My understanding is that the deep-groove pulleys were used on engines that would see regular high r.p.m. use. The grooves were deeper to prevent the belts from jumping off the pulley. From an engineering point of view I don't think the diameter of the pulleys (over-drive or under-drive) was important to a mass production car manufacturer, and they tended to stay the same diameter as production pulleys.
The engineers didn't worry about over-speeding the alternator or other driven accessories EXCEPT for the a/c compressor. They kept a/c off the option list for the radical engines, and for cars like the '67 Chevelle SS396 with air conditioning they only came with 3.07 axle ratios regardless of transmission or engine horsepower, in order to prevent compressor damage from over-speed.
It was a big thing back in the 80s/90s to install underdrive pulleys for Mustang 5.0 in order to reduce the parasitic losses. You just have to watch out for an undercharged battery if you don't keep the revs up.
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67 Chevelle Malibu Sport Coupe, Oshawa-built 250 PG never disturbed.
In garage, 296 cid inline six & TH350...
Cam, Toronto.
I don't judge a man by how far he's fallen, but by how far back he bounces - Patton
High horse 409s, and maybe late 348s, solid lifter engines, had deep groove pullies and were not available with AC. I always wondered why.
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic
