Migration using pg_restore

Note:
Assumption tables are already created and/or in existence.

I dump all data from a 7.3.5 db using LATIN9 encoding.
When I restore it back to a 8.1.3 db using LATIN9 encoding
it is much slower than restoring back to a 7.3.xx db.
Restoration from 7.3.5 to 8.1.3 took more or less 24 hours against
less than an hour from 7.3.5 db to any 7.3.xx db.

I don't have any idea why is it that way...

Anyone?