SIC - incorrect. Well, yes you can log anything you want but if you intend to use towards the aeronautical experience for additional ratings or certificates it has to be legal time. Logging SIC in a part 91 Piper Cherokee doesn't exist. The aircraft is single pilot according to the type certificate and the operation does not require a second pilot, such as 121/135 operations.
If you are boarding a plane and don't understand if you are PIC or SIC, then you're just a passenger and don't log anything. There are numerous posts, discussions and publications that address this.
And you seem to be another one. 61.51. Learn it. Love it.
(f)
Logging second-in-command flight time. A person may log second-in-command time only for that flight time during which that person:
(1) Is qualified in accordance with the second-in-command requirements of §61.55 of this part, and occupies a crewmember station in an aircraft that requires more than one pilot by the aircraft's type certificate;
or
(2) Holds the appropriate category, class, and instrument rating (if an instrument rating is required for the flight) for the aircraft being flown, and
more than one pilot is required under the type certification of the aircraftor
the regulations under which the flight is being conducted.
And guess what, there's even a regulation under which said flight would be conducted. 91.109
(c) No person may operate a civil aircraft in simulated instrument flight unless—
(1) The other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the aircraft being flown.
(2) The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot; and
Safety pilot = required crew. But it was nice of you to chime in with your expertise.