peterc005, the O-235-F has the higher compression pistons.
I've been trying to find out what aircraft were fitted with the -F, G or J model engines with no success so far.
Edit: Success, the A152 Aerobat had the option of the "Sparrow Hawk Power Package" which upgraded the engine to -F spec which put the power up to 125hp and brought the TBO down from 2400 to 2000.......