If you go with a Hartzell C/S prop, you do not need
the 4" extension, as the "extension" is already built into the Hartzell
F2YR hub. See Hartzell´s application guide here:
As for the other C/S prop brands (MT, Whirlwind,
???) I do not know whether or not an extension is needed.
If you install a F/P prop, you will need the
extension in order for your cowl to clear the engine block / cylinders / starter
motor / alternator and what have we all.....
Tim Jorgensen, Denmark
360MKIIOBFB / 98%