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Thread: M60 dudebros: Underdrive pulleys (VAC discontinued)

  1. #26
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    Quote Originally Posted by flying525 View Post
    Just like he buys the aluminum grade he needs based on its published characteristics for that grade. There must be similarly published characteristics for different types of plastic blocks.
    That's more or less true, but there are some major problems.
    1) The plastic in things like a BMW pulley is proprietary. You can't know what it is, and you couldn't buy it if you did know.
    2) A block is the native and cheap form for aluminum to be in. Tiny pellets for injection molding is the native and cheap form for plastic to be in. Plastic blocks are EXPENSIVE. Even the most useless nylon would be double the cost of aluminum, and something that could touch the properties of BMW proprietary plastics could literally be hundreds of times more expensive. I kid you not, I have machined blocks of plastic that would fit in your hand and cost $5000 (for scientific stuff).
    3) It's extremely unlikely to match the strength to weight ratio of aluminum. BMW doesn't use it for strength, they use it because injection molding on a massive scale is far cheaper than machining. If you want lighter weight (and are willing to pay for it) he could use 7075 or 2024 (etc...) aluminum and make it much thinner than the same part in 6061. It's difficult to know exactly how strong it needs to be though, it's usually just a matter of failing sooner. Ideally you'd like the lifetime of a pulley to be very long, so they're stronger than they need to be. Your money would be 1000x more effective if spent on a lightweight flywheel.

  2. #27
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    ^good points, Layne, very interesting. The plastic/nylon version of this, while cool and objectively higher performing due to weight, would invariably be more expensive according to Greg. And if you think he'd test one factor and leave the rest to chance, you don't know Greg

    These aluminum pulleys will be pretty cost-effective; no one will dispute the advantage of a potentially 4x or 5x lighter pulley, but it seems there is a likely reason I've never seen aftermarket underdrive pulleys in plastic: cost, to get them right.
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  3. #28
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    Layne, thank you for that very clear explanation. It now makes sense. Facts when clearly laid out trump opinion. Appreciated.

    BB, just a note that I got an underdrive pulley for my M50 from ECS tuning (or was it turner?) For my ps pump. It was made of plastic. And my wp pulley is made of plastic but that's from bmw although strangely it cost the same as a new aluminum pulley.

  4. #29
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    Side note: Greg received the pulleys today. Woot!

    Quote Originally Posted by flying525 View Post
    BB, just a note that I got an underdrive pulley for my M50 from ECS tuning (or was it turner?) For my ps pump. It was made of plastic. And my wp pulley is made of plastic but that's from bmw although strangely it cost the same as a new aluminum pulley.
    That makes the first widely-available underdrive pulley I've heard of being made in plastic, but cool! I get that BMW can probably make them in bulk cheaply, but I wonder if race teams without a budget consider going plastic or nylon for pulleys--obviously they might be interested in a much lighter rotating component.
    - Brent
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  5. #30
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    Hey my bad, the plastic wp pulley I got was not an underdrive pulley it was a normally dimensioned one. But the ps one I got was an underdrive pulley. It was priceir than a normal alum pulley but not by a whole lot more. That's why I bought it, my ps pulley was fine. Let me see if the link is still up somewhere.

    Can't find it !

  6. #31
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    Uneducated question: how much benefit would one expect to gain from these pulleys? From the effect of spinning slower, or the weight, or both? What's the drawback?

  7. #32
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    Quote Originally Posted by David9999999 View Post
    Uneducated question: how much benefit would one expect to gain from these pulleys? From the effect of spinning slower, or the weight, or both? What's the drawback?
    VAC claimed a gain of 8.5 horsepower, one draw back to some is spinning the water pump and power steering pump faster than stock.

  8. #33
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    ^Yep. Underdriven pulleys fall into the category of bolt-ons; the more you have, the more you'll notice. Throwing underdrive pulleys on an otherwise stock car will not net a noticeable difference.

    These pulleys are heavier than the plastic they replace, so I assume underdriving the belt is a better HP per $ gain than lighter weight pulleys.
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  9. #34
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    Quote Originally Posted by UnrulyGrace View Post
    VAC claimed a gain of 8.5 horsepower, one draw back to some is spinning the water pump and power steering pump faster than stock.
    Slower than stock, not faster.

    FWIW, there is a factory 'underdrive' pulley for the water pump: the normal euro version. All US cars got the hot climate water pump pulley, the normal one is slightly smaller (and uses a different belt). I can't imagine you would notice the difference though.

  10. #35
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    Quote Originally Posted by Layne View Post
    Slower than stock, not faster.

    FWIW, there is a factory 'underdrive' pulley for the water pump: the normal euro version. All US cars got the hot climate water pump pulley, the normal one is slightly smaller (and uses a different belt). I can't imagine you would notice the difference though.
    Duh, you're absolutely correct.

