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serialk11r · 08-17-2016, 09:02 PM

Hey everyone,

I'm getting close to closing the deal on a 2ZZ-GE MR2 Spyder and replacing my FR-S, and like any proper car person I'm already thinking about mods.

The 2ZZ-GE is a pretty good engine considering it was designed before the turn of the millennium, and gets pretty good gas mileage. That said, I can't just leave it alone.

The most obvious bolt-on mod for fuel economy is an underdrive water pump pulley. The pulley is driven off the back side (smooth side) of the belt and has no grooves, so that got me thinking...how hard can it be to make/modify a cheaper off the shelf pulley or stock pulley to a larger diameter?

Monkeywrench Racing sells a 6% underdrive pulley, but 0.94^3 = 0.83 is only a 17% power reduction for 70 dollars. How much power that saves is an unknown, although you gain 3hp at 8000rpm supposedly if you use that along with the alternator underdrive pulley (though I imagine a bunch of that is the fact that the alternator rotor is kind of heavy and has significant inertia).

If say the water pump consumes 6hp at 8000rpm, that's something like 230W at 3000rpm (cruising). The underdrive pulley drops that to 190. If I can bump the diameter up to get 12% underdrive, that drops me to 155W (enough savings to power a pair of HID/LED headlights), and gains me 2hp at 8000rpm.

My thinking is that if some plastic can work as a pulley material, I can buy a section of plastic disk or pipe, machine the center out and epoxy it to the stock pulley for the desired diameter increase. Or, 3d print a plastic ring using carbon reinforced plastic and machine it for a smooth finish. The scary bit is that it has to hold up to 8500rpm...thoughts?

08-17-2016, 09:02 PM	#1 (permalink)
serialk11r Master EcoModder Join Date: Jan 2012 Location: United States Posts: 1,756 spyder2 - '00 Toyota MR2 Spyder Thanks: 104 Thanked 407 Times in 312 Posts	DIY underdrive pulley? Hey everyone, I'm getting close to closing the deal on a 2ZZ-GE MR2 Spyder and replacing my FR-S, and like any proper car person I'm already thinking about mods. The 2ZZ-GE is a pretty good engine considering it was designed before the turn of the millennium, and gets pretty good gas mileage. That said, I can't just leave it alone. The most obvious bolt-on mod for fuel economy is an underdrive water pump pulley. The pulley is driven off the back side (smooth side) of the belt and has no grooves, so that got me thinking...how hard can it be to make/modify a cheaper off the shelf pulley or stock pulley to a larger diameter? Monkeywrench Racing sells a 6% underdrive pulley, but 0.94^3 = 0.83 is only a 17% power reduction for 70 dollars. How much power that saves is an unknown, although you gain 3hp at 8000rpm supposedly if you use that along with the alternator underdrive pulley (though I imagine a bunch of that is the fact that the alternator rotor is kind of heavy and has significant inertia). If say the water pump consumes 6hp at 8000rpm, that's something like 230W at 3000rpm (cruising). The underdrive pulley drops that to 190. If I can bump the diameter up to get 12% underdrive, that drops me to 155W (enough savings to power a pair of HID/LED headlights), and gains me 2hp at 8000rpm. My thinking is that if some plastic can work as a pulley material, I can buy a section of plastic disk or pipe, machine the center out and epoxy it to the stock pulley for the desired diameter increase. Or, 3d print a plastic ring using carbon reinforced plastic and machine it for a smooth finish. The scary bit is that it has to hold up to 8500rpm...thoughts?