

In the past few months I have had 3 CHRAs (out of about 600 shipped in the past 1.5 years), where the customer reported the turbos were smoking. I told him to send them in and I will Take a look at them and if anything had failed I would warranty repair the turbos. I got the turbo back and sure enough the turbine housing had oil in it and it was leaking past the seal. On full teardown, inspection and measurements, it was found all the internals were perfect, thrust bearings were perfect with no in and out play, journal bearings were perfect and the radial play was in spec. Compressor side seal seat and seal perfect, turbine side seal seat and seal perfect. Shaft was perfect, orings perfect, all perfect. Also oil was found leaking out the compressor side seal as well. It was clear the turbo was leaking because the bearing housing was not draining adequately. There was some issue with the car not allowing the turbo to drain adequately.

So what could cause the turbo to not drain adequately? Here are some possible culprits:
1) crank case over pressure - the crankcase vent is not freely flowing or there is a PCV valve leak under boost or too much blow by on the piston or something else is causing the crank case to not exhaust fumes quickly enough and it overpressures slightly causing the oil in the bearing housing to back up some because it can no longer drain freely causing the oil to leak past the seal.

I want to take a moment here to clarify the turbine seal and compressor seal in the CHRA (compressor Housing rotating assembly) is a metal to metal seal ring with an end gap, much like piston rings on an engine. It is not designed to seal oil backed up against and especially not oil backed up against it and under any sort of pressure. The metal seal functions as a splash barrier to keep oil in and a wiper seal.

2) inadequate oil drain - there is some issue with the oil drain such as collapsed, kinked, or not big enough diameter, and as a result oil gets backed up in the bearing housing.

3) Too much oil pressure/oil supply - The car is producing too much oil pressure and the drain isn't big enough to handle the return flow and oil backs up in the bearing housing,

Now there has been a ton of discussions on number one above over the years across all N54 forums but not enough productive discussions I think on number 2 and 3 above. RB has done some discussions on 2 above and offers bigger oil drains but some other vendors have been pretty negative about discussing this at all which is weird to me because oil drains and restrictor sizing is a common discussion in other turbo platforms.

Some notes on The internals of the journal bearing TD04 turbo. The Turbo has 1.75mm internal oil passages for each journal bearing and also a 1.75mm passage in the thrust washer. Upgraded thrust washers like the ones in MMP turbos have 2x 1.75mm passages to increase the oil supply to the thrust washer which also creates more oil return line flow. On the outlet of the bearing housing its a 13.5mm hole connecting to the drain line.

On the engine in the block its a 13mm hole for the return line. The stock oil lines are 12.5mm metal tubes with a flexible section in the middle (prone to collapse and kink due to how short the section is and awkward angle). The short flexible section in the middle, not exactly sure what ID it is but probably around 13-14mm ID.

TD04 turbos have been around for a long long time (decades) and used on many platforms and discussed in many many forums over decades. General results from shared experiences is that a 16mm ID oil drain is required and if too much oil supply a 1.5mm oil restricter can be used on the oil supply side. Many Many people have had alot of success applying this criteria when they have had oil leak issues and have addressed possible crankcase vent issues already. 1.5mm restrictor size has proved to be very effective and solve over supply issues in the TD04s in EVOs, Miatas, and Subarus, do some searching online and you will see. Now not everyone requires this but after exhausting all possible issues with Crank case pressure vents and oil drains, if you still have problems than a restrictor should be used. Even Garrett makes this recommendation in the technical section of their site. Also what has been found to work good for a drain size is a 16mm ID line which is the same size as a -10AN line, but the fittings on a 10AN line that you buy on ebay many times have an id of 10mm fir a -10AN fitting, not all fittings are the same ID and varies by who makes it so YMMV. Also Ball bearings run about a 1mm restrictor and have less of an oil drain requirement for that reason. Journal bearing turbos and especially those with upgraded dual port thrust bearings require much more oil drain size that a single ball bearing turbo because of the amount of oil flowing through the unrestricted journal bearing turbo.

Here is a good video by turbolab that has dealt alot with this issue on turbo repairs with improper drain size.

Now generally you want to tackle the problem first on the oil drain side and maximize the oil flow. I've studied the ports and geometry and the biggest I could design was an adapter fitting at the block with a 15mm ID that connects to 19mm hose (3/4in ID hose) and a 15mm adapter fitting for the turbo oil drain connection. Now before you say, why would you use a 19mm hose on a 15mm ID fitting with 13mm ID connections on the Block and turbo, I can guarantee you this, a 13mm ID line from turbo all the way to block will flow alot less than than a line with 15mm fittings on the ends and the whole hose section at 19mm ID. I cant take the time to explain that but if you dont believe do some google searches on fluid dynamic flow losses in pipes and you will see for yourself. Remember we are not dealing with choked flow we are dealing with reducing head losses to minimize flow restrictions for free flow.

