Without an answer to "why", but interesting non the less, here are the drive
ratios for various accessories on the O-540 and IO-540 Lycomings per the
Lycoming OP Man.

Starter 16.556:1 CCW
Alternator 3.2:1 CW
Vacuum Pump 1.3:1 CC
Hyd Pump 1.385:1 CW
Tach 0.5:1 CW
Prop Gov 0.895:1 CW
Mag Drive 1.5:1 CW
Fuel Pump 1:1 CCW

Jim

These ratios may be different for dual magneto drives or wide cylinder
flange engines.


"Dave Butler" wrote in message
news:1145999840.940424@sj-nntpcache-3...
Jim Burns wrote:
Different gear ratio.... Lycoming 6 cylinders typicaly run a ratio of
1.3 :
1, so 700 hours is the most you should expect. Pretty good article on
the
sacramento sky ranch site.

Thanks, Jim. I didn't find the article on the SSR site, but I believe you.
Do
you know what the rationale is for making the accessory shaft spin faster
on 6s?

Dave