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.
^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.
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.
Side note: Greg received the pulleys today. Woot!
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.
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 !
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?
^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.
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.
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.
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.
Can't wait!
Tooling for production is on the way to Greg.
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.
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
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will this help m60 e31 840ci??
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
Beneficial for all M60s yes, but do your own research honestly.
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.
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..
Power steering pulley grooving is the last item Greg is finishing for these, but...exciting cost-savings already! See below.
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:
Last edited by BleedsBlue; 07-20-2017 at 12:41 PM.
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