What alternator amperage should I use?

Delco 12SI. They work awesome...at minumum they are 78 amps, and they charge very well at idle. Very cheap. You can get chrome or powdercoated cases anywhere. Even better is they have an internal regulator, and anyone can take it apart. I switched from a reman 78 amp mopar alternator to the one seen here (78 amp 12SI for a 1985 305 Firebird) for $75 total, and my lights no longer dim at idle, volt gauge never moves. I even used the same v-belt.

There is something about seeing a GM alternator on a Mopar that makes me want to They do work though. I got a 120 amp Denso on my car and it works well. I have an electric fan and electric water and fuel pump. Holds a charge just fine. A mopar 78 amp just wouldn't keep up. I would go for a 120 amp+ alt in your application too. More charging capacity is way better than not enough.

Thanks for the info. Do you have a year or part number from the alternator your using? Does it have a built in regulator? What wiring did you have to change?

Another option is the MOPAR "high amp" option from the mid-late 70's 100+ amps, excellent idle output, heavy. If you have AC, options are limited since the brackets have fixed swing and extra bracing. The "big MOPAR" is a good option with AC... Denso is better without.

I use a GM CS120 alt. They come in 120 and 140 amp versions. There easy to mount to the factory brackets. One off a buick grand national 1986 or 1987 will work. They also can put out alot of amps at idle from what i have been told.

I use a 120A alternator from a 2000 Audi A4. idle output is 70A which is sufficient for 99% of all cars.

Installation is pretty easy but you need a different swing arm (made my own) and some other small thing (longer bolt, wire a diode or charging lamp into one wire etc.). It is internally regulated too!

If you don't "update" the rest of your electrical system using the basic principles discussed on Mad Electrics website, you are risking some serious problems by running a higher output alternator with all your additional electrical load.

I ended up using an upgraded (rewound w/ heavy duty bridge rectifier & regulator) AC Delco CS 144. The comes in Escalades and some full-sized pick-ups etc. It essencially bolts right in with a simple adaptor. It puts out 115+ amps at idle & over 200 amps above a fast idle.

However, the more difficult & time consuming part of the complete electrical system upgrade job, is to wire the car to be able to safely distribute and protect the wiring system.