I know a HO alt has more amps, does the idle output increase as well?
yes, usually, but might want to check the specs of the alt your looking at to make sure. I've noticed some HO alts don't really put out much more at idle then a factory alt.
another option would be to try to find a smaller diameter pulley for your alternator, this will spin the alt a little faster at idle. although im not sure of the consequences this might have at higher rpms. I have a feeling this is how many of the ho alt makers increase output of their lower output alts.
here is a quote from alternatorparts.com
"The Question has been asked:
How do I get more power at Idle?
Improving Alternator Output at Idle Speed
There are several ways to get more power at lower engine speeds. If you only require a little more power at lower engine speeds you may be able to use a smaller pulley. The smaller pulley turns the alternator faster at lower speeds thus making more power. When using a smaller pulley care should be taken not to over rev the motor. If you over rev the alternator with a smaller pulley the alternator can fail. I have seen internal and external fans explode and go through the hood of the vehicle with a $10,000 custom paint job.
The best way by far to obtain more power at lower engine speeds is to install an oversize alternator. The physically larger alternators produce more power at lower engine speeds and are much more reliable at higher outputs. Installing a higher output alternator that is the same size as your original alternator will not give you more power at idle unless they use a special rotor stator combination."
You should be able to get away with it if you stay 1000-2000 rpms below engine redline like most people usually do.
