BMW S65 VANOS hub cover options (all inclusive).

[BenFenner]

I wanted to copy my post from another forum to this one, but this forum does not support tables, so I'm just linking to the original:
BMW S65 VANOS hub cover options (all inclusive).

This also makes things easier on me, as I have countless (hundreds?) of threads like this and when I have to make an update, it's so much worse if I have to apply that update in multiple places.

If anyone has weights for any of the VANOS hub covers that I don't, I'd love to get that info.

[BenFenner]

For the record, I purchased Slon covers back in 2022-01-05 when they were the only option (for much more than they sell for now) knowing I would have to painstakingly knife-edge them over the course of maybe 4 days to mitigate the windage issue.

Well, it took me well over 3 years to get around to installing them, and by then there were much better options available. I picked up some Evolve units and installed those instead (and plan to sell the BNIB Slon units). I'd have been just as happy with Ventrax units as well.

May your oil pick-ups be ever free of debris.

[drwankel]

Why post this info on a Nissan forum?

[BenFenner]

Originally Posted by drwankel

Why post this info on a Nissan forum?

Did you read the first sentence?

Ehhh, maybe that doesn't answer the bigger question.

So that particular Nissan forum (The SR20-Forum) is the most trustworthy, user-centric automotive forum there is. It is user-supported so there is no admin/mod oversight as to which vendors can be mentioned in threads, or compared, or given favorable reviews, etc.

I have had huge issues in the past with other forums (BMW ones are notorious) for stomping on my work when forum sponsors are involved (or not involved, or not involved "properly"). You can read more about some of that in the History section of the Z3 Manifesto:
https://www.sr20-forum.com/general-n...s-and-diy.html

There is no way a thread like this could exist on any of the common BMW forums as they are currently set up today, nor in the past. Maybe this thread will last longer if the offending data is off site...


Edit: And boy is it nice that this info is hosted on a forum that works properly on all modern browsers, doesn't go off-line for days at a time, doesn't suffer from database response errors, general slowness, and doesn't blanket block IP ranges causing users to need VPNs just to get work done here.

[drwankel]

Originally Posted by BenFenner

Did you read the first sentence?

Ehhh, maybe that doesn't answer the bigger question.

So that particular Nissan forum (The SR20-Forum) is the most trustworthy, user-centric automotive forum there is. It is user-supported so there is no admin/mod oversight as to which vendors can be mentioned in threads, or compared, or given favorable reviews, etc.

I have had huge issues in the past with other forums (BMW ones are notorious) for stomping on my work when forum sponsors are involved (or not involved, or not involved "properly"). You can read more about some of that in the History section of the Z3 Manifesto:
https://www.sr20-forum.com/general-n...s-and-diy.html

There is no way a thread like this could exist on any of the common BMW forums as they are currently set up today, nor in the past. Maybe this thread will last longer if the offending data is off site...

Had no idea. Been in and out of car forums for the past 25 years, and haven't visited that place. Thanks for the explanation!

[a5m]

This is all very fascinating and eye opening for me. Thanks for putting this together and sharing it with the community.

How are you ranking the oil behavior of the clip on covers? Are you comparing them visually to the stock units? Given the history and importance of oil in the S65, it seems oil behavior should be considered closely with windage?

I like to not stray too much from OEM design, as credit should be given to the time and effort put in by the engineers. With that said, it seems the closest to the stock design would be the superior choice, leaving us with Ventrax and TPE. Billet appeals more to me than 3D, so I'm heavily looking into switching to the Ventrax solution from my originally planned Mporium route. Saving me the time and effort of timing is an added bonus.

Chrisyphus Curious what Partee's opinions are on all this?

[BenFenner]

Originally Posted by a5m

How are you ranking the oil behavior of the clip on covers? Are you comparing them visually to the stock units?

Great question. Yes, I am just looking at the pictures of the units availabe online and comparing them to stock. (Well I have also seen the stock units, the Slon units, and the Evolve units in person.)

The stock units have two very specific voids/holes in them, in very specific places, and the covers are then very specifically solid everywhere else. It is my guess that this may be important to control lubrication and oil behavior with regard to the VANOS hub springs. Not too much oil is allowed in/out, and not too little. And the oil that is allowed in/out travels through a specific path. I suspect with the hubs in motion that oil is mostly entering through the center hole and exiting through the outer hole found near the spring pins. The spring windings itself acting as a long path for the oil to eventually travel along to cleverly lubricate the entire spring. If someone is installing the Ventrax, TPE Precision, or similar solution they should take care (if not forced to already by the design) to place the outer hole at the spring pin location for this reason (and balancing reasons).

