By Carl Heideman
https://classicmotorsports.com/articles/power-conversions-upgrading-modern-alternator/
Note that with high capacity fuel pumps, radiator fans, upgraded headlights, stereo, and other electrical equipment even the 55 amp alternator may be a bit marginal.
Jim
Yeah I would agree with what Jim said. If your running a carb, sometimes you can get away with a lower amperage unit.
With EFI and electric cooling fan(s), it's best to have at least 80 amps or more. Most newer vehicles are running 120 to 150 amp alternators due to all of the electronics.
Currently I'm running a 150 amp unit, mainly for the increased amperage output at idle. EFI and controllers like a stable voltage source, so by having "more then you need" amperage wise, it allows the fueling to be more consistent at lower RPM. The added bonus is that your cooling fan will run at it's maximum rated capacity as well!
Bill
I chuckled at the term "modern". Those little Nippondenso alternators are great... but mine is over 30 years old already!
Bear in mind also, not all 80 amp alternators are equal. It does little good to install a 150 amp alternator that puts out 30 amps at idle. Granted that's an extreme example but not as far off the mark as you might think. A good example is the old venerable Delcotron. Originally a 63 amp unit, by changing the field winding they can go up to 100 or maybe even 120 amps. But to do that they lose capacity at slow speed, so in the end the 63 amp unit actually charges better around town.
Jim