Alternator Upgrade?
Fleet Owner
Joined: Nov 2003
Posts: 27,890
Likes: 3,607
According to my calculations, the stock pulley is about 68 mm. The 58 mm does it's best work at idle, such as when you first start the truck...you have the glow plugs working and the starter just sucked a bunch of juice out of the batteries. The 58 mm isn’t mandatory, but helps provide extra amps at a critical time. (Idle)
sorry, the pictures are dark.
sorry, the pictures are dark.
Hotshot
Joined: Dec 2014
Posts: 17,825
Likes: 3,108
From: Jersey Shore
I had the Bosch 140a from Amazon on for years and it never let me down. I put one on a truck that has gone over 80k and it has no issues. There are a lot of options.
The only caution about smaller pulleys is over-speeding the alternator at full RPM, but they are usually designed around the higher range of a gas motor. Most stock alternators are run at 2,000rpm around idle.
Along with the pulley diameters comes the driven ratio. So just to document those here is what is called out by Ford for the 2003 model year in the literature I have:
"The standard single generator system consists of a single generator mounted on the top right of the engine (diesel) or top center of the engine (gas). The gas engines use a 6G 110 amp generator with a 2.96:1 pulley ratio. The 6.0L diesel uses a 6G 110 amp unit with a 2:79 pulley ratio, while the 7.3L diesel has a 6G 110 amp unit with a 2.49:1 pulley ratio.
The optional dual generator package (7.3L and 6.0L diesel engines only) consists of an upper/lower dual generator system. The 6.0L upper generator is a VR42 140 amp generator with a 2.79:1 pulley ratio, with the 7.3L upper generator being a 6G 110 amp unit with a 2.49:1 pulley ratio. The 6.0L lower generator is a 4G 120 amp generator with a 3.00:1 pulley ratio, while the 7.3L lower generator is a 6G 110 amp unit with a 2.32:1 pulley ratio. Thus the upper and lower generators are not interchangeable."
The only caution about smaller pulleys is over-speeding the alternator at full RPM, but they are usually designed around the higher range of a gas motor. Most stock alternators are run at 2,000rpm around idle.
Along with the pulley diameters comes the driven ratio. So just to document those here is what is called out by Ford for the 2003 model year in the literature I have:
"The standard single generator system consists of a single generator mounted on the top right of the engine (diesel) or top center of the engine (gas). The gas engines use a 6G 110 amp generator with a 2.96:1 pulley ratio. The 6.0L diesel uses a 6G 110 amp unit with a 2:79 pulley ratio, while the 7.3L diesel has a 6G 110 amp unit with a 2.49:1 pulley ratio.
The optional dual generator package (7.3L and 6.0L diesel engines only) consists of an upper/lower dual generator system. The 6.0L upper generator is a VR42 140 amp generator with a 2.79:1 pulley ratio, with the 7.3L upper generator being a 6G 110 amp unit with a 2.49:1 pulley ratio. The 6.0L lower generator is a 4G 120 amp generator with a 3.00:1 pulley ratio, while the 7.3L lower generator is a 6G 110 amp unit with a 2.32:1 pulley ratio. Thus the upper and lower generators are not interchangeable."
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