With all that said, the best oiling of the spring doesn't seem nearly as important to me as windage (although I guess it is partially related) or the mass/inertia of the covers, so I would prioritize accordingly. But of course that is just one man's opinion.

Originally Posted by a5m

I like to not stray too much from OEM design, as credit should be given to the time and effort put in by the engineers. With that said, it seems the closest to the stock design would be the superior choice, leaving us with Ventrax and TPE. Billet appeals more to me than 3D, so I'm heavily looking into switching to the Ventrax solution from my originally planned Mporium route.

Given your priorities, that makes perfect sense to me. However just as I was prepared to knife-edge the Slon covers (before there were other options) you too could consider drilling an outer hole in the Mporium covers if you already have them in hand. But then you might also have to drill some center holes...

But as mentioned earlier, I personally value less windage much more than the oiling situation, so I probably would not modify them at all if they were in my hands. (I might try to sell them and pick up the big CarBahn washers...)

However, if you are prepared to move from a bolt-on solution to a clip-on solution, it makes perfect sense to go with the Ventrax solution given your proclivities. And I wouldn't try to convince you otherwise.

Sorry, it's quite the balancing act for me, but I hope you follow what I'm saying.
And I should stress that in many ways I am splitting hairs and nit-picking. But that does seem to be my super power, and it is how I can make decisions I am happy with (and likely remain happy with in the future) when there are many options available.

Originally Posted by a5m

I like to not stray too much from OEM design, as credit should be given to the time and effort put in by the engineers.

Sure, but don't forget they are the ones who gave us the flawed design to begin with*. And recognise they only really have to worry about things mostly lasting through the warranty period and have much more incentive to shave costs wherever possible. That is an engineers job after all--to make a bridge as cheaply as possible given the constraints. We as enthusiasts modifying our cars of course have different motivations and budgets. We should learn from them where we can, but they are not gospel.


*Okay to give them the benefit of the doubt, maybe the engineer(s) intended the stock covers to be replaced with the valve cover gaskets, but upper management at BMW decided not to issue a part number for them on their own.

[omgzirra_exe]

lel, im also a member of that SR20 forum, as i'm from a Nissan background also.

[a5m]

Originally Posted by BenFenner

Sure, but don't forget they are the ones who gave us the flawed design to begin with*. And recognise they only really have to worry about things mostly lasting through the warranty period and have much more incentive to shave costs wherever possible. That is an engineers job after all—to make a bridge as cheaply as possible given the constraints. We as enthusiasts modifying our cars of course have different motivations and budgets. We should learn from them where we can, but they are not gospel.


*Okay to give them the benefit of the doubt, maybe the engineer(s) intended the stock covers to be replaced with the valve cover gaskets, but upper management at BMW decided not to issue a part number for them on their own.

Firstly, I'm a champion of nitpicking also, so you summed it up nicely about feeling good about a decision when one goes into that level of detail

Thanks for answering all my questions. Yes I did notice the openings in the covers and wondered if it'd be best to install them in a particular orientation to maintain stock like oil flow.

I follow what you're saying. So that makes me wonder, how did you determine the windage rankings when comparing to stock? I noticed while the other columns had a 'Stock' designation, Windage did not. Is None equal to Stock? Or is that undetermined so the rankings are best estimates?

[BenFenner]

Originally Posted by a5m

how did you determine the windage rankings when comparing to stock? I noticed while the other columns had a 'Stock' designation, Windage did not. Is None equal to Stock? Or is that undetermined so the rankings are best estimates?

More good questions.

The stock unit has some windage, just a little mainly due to the outer hole.

"None" is less windage than stock. I will edit the list to make this clearer. I kind of knew this part was a little confusing and hoped to improve it later.
The reason I didn't label any other units as "Stock" and instead labeled them as "Low" is because nothing has exactly the same windage as stock, since nothing else has the outer hole in the same place AND has a completely smooth outer rim. Anything with a stock-like hole also has some small slits cut out of the outer rim at the least.

