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?
Quote:
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.
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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.