  11. #36
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    Quote Originally Posted by UnrulyGrace View Post
    VAC claimed a gain of 8.5 horsepower, one draw back to some is spinning the water pump and power steering pump faster than stock.
    An underdrive pulley should cause whatever to spin slower, not faster.

  12. #37
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    Quote Originally Posted by flying525 View Post
    An underdrive pulley should cause whatever to spin slower, not faster.
    Right, I admitted saying the wrong thing in the post above. Obviously, underdriving slows the spin...long day.

  13. #38
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    I like the idea of the M50 style underdrive crank pulley, smaller diameter and reduce rotational weight. However, getting away from the harmonic damper sounds like a bad idea.

  14. #39
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    Prototipos will be printed today for comparison to the VAC units, at which point the VACs will be shipped back to Taylor post-haste.


    THANK YOU, TAYLOR

    Greg plans to mill in a week or two and install the first set on my 540iT for test-fit, and we'll be in bidnuss!

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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  15. #40
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    About the only drawback I've heard for underdrive pulleys on these motors (including the M50-based ones in this), aside from sometimes being overpriced, is that certain cars will not respond as well to having, say, the water pump under-driven. If the car's pump is already partially obstructed/on the way out/etc, spinning it slower could cause cooling issues. Same for the other pulleys like PS.

    Not exactly a drawback of the pulleys themselves, mind you, just a note. Maintenance should always come before modenance.
    - Brent
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  16. #41
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    Can't wait!

  17. #42
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    Quote Originally Posted by Layne View Post
    If you want lighter weight (and are willing to pay for it) he could use 7075 or 2024 (etc...) aluminum
    Oops, I forgot to add that Greg is going for billet 7075. I know he used that stuff for the F50 caliper brackets I have in my garage, they are deceptively light for a metal part...
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  18. #43
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    Tooling for production is on the way to Greg.
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  19. #44
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    For the water pump, there is a non-USA pulley that's 117mm instead of 104mm diameter. It's part number 11511733429. Not sure how big the VAC item is, but if it's similar then this might be a way to save some money on the set.

    For plastics - the OEM pulleys usually show the grade right on them. It's probably glass-filled nylon.

  20. #45
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    M60 dudebros: Underdrive pulleys (VAC discontinued)

    Great point Eddie, I'll double check diameter tonight and update people. Going OEM if possible for the same diameter will more than likely be cheaper and definitely lighter if it's glass reinforced nylon. Guys keep this option in mind, might be a good bang for your buck.

    -Greg


    Sent from my iPhone using Tapatalk

  21. #46
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    will this help m60 e31 840ci??

  22. #47
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    oh hey, i'd be in for a set of these. Have i missed the boat yet?

    i'm much easier to get a hold of on Facebook, instagram, or email. Wes Van Heest online, vanheestvisual on IG, or wes 825 on gmail
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  23. #48
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    Quote Originally Posted by perj42 View Post
    will this help m60 e31 840ci??
    Beneficial for all M60s yes, but do your own research honestly.

    Quote Originally Posted by staystackin View Post
    oh hey, i'd be in for a set of these. Have i missed the boat yet?

    i'm much easier to get a hold of on Facebook, instagram, or email. Wes Van Heest online, vanheestvisual on IG, or wes 825 on gmail
    You're good Wes, production hasn't started yet but tooling is on hand. I'll keep your contact info on hand when it comes to payment.

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    Edit: I may actually be the hold-up here, if Greg is waiting to test fit on my M60. I'll find out, we've both been busy.
    Last edited by BleedsBlue; 07-17-2017 at 06:36 PM.
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  24. #49
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    Is it possible to under drive only what we want? I'd like to buy a full set but I really would rather not underdrive my water pump..

  25. #50
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    Power steering pulley grooving is the last item Greg is finishing for these, but...exciting cost-savings already! See below.

    Quote Originally Posted by Billyj View Post
    Is it possible to under drive only what we want? I'd like to buy a full set but I really would rather not underdrive my water pump..
    Woah, Billy. Prescient much?

    I was just talking to thread and we all owe user @eddycooper a beer or six. The OEM non-US water pump pulley, 11511733429, is so close to the VAC in size (and lighter) that Greg isn't even going to make a water pump underdrive! 11511733429 is $25 from most sources, so again, we really owe @eddycooper at least a premium six pack

    Updated the first page, and here's the post for which we can all thank Eddy:

    Quote Originally Posted by eddycooper View Post
    For the water pump, there is a non-USA pulley that's 117mm instead of 104mm diameter. It's part number 11511733429. Not sure how big the VAC item is, but if it's similar then this might be a way to save some money on the set.
    Last edited by BleedsBlue; 07-20-2017 at 12:41 PM.
    - Brent
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    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

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