I am estimating the amount of windage based on images I've seen and physical copies I have felt. The material thickness almost always comes into play, and then of course the shape.

The worst windage is going to come from most of the units on the outer diameter where they are necessarily not smooth and moving the fastest. The Slon units and ones like it really suffer here. They are little fan blades sticking out into the wind. The Evolve units are almost smooth here, so only suffer a tiny bit. The Mporium units are smooth here, so really suffer no windage from this area.

Then I look at the transition where the material transitions from the outer diameter to the flat face. This is where the next most intense windage is going to come from. If there are protrusions or a hole there then there will be some additional windage. The stock units have one hole here on the outer corner, and thus have a little bit of windage.

Next importantly I look at the face itself and if it has windows taken out to create spokes like a wheel and assume there will be a good bit there, especially if the material is thick. The Slon units again are really bad here.

Finally I look at the center and if it is open to allow for a tiny bit more windage, or completely closed. This is the least important place, but still pays a factor.

I certainly have not performed tests or anything to make these determinations, but I am confident in my ability to make these educated guesses. Take that for what you will.

(I have added most of the above to the thread to help explain things further, and made it clearer that I rate the stock units as "Low" windage.)

[a5m]

Bought the Ventrax covers. Weight 34g each. 6082-T6 aluminum, not 6061, and made overseas. Anodized for hardness and corrosion resistance.

[BenFenner]

Thank you so much a5m for the information on the Ventrax covers. I've updated my thread with the mass of the Ventrax units, and the material used.
I had a source for the 6061 spec from an obscure blog post they made but I can't find it anymore (or maybe it was for another design, they are blending together a bit in my memory) so I'll go with what they told you.
In the process I noticed I had the material spec for the Evolve covers wrong as well, so I've updated that (from 6061 to 6082).

[a5m]

Originally Posted by BenFenner

Thank you a5m for the information. I've updated my thread with the mass of the Ventrax units, the material used.
I had a source for the 6061 spec from a rare blog post they made but I can't find it anymore so I'll go with what they told you.
In the process I noticed I had the material spec for the Evolve covers wrong as well, so I've updated that (from 6061 to 6082).

I experienced the same when doing Google searches, in the search results I'd see '6061' mentioned but clicking on the actual link, I'd see no mention of it. Maybe they initially used 6061 then switched? In any case, that's what they're claiming now.

You're right, Evolve uses the same material, that's why it stuck out to me when they said they use 6082. Hoping the engineers here give some insight into that particular alloy's characteristics. I wonder if the deformation concerns mentioned by Chrisyphus still hold.

[Assimilator1]

Originally Posted by BenFenner

More good questions.

The stock unit has some windage, just a little mainly due to the outer hole.

I am estimating the amount of windage based on images I've seen and physical copies I have felt. The material thickness almost always comes into play, and then of course the shape.

The worst windage is going to come from most of the units on the outer diameter where they are necessarily not smooth and moving the fastest. The Slon units and ones like it really suffer here. They are little fan blades sticking out into the wind. The Evolve units are almost smooth here, so only suffer a tiny bit. The Mporium units are smooth here, so really suffer no windage from this area.

Then I look at the transition where the material transitions from the outer diameter to the flat face. This is where the next most intense windage is going to come from. If there are protrusions or a hole there then there will be some additional windage. The stock units have one hole here on the outer corner, and thus have a little bit of windage.

Next importantly I look at the face itself and if it has windows taken out to create spokes like a wheel and assume there will be a good bit there, especially if the material is thick. The Slon units again are really bad here.

Finally I look at the center and if it is open to allow for a tiny bit more windage, or completely closed. This is the least important place, but still pays a factor.

I certainly have not performed tests or anything to make these determinations, but I am confident in my ability to make these educated guesses. Take that for what you will.

(I have added most of the above to the thread to help explain things further, and made it clearer that I rate the stock units as "Low" windage.)

Like little fan blades sticking out? Err, no sorry but that is a significant exaggeration. For starters the 'blades' are flat to the hub (assuming they're still fitted properly), they're not sticking out. But I assume you're referring to thickness of the metal fingers 'sticking out'?
But they (the Slon ones) are how thick? About 1.5mm, maybe near 2mm? (going from memory!). Even at 2mm that really isn't sticking out much, I'm not saying it won't have any windage affect at all, but the effect will be very small, certainly compared to the crankshaft etc spinning through the air in the sump where the baulk of the windage losses will be.
The windage losses from VANOS covers with voids will be insignificant compared to the crank. I doubt you'd even be able to measure the differences on a rolling road dyno. Unless you have data to say otherwise?