I also took a look at the supply side and designed an oil restrictor that fits nicely into the end of the oil supply line without changing any of the bolting geometry and has a 1.5mm orifice restrictor in it.

Now on the oil supply issue I also had a discussion with a reputable shop today where we discussed that the N54 produces excessive oil pressure and couple that with thick 40W oil when warm and sometimes people run 50W oil, pressures get pretty high compared to normal.

Attached pictures are of the stock oil return lines, the oil return fittings I quickly designed today, and the oil restrictor I also quickly designed today

in case the question comes, I will answer it now... if I do decide to make these oil drains and oil restrictions, they wont be expensive, they will be pretty inexpensive and affordable, not trying to brake the bank here with some simple fittings.

OK now lets have a productive technical discussion on topic. thanks.

 

[QuantumGravity1]

Thanks for the tech info. I’ll be interested to hear this discussion as it develops. I will be firing up my car with a set of MMPs tomorrow night or Thursday.

 

[MMP]

Another thing that can happen if the bearing housing is not draining properly is that over time the problem compounds and becomes worse. How this happens is at first you are having a leak and smoke, then every time you shut off when hot and with the leak the oil cokes up on the heat shield underneath the turbine wheel where it leaks out the turbine seal. As that carbon builds up over time it can throw the turbo out of balance causing a very bad failure or closing the design gap between the turbine wheel and bearing housing with built up carbon layers from the coking. So not addressing the issues does cause the issue to become worse over time and can get really bad over a longer period of time.

 

[BMWE92_Harry]

I would be interested in the oil drains. So currently only RB makes the upgraded drains?
With the excessive blow by, basically customers would need a new engine before they install new turbos? I’m assuming VTA would help, but won’t eliminate the blow by.

 

[QuantumGravity1]

So I guess the question is, for a guy who is just about finished installing a set of MMPs, what actions should I take? I have all new oem oil lines and drains, I would bet my life there is no kinks in either drain line, and I have a properly operating pcv system. Am I good to go? Or should I order some RB high flow oil drains or another brand? Or take any other actions? Thanks in advance for any info guys.

 

[MMP]

RB drains are definitely better than OEM drain lines. If you can return your OEM drain lines I would do so and get the RB units.

Maybe in the future I will produce mine, who knows.

 

[mfractal]

Great discussion. Following

 

[ShocknAwe]

Hmm. What kind of flow increase and nominal pressure reduction at the oil seal would we be seeing if a 15mm fitting and 19mm line are used? Thinking back to college physics that 13mm drain would just create a little turbulence, but without major flow drop. But would the increase in flow from the larger fittings actually be significant?

 

[Biggenz]

Have you tried using a smaller oil restrictor?

 

[chadillac2000]

So 3 sets of your turbos out of 600 you've deemed needed upgraded drains while the other 597 did not?

 

[Rob@RBTurbo]

Very nice production rate there! RB does around 250-350 N54 units (Note: Half that for sets) per year and I tell you it is enough to make you wanna jump off a bridge sometimes!

Regarding your concerns:
1) Overpressurization of crankcase-
A. PCV system. Cheapest and easiest fixes here and we all know them and no need to discuss. Simply get them done.
B. Engine Issue. Do compression test or better yet a leak down. Ideal leak down rates are sub 10%, many really healthy N54's cylinders leak down are 2-5%. Over 10% is eyebrow raising and over 15% likely going to cause issues, so pray for low numbers but do the tests properly as to get accurate data. An issue here is not going to be fixed by anything aside from a new engine or engine build.
2) Oil Drains-
A. The OEM units can suffice despite small size and poor flow routing and to complicate things they can be defected during R&R, but if careful however they are quite resilient and certainly high quality. However a kink is not good and the overall design of their routing isn't the best, but once again they can get the job done. Size wise they are around 13mm ID at their largest points but taper to nearly 11mm ID at their smallest points. In our opinion they work but our high flow drains are better and it never hurts to have a better drain.
B. The RB High Flow drains are 14.5mm ID at the fittings (this is the max size you can use due to the O-Ring groove that goes into the block) and the hose ID itself is 16mm. They are a direct straight shot to the pan. Truth be told they can not be made any better without modifying the engine block, there are some minor caveats to these in that they OEM units install a bit easier. Just to note we reduced the price on these yesterday to $190 for the set, ironically enough to this conversation.
3) Oil Feed Supply/restriction-
Unless you have some defect in your cartridges they have restriction built into them. Oil Restrictors are not needed for any JB turbos. We do not use them and for quite a long while now of production have had no smoking issues.

