Bill,

Here are couple of marginally smaller diameter single groove pulleys that indicate will fit a 10si unit. None of these are mine, just stuff I found perusing the web.

These were picked based on an assumption that you are using the 5/8" wide belt.

https://store.alternatorparts.com/2...tural-industrial-marine-alternators.aspx

https://store.alternatorparts.com/a203-extra-wide-belt-pulley.aspx

Haven't tried to do the math to figure out if the reduction in pulley diameter is enough to raise the RPM level to a more acceptable level or not???

Perhaps the minor reduction, coupled with a little deeper set of the belt in the groove is enough???

Would be interested to know if someone wants to do the math.

Dan

~ Dan
1951 Chevy 3 window 3100
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