From your thread at SR20:-
2) It adds to the turbulence inside the engine, which amplifies the dense oil cloud that exists inside the crank case, which promotes oil frothing and hinders oil collection, and in turn promotes more windage losses by other moving components.

Sorry but that is blatantly just incorrect, the air turbulence difference between the different covers is going to be very small, so it's going to make no significant difference to the oil mist in the engine (especially compared to the churning in the sump), and it's certainly going to make no real difference to oil frothing as the vast baulk of that occurs in the sump too (and some in the top of the head). Most of the timing chain and VANOS gears don't sit in or near a large reservoir of oil.
Why did you think that the more open design of VANOS covers would create significant turbulence?

[BenFenner]

Yes, I am talking about the ~2mm of material thickness presented to the dense oil cloud present everywhere inside the crank case.

For sure it is a small factor, but nearly eveything about these covers is a small factor. I personally find it the most important of the many small factors, and I explained why. I see that you disagree. Cool, cool. Please feel free to ignore that column in my chart (or publish your own).

Originally Posted by Assimilator1

the churning in the sump

no real difference to oil frothing as the vast baulk of that occurs in the sump

Most of the timing chain and VANOS gears don't sit in or near a large reservoir of oil

No appreciable churning of oil, airation of oil, or frothing of oil happens in the sump. The proxomity of the sump and the oil within to the sources of windage is immaterial. The crankshaft could be in the head and it would still experience nearly the same windage losses, and feeback loop of turbulance just the same. I'm not sure you understand how this oil cloud forms.

[Chrisyphus]

Okay, so... the original thread made me curious, and a few people have asked for my input. So it did the thing- some research. Step one was getting some vanos hubs on my desk and asking Peter to forgive me for disassembling them lol.

I didn't take any pictures (I will tomorrow), but my God, what a marvel of engineering. There are two moving components to each VANOS gear- the solenoid and the VANOS rotor.

B e a u t i f u l .

Also, the components' manufacturing quality is obscene. The rotors and casings can be wrung together like gauge blocks. I cannot remember a time when I found mass-manufactured parts this nice.

So, without question, I am sure that the openings on the OE VANOS covers are only there for QC in manufacturing. The rotors and retainer plates are identical across all four VANOS hubs. The only physical differences are the sprung gear on the exhaust hub and the sprocket on the intake. It would be VERY easy for whoever was assembling the hubs to get a spring backwards, so it makes sense that they would include a window for the final installer to identify the direction the springs are oriented easily.

I say this because under normal operating conditions, there should be virtually zero oil drainage from the VANOS system from the front of the gear. It is a sealed system (via extremely high surface tolerances), and when the system is set to a specific advance or retard, the solenoids are closed. If there were so much drainage that the cover needed to be designed to accommodate it, that [closed = locked] would not function, and the springs would quickly force the rotor to move erroneously.

Although it seems like what is being said here is that you believe the spring and cover work together to form a centrifugal fan? I can see that, but it would be a wildly inefficient fan- on both gears the wind of the spring opens in the direction it spins, meaning that while the centrifugal force of the air inside the cover would want to go outward, the acceleration of the air in the system would be pushed inward via the direction of the spring which would act as a vane. Having said that, I am guessing there. I have said it a million times since I first heard it from a professor: "The more confident someone sounds while talking about fluid dynamics without having done a simulation or real-world study of the exact situation being discussed, the less you should trust what they say." So, since I haven't done any studies on the topic, I'll end my speculation there lol.

I guess in this thread, it is important to note that Ben has acknowledged multiple times that he is aware he is nitpicking the topic, and I have to keep that grain of salt in mind about the comments. Sure- in the grand scheme of things, the windage being created by the vanos covers is essentially zero compared to the windage coming off the crankshaft and the oil it is slinging everywhere, the piston squirters spraying a stream of oil onto the bottom of a piston moving towards it at mach jesus, the camshafts slinging excess oil in all directions, the timing chains slinging oil off of itself as it changes direction, etc.

