Alternator issues

So I went out and did some measuring. Crank pulley 5.75" alt 2.5". So if I did it right the alternator shaft is turning 15,400 rpm's, and will have to spin even faster when I take it to the track. At the strip I estimate turning anywhere from 6200 to maybe no more than 6800. I talked to the manufacturer. The gentleman I spoke with didn't really know much about their alternator's. All he could tell me that it was good up to 8000 rpm. But couldn't say if that was engine rpm oralt shaft rpm. Not sure how it can be a drag race alt and only be able to handle 8000 rpm at the alt shaft. Alternator's are a baffling part.