Any other faults could simply be in the build, or build quality, of the turbocharger itself.

Rob

 

[Tony@VargasTurboTech]

Mauricio, Can you do us a favor, throw a set of your CHRA's on your high-speed balancer, and tell us how much oil flow is coming out of the drain at 200K RPM at 40-80PSI going up in 10 psi increments. I am curious if your results will match ours. After you do that, take the restrictors you had made 2-3 years ago with various orifice sizes that fit into the oil feed of the bearing housing, and then retest the oil flow at 200K RPM, at varying pressures from 40-80PSI again in 10 PSI increments. At that point, you should have come to the conclusion we did, that unless a stock drain is plugged there is 0% chance it would cause smoking on a properly built UNRESTRCITED N54 CHRA.

You see, this is all testing we did in house 2-3 years ago when developing N54 turbos. There are numerous reasons an N54 will smoke, and leak oil. The oil drain size is not a factor on a properly built unit. It is oversized to a point it could handle twice the flow the N54's put through it, and not be a restriction. We sold over 1000 N54 turbos in 2017, near 0 reports of smoking or oil leaks. The biggest thing we dealt with is poorly cast turbines which were a headache. Our solution was to have new molds made, and have our own wheels cast to the specs we were looking for, out of the material we wanted. Problem solved

If you want the CAD drawing for the restrictors, or if you want the 200 or so I have sitting here I will never use because they do not help anything, I will sell them to you very cheap...

Can we kill this "high flow drain" discussion already. The Stock drains are sized between -8, and -10 AN lines. Much closer to -10. A -10 line can drain a GIANT single journal bearing turbo with no issues. Let alone a respectively TINY TD03 or TD04 MHI. I mean if people are looking to spend an extra $225 for something that does nothing. Congrats to Rob for good marketing. Outside of that if you are looking to solve smoking issues with a bigger hole to drain your N54 turbo, you either have mechanical problems you ought to address, or the turbos were not built properly to start with. /thread

 

[veer90]

Hmm. What kind of flow increase and nominal pressure reduction at the oil seal would we be seeing if a 15mm fitting and 19mm line are used? Thinking back to college physics that 13mm drain would just create a little turbulence, but without major flow drop. But would the increase in flow from the larger fittings actually be significant?

Highly doubt there would be turbulent flow, considering how viscous motor oil is even at operating temp. Unless the flow rate is crazy high I think it'd be safe to assume laminar flow

 

[mikeseli]

Mauricio, Can you do us a favor, throw a set of your CHRA's on your high-speed balancer, and tell us how much oil flow is coming out of the drain at 200K RPM at 40-80PSI going up in 10 psi increments. I am curious if your results will match ours. After you do that, take the restrictors you had made 2-3 years ago with various orifice sizes that fit into the oil feed of the bearing housing, and then retest the oil flow at 200K RPM, at varying pressures from 40-80PSI again in 10 PSI increments. At that point, you should have come to the conclusion we did, that unless a stock drain is plugged there is 0% chance it would cause smoking on a properly built UNRESTRCITED N54 CHRA.

Tony, the high-speed balancer does not represent a real world scenario. The drains are subjected to various crankcase pressures which is not representative on this balancer. The drains to work as intendent need to have a volume of air in them, in other words if air is somehow choked in any section of the drain line's length this will impede the drain from flowing as much as it was intended to.

 

[Tippin]

Tony, the high-speed balancer to does represent a real world scenario. The drains are subjected to various crankcase pressures which is not representative on this balancer. The drains to work as intendent need to have a volume of air in them, in other words if air is somehow choked in any section of the drain line's length this will impede the drain from flowing as much as it was intended to.

Not to be a dick but you are kind of helping his argument,if you are seeing positive crankcase pressure then you should fix that first. At that point drains are not the problem but rather the crank case. The only other scenario I can think of is displaced oil under high lateral G's coming up to block the ports but I do not think that is possible on this motor.

Tony has more data than any other vendor out there so far. So do you buy based on speculation or raw data? I will admit that RB drains can add safety by eliminating some common fail points such as kinked or degraded lines but to say that oe lines can not drain oil properly is pure speculation.

 

[mikeseli]

Not to be a dick but you are kind of helping his argument,if you are seeing positive crankcase pressure then you should fix that first. At that point drains are not the problem but rather the crank case. The only other scenario I can think of is displaced oil under high lateral G's coming up to block the ports but I do not think that is possible on this motor.