But if we isolate the VANOS covers, which are what we're discussing here, yeah, all of these aftermarket designs are going to be worse. I very much doubt that in the grand scheme of things, they add up to a percent difference in windage drag and generation, but relative to OEM, probably several percent.

With that grain of salt in mind, my only beef with the list is the balance category, as I do not know how you did that one. Did you or someone you know actually measure the rotational balance of each brand? Because if not, that category is pure misinformation. I know for a fact that Abdul has his SS covers balanced after manufacturing. I could see where material was removed to put it into balance, and yet on the table, it seems like the only thing that determines whether or not they are "stock balance" is how they look, which is just... not very rigorous. Even if the metal versions have the exact same weight distribution as the stock plastic piece, they are going to weigh significantly more, throwing off the balance of the entire system, which is inherently not balanceable, because its internal and external geometries vary.

I stand behind what I previously said about the purpose of the size and locations of the holes on the OE covers, as well as the supremacy of polyamides in this application (clip-on), over metal, but without question, the best design (and I hate to say this) is CarBahn. It is better than OEM, even if OEM had used a better polyamide like PA46. The reason BMW didn't? For them, making ~100,000+ of these covers, the injection-molded plastic part was probably cheaper. Additionally, it is one less thing for the engine assembly plant to worry about installing- why not let the far cheaper labor at the factory supplying the VANOS gears apply the plastic cover instead of asking one of our assembly line workers to fumble with an oversized washer during timing chain installation?

Originally Posted by a5m

You're right, Evolve uses the same material, that's why it stuck out to me when they said they use 6082. Hoping the engineers here give some insight into that particular alloy's characteristics. I wonder if the deformation concerns mentioned by Chrisyphus still hold.

When a billet plate is made, internal stresses are formed. When you remove most of it from one side, it cups, just like wood, although not as badly. These VANOS covers are made from a billet that is juuuust big enough to fit the part inside of it. This means that as the part is being machined, it will curl inwards. Then, once it is completed, its internal stresses will begin to normalize over weeks to months, allowing it to reopen. Then, when you put it into your engine, it will heat up and likely expand even more, creating an even worse fit. None of the vendors offering Aluminum options has mentioned this at all. This makes me suspicious of whether they understand the issue in the first place, if you're lucky, their machinists are making sure the parts fit the tolerances stipulated in the engineering drawing, and are aware/care that the metal will move around with time and heat. If the machinists care, they will hopefully account for this. It seems to me like all of these products are made to fit a price point. In my experience so far, 95% of these companies that are so, so, so trusted are just... salesmen. If it weren't for the fact that I personally know Abdul and the processes they used to make their covers, I would not have dreamt of installing a clip on a metal cover. Zero chance.

To answer your question about our opinion, A5M: all of our S65 builds get steel bolt-in covers. Nothing else is tolerable on a brand-new $20,000+ engine build.

[BenFenner]

Originally Posted by Chrisyphus

but without question, the best design (and I hate to say this) is CarBahn.

I agree, and am happy to say it.

Originally Posted by Chrisyphus

Although it seems like what is being said here is that you believe the spring and cover work together to form a centrifugal fan? I can see that, but it would be a wildly inefficient fan- on both gears the wind of the spring opens in the direction it spins, meaning that while the centrifugal force of the air inside the cover would want to go outward, the acceleration of the air in the system would be pushed inward via the direction of the spring which would act as a vane.

This is very useful information for me/us. Combined with the QC sight-hole theory, I would take this a step further then and confidently conclude that air/oil flow and spring lubrication/cooling is not part of the design and fully sealing off the spring is of no concern (preferable even).

The "oil behavior" category needs work (or removal). Give me a few days...

Originally Posted by Chrisyphus

my only beef with the list is the balance category, as I do not know how you did that one. Did you or someone you know actually measure the rotational balance of each brand? Because if not, that category is pure misinformation.

The "balance" category is based purely on visuals/images, and with the idea that the stock units are (purposefully?) off balance in dynamic rotation. It is another theory to explain that hole on the stock units. The idea is that the off-axis spring retaining pins throw off the balance of the hub, so a tiny bit of that is compensated for by the hole in the plastic cover in that exact same spot.

So you have units that do have one off-axis hole, or otherwise curiously missing mass in one spot off-axis that is recommended to be placed at the spring retaining pin location. Like the Slon units, or the Ventrax units. I've assumed the rest of the unit is uniform/homogeneous and not specifically balanced. So those got a "stock" rating. "Stock" in this case means unbalanced.

