I am thinking of replacing and upgrading the original old alternator on my 94, 3.9 +8. Would like to put in a 120amp alternator does anyone have any recommendations?
Is there need for such a large capacity alternator Bruce? If you have unusually high electrical loads I can maybe understand otherwise not. For example I had two nominal 12 volt alternators on my narrow boat totalling 250 amps but they had to re-charge a total battery capacity of over 900 amp hours (nearly twenty times your battery capacity) most being the service bank in use in the evenings when engine not running and no shore power.
The ideal charge rate in lead acid batteries is C/10 for greatest longevity, where C is the battery capacity in amp hours and charge rate measured in amps. Expediency can justify higher rates up to C/3, being a balance between reasonable longevity and limited re-charge time.
Another example is my 60 year old diesel Land Rover which manages with it's OE 22 amp dynamo, it's 10 year old battery still going strong. I admit this is marginal though and a sop to originality
A modern alternator suitably geared to charge at fast idle close to a max output of 50 amps would be more than adequate surely.
