Quote:
Originally Posted by churchx
Ouch. Somehow it messed up in my mind and came out opposite. Right, for same belt speed driven accessory pulleys need to be oversized to turn slower. And driving (crank) pulley needs to be undersized to turn all driven pulleys slower at same rpm.
BTW, any nfo, how much each driven accessory uses up power, and which are more & which are less safe to slow down (and within what range)?
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This is from another thread.
“std crank pulley is 143 OD, alt pulley is 57.5 and water pump is 132
alternator is 130Amp @ 14v = 4.4Hp to turn assuming 55% efficent and due to the pulley ratio its running @ 2.5 x crank speed
so adding 10mm ( Fensport pulley) reduces the ratio to 2.12 so 15% slower = 3.75 Hp to turn so + 0.65hp gain
Water pump std ratio is 1.08 with fensport pulley is 0.94 and water pumps typically take 7bhp to turn so again about 15% slower so 6 bhp to turn so 1 bph gain so in total, you should get about 1.6bhp gain”
Now at first I didn’t like the idea of underdriving the water pump but apparently alot of guys on the uk forums have been doing it with no problems and fensport claims it has no negative effect on engine temps. So now I’m thinking of just getting both and using new belt. Can argue the effects of lightweight pulleys. But oversized/underdriven pulleys do give some gains.