Then some others are completely uniform like the Evolve or MMX units, or are specifically mentioned as "balanced" like the EAE units. Those would get a "non-stock" balance rating or similar. "Non-stock" in this case effectively means balanced.

I hope that makes a little sense...


But now that we've kind of figured out what that hole is actually for*, it's likely I remove the "balance" category. Or change it to describe if a unit is actually balanced or not. Give me a few days...





*It was always a bit of a stretch to think that a tiny bit of missing plastic would make up for the extra mass of two steel pins anyway...







Edit:

Originally Posted by BenFenner

Give me a few days...

I have now updated the original post to reflect the new takes on oil behavior and balance.
The "Oil behavior" and "Balance" columns of the table have been removed. The note on oil behavior has been removed. The note on balance has been completely overhauled.
Before removal, I made a new post in that thread to archive the old stuff for historic purposes.

[Chrisyphus]

Originally Posted by BenFenner

Then some others are completely uniform like the Evolve or MMX units, or are specifically mentioned as "balanced" like the EAE units. Those would get a "non-stock" balance rating or similar. "Non-stock" in this case essentially means balanced.

I hope that makes a little sense...

That does make sense Ben. Thanks for taking the time to explain the thought process!

[Assimilator1]

Originally Posted by BenFenner

Yes, I am talking about the ~2mm of material thickness presented to the dense oil cloud present everywhere inside the crank case.

For sure it is a small factor, but nearly everything about these covers is a small factor. I personally find it the most important of the many small factors, and I explained why. I see that you disagree. Cool, cool. Please feel free to ignore that column in my chart (or publish your own).

No appreciable churning of oil, airation of oil, or frothing of oil happens in the sump. The proxomity of the sump and the oil within to the sources of windage is immaterial. The crankshaft could be in the head and it would still experience nearly the same windage losses, and feedback loop of turbulance just the same. I'm not sure you understand how this oil cloud forms.

Re your 1st point, ok fair enough, but you do make it sound like it's a major factor.
Re your 2nd point, their most certainly is churning of oil in the sump, at the very least the oil being slopped around due to cornering and braking. Even if the crank doesn't touch the oil when the car's stationary, it will somewhat at least when the car's moving. And yes aeration and frothing of oil certainly can happen in the sump! e.g from the crank timing gear for one (And I'm not talking about edge cases either).

Windage loss is another matter, I see I was somewhat ambiguous about that, my bad (I didn't separate air drag losses from oil drag losses). What I meant was the tiny amount of air turbulence from the VANOS covers and hence the air drag (windage losses) is going to be insignificant compared to the windage losses the crank etc experiences (and I did already mention some occurs in the head, I suppose I should've mentioned the timing case too).

[a5m]

Originally Posted by Chrisyphus

Okay, so... the original thread made me curious, and a few people have asked for my input. So it did the thing- some research. Step one was getting some vanos hubs on my desk and asking Peter to forgive me for disassembling them lol.

I didn't take any pictures (I will tomorrow), but my God, what a marvel of engineering. There are two moving components to each VANOS gear- the solenoid and the VANOS rotor.

B e a u t i f u l .

Also, the components' manufacturing quality is obscene. The rotors and casings can be wrung together like gauge blocks. I cannot remember a time when I found mass-manufactured parts this nice.

So, without question, I am sure that the openings on the OE VANOS covers are only there for QC in manufacturing. The rotors and retainer plates are identical across all four VANOS hubs. The only physical differences are the sprung gear on the exhaust hub and the sprocket on the intake. It would be VERY easy for whoever was assembling the hubs to get a spring backwards, so it makes sense that they would include a window for the final installer to identify the direction the springs are oriented easily.

I say this because under normal operating conditions, there should be virtually zero oil drainage from the VANOS system from the front of the gear. It is a sealed system (via extremely high surface tolerances), and when the system is set to a specific advance or retard, the solenoids are closed. If there were so much drainage that the cover needed to be designed to accommodate it, that [closed = locked] would not function, and the springs would quickly force the rotor to move erroneously.

