They are just two different acronyms for the same engine.
F4 = Flat four cylinder engine.
H4 = Horizontally-opposed four cylinder engine.
Both refer to Subaru's horizontally opposed piston design, also known as a boxer-style engine. The main benefits of this style engine are that (1) the engine is naturally balanced and (2) it helps keep the center of gravity lower.
These guys are all full of it.... F4 stands for the upgraded version of the F1 motor that comes in the the race car... H4 stands for the 4 wheel drive system.... Geez you'd think all these guys with the "fast subaurs" would know this.... *snicker*
Resident Grumpy Old Man(Keith)
03 SRP 2.34L now with Spec C goodness
08' LGT Gears...