Tony has more data than any other vendor out there so far. So do you buy based on speculation or raw data? I will admit that RB drains can add safety by eliminating some common fail points such as kinked or degraded lines but to say that oe lines can not drain oil properly is pure speculation.

I think the “dick” is the guy that does not understand what I’m saying. A VSR balancing machine will drain the oil through its CHRA drain port, typical no drain hose is attached, even if one is to be attached it is not representing a drain on a running engine.

 

[Tippin]

I think the “dick” is the guy that does not understand what I’m saying. A VSR balancing machine will drain the oil through its CHRA drain port, typical no drain hose is attached, even if one is to be attached it is not representing a drain on a running engine.

I know exactly how a VSR works sir and my point is that based on the data we have there is no argument. Tony has the most data. Volume of oil produced at a specific PSI can be used to estimate flow through a hose if you know the diameter and angle of bends.... or you could just used cad and fluid dynamics if you access to it.

Once again you are just making yourself look silly. "even if one is to be attached it is not representing a drain on a running engine it is not representing a drain on a running engine"... No one here has hooked up a pressure sensor to an oe drain line to see if there is positive pressure. Whats the next best thing? Oh that's right using a vsr balancer to get an estimated flow.

You are arguing with the one person who has the most data... is it perfect no but please feel free to name any other vendor that has more data then him at the moment... I'll wait for it.

 

[mikeseli]

I know exactly how a VSR works sir and my point is that based on the data we have there is no argument. Tony has the most data. Volume of oil produced at a specific PSI can be used to estimate flow through a hose if you know the diameter and angle of bends.... or you could just used cad and fluid dynamics if you access to it.

Once again you are just making yourself look silly. "even if one is to be attached it is not representing a drain on a running engine it is not representing a drain on a running engine"... No one here has hooked up a pressure sensor to an oe drain line to see if there is positive pressure. Whats the next best thing? Oh that's right using a vsr balancer to get an estimated flow.

You are arguing with the one person who has the most data... is it perfect no but please feel free to name any other vendor that has more data then him at the moment... I'll wait for it.

I give up arguing with people that can not comprehend.

 

[Dmak]

I think the point mikeseli trying to say is, running the turbo on a balancer with oil flowing does not show the complete picture of how the turbos runs, oil pressure changes, crankcase pressure changes like in driving conditions.
Since we have a high and low pcv system, the switch over point would be betweem vacuum and boost. Also the oil temp, brand of oil, etc are also all variables. While the test shows the amount of oil coming out of the chra at xxxxxx rpm, it wont show real driving conditions as rpm goes up and down between shift, engine switching between vacuum and boost, etc.

Anyway. Here is my take. I agree, the bigger and least angle of the drain is always better. Now what size is needed is the disagreement we have between vendors.

So my question would be, whats the drain size of those running a big single with 30+psi? Do they have problem with oil pushing out their turbo? I would assume, those single turbo kit would come with a bigger then stock drain hose, but at then end still using the one factory drain port at the side of the block.

 

[Tippin]

I think the point mikeseli trying to say is, running the turbo on a balancer with oil flowing does not show the complete picture of how the turbos runs, oil pressure changes, crankcase pressure changes like in driving conditions.
Since we have a high and low pcv system, the switch over point would be betweem vacuum and boost. Also the oil temp, brand of oil, etc are also all variables. While the test shows the amount of oil coming out of the chra at xxxxxx rpm, it wont show real driving conditions as rpm goes up and down between shift, engine switching between vacuum and boost, etc.

Anyway. Here is my take. I agree, the bigger and least angle of the drain is always better. Now what size is needed is the disagreement we have between vendors.

So my question would be, whats the drain size of those running a big single with 30+psi? Do they have problem with oil pushing out their turbo? I would assume, those single turbo kit would come with a bigger then stock drain hose, but at then end still using the one factory drain port at the side of the block.

I agree with that 100% and the point I was trying to make was that no one has actually tested this to confirm if there is truly a restriction. Tony is presenting us with more data than anyone else here and that has substance. It may not be real world data but it is the better than anyone else has done. If real world data was that easy to obtain then people would have done it ages ago, the next best thing is to simulate as best as possible. So why argue with the person who has brought the most to the table?

I hate when people bash the vendors who take the time to test shit. Mikeseli is pointing out the obvious. We all know the test does not take everything into account BUT it is the next best thing and no one has more to offer.

PS RB makes a great product that adds some piece of mind ( no kinks or deterioration) but I think it is safe to say that properly installed and good condition oil drains will work well for anyone.