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I got a measurement on a spare engine, 109mm exactly. So at the rev limiter of 8200rpm, the water pump will hit 10000rpm! Holy crap.
That means the one aftermarket pulley available must be 116mm, because 7mm off that would be exactly 6% reduction as they claim. I could probably push it to 124mm without clearance issues, but that might be tight, so I'll stick with 121mm, which is 2.5mm greater radius than the Monkeywrench Racing pulley.
At 121mm, my water pump's power consumption will be reduced approximately 27%.
I am thinking of having the ID be 108.9mm, sticking it into hot tap water and heating it to 140F would make it expand to 109mm, and then it would cool for a slightly tighter fit.
I'm debating what material to make this out of. I feel like this isn't actually that important, but the marginal cost of using something better is pretty small. PETG is really cheap and I can find someone in San Francisco to do it for me, nylon and alloy 910 would be more difficult to find, and glass filled nylon would be awesome but quite expensive. I'm also unsure what to secure the plastic ring to the pulley with. I feel like normal superglue should be fine, but the strength is not that great. Two part epoxy seems like it would make a giant mess. Hmm...
Any input?
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