Although it seems like what is being said here is that you believe the spring and cover work together to form a centrifugal fan? I can see that, but it would be a wildly inefficient fan- on both gears the wind of the spring opens in the direction it spins, meaning that while the centrifugal force of the air inside the cover would want to go outward, the acceleration of the air in the system would be pushed inward via the direction of the spring which would act as a vane. Having said that, I am guessing there. I have said it a million times since I first heard it from a professor: "The more confident someone sounds while talking about fluid dynamics without having done a simulation or real-world study of the exact situation being discussed, the less you should trust what they say." So, since I haven't done any studies on the topic, I'll end my speculation there lol.

I guess in this thread, it is important to note that Ben has acknowledged multiple times that he is aware he is nitpicking the topic, and I have to keep that grain of salt in mind about the comments. Sure- in the grand scheme of things, the windage being created by the vanos covers is essentially zero compared to the windage coming off the crankshaft and the oil it is slinging everywhere, the piston squirters spraying a stream of oil onto the bottom of a piston moving towards it at mach jesus, the camshafts slinging excess oil in all directions, the timing chains slinging oil off of itself as it changes direction, etc.

But if we isolate the VANOS covers, which are what we're discussing here, yeah, all of these aftermarket designs are going to be worse. I very much doubt that in the grand scheme of things, they add up to a percent difference in windage drag and generation, but relative to OEM, probably several percent.

With that grain of salt in mind, my only beef with the list is the balance category, as I do not know how you did that one. Did you or someone you know actually measure the rotational balance of each brand? Because if not, that category is pure misinformation. I know for a fact that Abdul has his SS covers balanced after manufacturing. I could see where material was removed to put it into balance, and yet on the table, it seems like the only thing that determines whether or not they are "stock balance" is how they look, which is just... not very rigorous. Even if the metal versions have the exact same weight distribution as the stock plastic piece, they are going to weigh significantly more, throwing off the balance of the entire system, which is inherently not balanceable, because its internal and external geometries vary.

I stand behind what I previously said about the purpose of the size and locations of the holes on the OE covers, as well as the supremacy of polyamides in this application (clip-on), over metal, but without question, the best design (and I hate to say this) is CarBahn. It is better than OEM, even if OEM had used a better polyamide like PA46. The reason BMW didn't? For them, making ~100,000+ of these covers, the injection-molded plastic part was probably cheaper. Additionally, it is one less thing for the engine assembly plant to worry about installing- why not let the far cheaper labor at the factory supplying the VANOS gears apply the plastic cover instead of asking one of our assembly line workers to fumble with an oversized washer during timing chain installation?



When a billet plate is made, internal stresses are formed. When you remove most of it from one side, it cups, just like wood, although not as badly. These VANOS covers are made from a billet that is juuuust big enough to fit the part inside of it. This means that as the part is being machined, it will curl inwards. Then, once it is completed, its internal stresses will begin to normalize over weeks to months, allowing it to reopen. Then, when you put it into your engine, it will heat up and likely expand even more, creating an even worse fit. None of the vendors offering Aluminum options has mentioned this at all. This makes me suspicious of whether they understand the issue in the first place, if you're lucky, their machinists are making sure the parts fit the tolerances stipulated in the engineering drawing, and are aware/care that the metal will move around with time and heat. If the machinists care, they will hopefully account for this. It seems to me like all of these products are made to fit a price point. In my experience so far, 95% of these companies that are so, so, so trusted are just... salesmen. If it weren't for the fact that I personally know Abdul and the processes they used to make their covers, I would not have dreamt of installing a clip on a metal cover. Zero chance.

To answer your question about our opinion, A5M: all of our S65 builds get steel bolt-in covers. Nothing else is tolerable on a brand-new $20,000+ engine build.

Ha, such an engineer. Bought Vanos Units to study. Legend.

Many thanks for your valuable insights Chris. I'm just trying to understand the part about the machinist accounting for the movement of the aluminum with time and heat. How would they account for that? Seems that would not be consistent and vary from one machined part to the next?

I'll pose this question to Ventrax, who's clip on covers I purchased, and will see what they come back with. In the meantime, I had asked about fitment and choice of material, and this is what the designer of the covers had to say:


Firstly, we selected 6082-T6 aluminium for our Vanos covers because it provides an excellent balance of strength, stability, and machinability for this application. While we appreciate and love the properties of 316 stainless steel, we felt it is unnecessarily heavy for a valvetrain component, increases thermal retention, is more difficult to machine, and adds mass where a reduced inertial load is beneficial. Compared with other aluminium alloys—particularly 7075-T6, which we use for high-stress suspension components due to its extremely high tensile strength—6082-T6 is less brittle, more forgiving in thin, clipped geometries, and less prone to stress-corrosion cracking.



