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Discussion Starter #1
running an Explorer 302 with the Explorer front dress. bought a TuffStuff 225amp alternator 7778F which is for that Explorer. its not charging at idle but just a tab off idle its fine. i need it to charge the most when at idle to power a winch. i asked TuffStuff about running a smaller pulley and they said it would help but they dont make one. they said the shaft is .668 but did not say what size the pulley is. i THINK it is 58mm, but not exactly sure where you measure from to be honest. anyone recommend a place to get a smaller pulley?

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You want to run the typical alternator at a minimum of 2,400 shaft rpm and a max of 18,000 shaft rpm. A 3:1 alternator to crank ratio is a good rule of thumb. Here is an online pulley speed calculator to check out: https://www.blocklayer.com/pulley-belt.aspx

As indy2000 mentioned, ASP ( https://www.autospecialties.com/ford/ ) sells alternator overdrive pullies. I have used their 1 7/8" pulley (ASP520004) with good results. Powermaster ( http://www.powermastermotorsports.com/catalog.html# ) has 1.90, 1.92, and 2.00" pulleys listed on page 88 of their online catalog.

Are you running an underdrive crank pulley? If so, changing back to the factory crank pulley will help too. My factory crank pulley is 5.75" and my underdrive crank was 4.50". Edit: IIRC, the crank underdrive pulley on it's own slows everything down 20-22%.
 

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PA performance alternators has a good selection of overdrive pulleys. The thing I like most is that the ribs are deeper and they grip the belt better than the factory stuff.
However......do your math and make certain you are never going to over spin your alternator when driving.
I bought a pulley from them to get rid of a startup chirp/squeal that I had determined was the alternator pulley. I got an overdrive one because I figured some extra juice at idle and low RPM would not be a bad thing.
I was out "driving spiritedly" not long after, ran the RPM past 6K and fried my alternator and the pigtail that plugs into it. So.....I ordered a factory size pulley, bought a new alternator and pigtail and learned an expensive lesson.
 

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Discussion Starter #5
its whatever size crank the Explorers used, id have to measure it when i get a chance. do you measure the crank and alt pulley by the OD of the outside big rib? or the OD of the inside ribs? cause the outside rib is 2.5" and the inside ribs are 58mm and both those sizes come up when i look them up. but if it is 2.5" then i think a 1-7/8" might be too big of a jump. assuming i have a 6.5" crank my ratio would only be 2.6x. but the 1-7/8 would be a 3.46x ratio. but assuming i never go over 5k RPM which i dont, that would be 17,333 alternator speed
 

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Like said, ASP makes a 1 7/8" pulley and i've used one with U/D pulleys for 20 years without issue. However, if you hope on ebay, there's a wide variety of alt pulley sizes to pick from.
 

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March is another source of alternator pulleys too. Here is some more alternator info from Powermaster. It is interesting they call out 18,000 rpm for Delco style cases and 20,000 rpm for Denso units. PA mentions 16,000 rpm in their info.
 

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If you have not already pulled the trigger on a pulley, I still have the 48 mm pulley I bought from PA Performance.
VERY low miles. PM if interested.
 

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Discussion Starter #10
got a 1-7/8" pulley from a members here. the pulley was offset a couple ribs and the hub was too thick to use the lock washer. so i made the mystake of grinding the hub about 3/16" to get it back in alignment. then realized the reason its offset is because now it rubs the case. used a washer to get it back how it was. seems good, hopefully it wont slip due to the washer and no lock washer. now stays a constant voltage even down to 500rpm. gonna have to buy a bit shorter belt, the tenshioner is well out of range now

the original pulley was 2.5" and the crank pulley was 6" so it was only at a 2.4 ratio. the auto part store alternator pulley i had before was also 2.5" so i guess thats factory size. a 2" pulley would have been the best choice staying 3.0 ratio and i may swap to one in future. but the 3.2 ratio should defiantly give good idle power. but gonig with the safer chocie iof 16,000 RPM max means i shouldnt go over 5000 rpm. so i might go 2"
 
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