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Old 12-14-2020, 09:43 PM   #9 (permalink)
Ecky
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ND Miata - '15 Mazda MX-5 Special Package
90 day: 39.72 mpg (US)

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Quote:
Originally Posted by serialk11r View Post
Shutters on a fan aren't great because the pressure drop at the inlet consumes some of the power you just saved. My preferred method for alternator cooling would be an undersized fan (half the flow) with a supplemental electric fan for low speed.

Fans and coolant pumps consume power proportional to the cube of rpm, so those are the biggest gains, and they're big enough to be noticeable even for street driving. Power steering is inefficient because steering assist is not needed most of the time, but the flow control valve built in means parasitic losses are almost linear, proportional to rpm.

My thinking around accessories is underdrive them a bit, and don't think too much about it, with the exception of the cooling system. On a race car that's always running at high speed, you can underdrive everything more and avoid prolonged idling. For a street car that's usually running at low engine speed, the extra hp lost at high rpm isn't usually a concern.
This is getting off in the weeds a bit, but I could use an opinion:

Honda's K20 and K24 motors are nearly identical, and share accessories. The K24 block is around 1cm taller, has a longer stroke, and a slightly bigger crank pulley. The K20 is a square engine with a higher redline, and a smaller crank pulley.

I understand these pullies are dampened, which protects all sorts of bits inside the engine. The smaller motor with the higher rev limit has a comparative "underdrive" pulley for accessories. I wonder if the pulley being larger on the bigger motor is only to spin the accessories faster, or if it also serves to provide more dampening. Do you think changing the crank pulley would be safe?
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