knight rider online

I remember reading some of the stunt cars used Pontiac 301s
with race cams, cat converters removed, and glass packs but
can't confirm

I just remember when KITT was approaching a jump or during some interior shots
when the speedometer was climbing past 200 he sounded like a top fuel dragster.
Were these sounds dubbed in for effect or were they actually coming from the car itself.

Junk yard dog episode has a prime example at the test track
when Michael and KITT slide around the corner and approach
a wooden wall before turbo boosting over it

the stunt cars had 350 engines with no smog junk. And most sounds on TV and movies are dubbed in. Even on the Dukes of Hazzard the engine sounds were dubbed in. If you listen on some Dukes eps you will here sounds from the movie Bullitt.

As for here cars they probably had stock 305 engines.