Porsches run best at 14.2-14.5+
13.75-14 is ok but not really good enough. your car may seem fine but 100% performance happens when voltage is closer to 14.5
A key ground connection is the one between the regulator panel and ground stud behind filter.

This thread discusses the importance of a good connection and the differences even small resistances make.

Alternator Cable

If you want to check your alt output
remove the rear regulator panel and the small 3 fuse panel. look for the big red wire in the three fuse panel.should be the middle one/ that's coming right off the alternator. also it's east to blip the throttle from there.
at idle perfect would be 14.2,the slightest rev takes it to 14+ ,magic number being 14.56especially for carburated cars.A carbed car will not run right at 13.5-13.75.if you hit 14.5+ your car can handle all the accessories without worry. if you have more than 1 volt diff between the rear panel output and the reading at the battery then you have too much resistance somewhere in the line.
Also .don't just take one reading and do everything based on that.take a few readings over a period of time . You will not get a correct reading with a low battery either. A battery has to be at a certain state before it can even accept a full charge. Best to drive the car with NOTHING on for a while and then test it .do that a few times for the most accurate reading of your alternator.

Where does that magic 14.56 come from and why especially for carbureted cars?

Why not and what does a carb have to do with a battery?

Isn't it 0.5V for a 12V system?

no magic .if everything is bang on the system will show 14.56
amperage. the voltage reading is just an indicator .You need a big spark to blow that dump of fuel properly.
13.5-13.75 ign system is not giving a enough amperage to produce the big spark .most noticeable in carbed cars .you get a bawking feeling when you nail it in say second gear.

the voltage reading if all is up to snuff will be 14.5 something . I just know from years of experiance that if you see 14.56 or above.(if alls fine it will never be much higher than that,maybe a fliker) then that is the best you can get and your car runs excellent. at 14-14.2 it runs fine and I'm sure some will argue there is no difference. I'm telling you there is .
It's got to do with the amperage being drawn in the system as the revs increase and the minimum amperage needed to give you the big spark you need.

your right on the .5. I just rounded off to 1 because if there is an issue it is usually closer to a 1 volt difference

I got a cigarette lighter voltmeter from Amazon. Works great and has been a big help in tracking down intermittent alternator problems. Amazon.com: Vector VEC008 Digital LCD Voltmeter, 12 Volt: Automotive

^^^ I think you may have had a weak component somewhere if you needed that voltage to get a good spark.

Regulators regulate at 14.4V for FLA batteries which is what early cars came with and most of the time, the voltage is lower while driving.

I use my radar detector voltameter function , monitored at cig/lighter. This measurement point has been (and continues to be) checked every so often against (compared to) battery terminals to ensure I account for this slight voltage drop. Hope to get a nice analog meter in there soon!!! This setup audibly alerted me to a +16.5 VDC spike...happened once that day,..the next day: again. Installed new alternator and regulator (found the original 1989 factory hardware in there!!!!!!!!!!

BEST!

Doyle

What...WHAT..??

Alternators DO NOT fail as a result of having to supply their maximum rated output current, and alternator internal design aspects do not allow them to exceed that maximum design rating. Excessive voltage output, >16V, but below the maximum output current rating, yes, but only with a failed/failing regulator "commanding" same.

Wow, I feel as if my leg is getting longer and longer.

Battery terminal/(post) voltage with the engine running, charging system operating properly, and low electrical loading is strictly a function of battery SOC. And.... Battery terminal voltage at a specific SOC level, say 70%, will be different in wintertime vs summer.

Automotive charging system regulators use a PWM, Pulse-Width-Modulation, voltage dutycycle to regulate to get an average output voltage. Your voltmeter might read an average of 14.5 when the actual peak voltage is somewhere NORTH of 16 volts.

I once had a shorted phase, one of three, in an alternator and things seemed to work perfectly find except the system voltage ripple content was over 4 volts. I have no idea how long the car had been running that way, I only noticed it when I discovered the alternator case was running extemely HOT.

I cut the stator winding to that one phase as a temporary fix and as far as I know the car went to the "graveyard" that way.