2500 underdrive pulley

How do you improve the performance of your beastie?
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Rod 2500S
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2500 underdrive pulley

#1 Post by Rod 2500S » Sat Feb 01, 2020 1:37 am

Gday all
Whilst servicing my alternator I reflected on how fast it was going at cruising revs (3500 in top Borg Warner 65).
Hmmm, engine pulley circumference 455mm, alternator pulley 207mm, doing the sums gives us 7693RPM@3500.
Since most of my driving is done at this speed I reasoned that the alternator was going way too quick.
Solution, fabricate an underdrive pulley, in this case from scrap 12mm aluminium.
See pics, it's made in two halves and bolted together with cap screws. If youve got a spare piece of, say 25mm, one piece is the go. But the cap screws do look nice.
Diameter is 90mm, Circumference is 283mm, doing the sums gives us 5627RPM, much better.
It still charges nicely at 800RPM idle speed, result.
Cheers all
Rod
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underdrive pulley 1.JPG

Rod 2500S
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Posts: 40
Joined: Thu Jan 25, 2018 11:26 pm
Location: melbourne australia

Re: 2500 underdrive pulley

#2 Post by Rod 2500S » Sat Feb 01, 2020 1:44 am

and the second pic for some reason failed to attach first time around
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underdrive pulley 2.JPG

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