Although 7075-T6 is stronger in theory, its brittleness and lower fatigue tolerance make it less suitable for small, precision-machined parts. In contrast, 6082-T6 combines high tensile and yield strength, excellent fatigue resistance, and outstanding dimensional stability, ensuring the clip interface maintains its shape without deforming. Once hard-anodised it creates a ceramic-like surface, so the surface hardness of 6082-T6 increases dramatically—interestingly, above that of stainless steel 316 (while retaining the lightweight, thermally efficient characteristics that make aluminium ideal for this environment).





After reading through the forum thread, interestingly the first photo showing the failed raw-aluminium Vanos covers is exactly the same failure mode we experienced with this particular brand. In fact, that issue is what pushed us to design and produce our own covers.



We still have this failed set we removed from a close friend’s car, and they demonstrate the core problem clearly: the alloy used is far too soft. You can bend these covers with two fingers. With material that weak, the part cannot maintain its geometry under even normal installation force. On top of that, the manufacturer appears to have machined away too much material in critical areas, especially around the clip feature. Because the alloy is so soft, the clip rounds off during installation, and the lack of stiffness allows the entire cover to deform, leading to failure.



Although we don’t have formal lab data from the failed units, we can share our own development evidence:

• Our first set of Ventrax Vanos covers was installed around 3 years ago on a clubsport track car with a highly capable driver.
• We spent 8–12 months testing both on the road and track before releasing the product.
• During this period, the covers were inspected regularly. You can see the cover through the oil-fill hole when trackside, and we also removed the rocker covers multiple times for closer checks.
• None of the covers showed signs of loosening or wear.
• The car receives frequent oil changes as part of normal maintenance, and we never saw a trace of metallic contamination in the oil.
• We can also proudly say, we have never had even one of our Vanos covers fail.

OEM Fitment Problems

We also found that the stock plastic Vanos covers do not fit the Vanos unit particularly well (this is true on the S55 too). Once clipped onto the unit, the OE cover can be rotated clockwise and anticlockwise far more than should be acceptable. The main cause is the sloppy tolerance of the locational key built into the plastic cover—it does not properly fill the Vanos housing slot.



How We Addressed This

We corrected this by tightening the key/slot fit dramatically. Once our cover is fitted, it has no rotational movement. Because the part cannot move, it cannot wear. Combined with stronger alloy selection, increased local section thickness, and hard anodising, the retention clip in our design maintains its shape even after repeated installation cycles.



Whilst we are discussing the design, we also take pride in retaining OEM features wherever possible, even if it adds complexity or cost to the manufacturing process. For the S65 Vanos cover, you will notice we kept the slotted hole on the face of the cover. This aligns with the opening for the clock spring at the end of the Vanos unit. We believe the slot allows oil to flow in and out of this area. While this hasn’t been formally tested, we felt that removing the hole could potentially allow oil pressure to build up, which might directly affect the spring tension and, indirectly, the Vanos unit and cam timing. Additionally, we have maintained the cover’s shape almost identical to the original, except for the slots designed to allow a small amount of flex so the cover can clip on correctly.



We noticed recently that some other manufacturers have removed some of the material around the outer surface of the cover. We believe this is primarily to make the part easier to machine. This area corresponds to the internal stops that define the cover’s depth and position on the Vanos unit, while we don’t believe removing it would cause any functional issues, we just prefer to maintain an OEM+ aesthetic wherever possible.



I also have an S55 Vanos assembly on hand and can share a video demonstrating just how much rotational play the OE covers have—it’s quite eye-opening and, frankly, a bit shocking given BMW’s usual tolerances.

[Assimilator1]

Cool that they responded to you in such detail!
What brand were these 'other' covers they referred to?

[a5m]

Originally Posted by Assimilator1

Cool that they responded to you in such detail!
What brand were these 'other' covers they referred to?

I know! I thought they'd get annoyed and shut down but nope, went into full detail.

My assumption is Slon, since that's what basically kicked the Vanos Cover discussion off.