4.0 OHV has been around since the 80's. It was available in the first Rangers. It went through many changes over the years, but the basics are all the same.
The 4.0 OHV stoped being used in 2000 in the Ranger.
The 4.0 SOHC was introduced to the Ranger in 2001.
The 4.0 SOHC was introduced in the Explorer in 1997.
The main differance is in the Cams/Heads. The OHV has a single in block cam where the SOHC has two cams that reside over the heads (one per side).
This moved the power curve up higher alowing the engine to rev higher and produce more HP (207v160). While the torque remains nearly identicle when ran on a dyno.
Both engines are very nice, but the SOHC has the advantage on the street while it can be debated that the OHV reighns off road.
(I'm sure there are other differances, this is just the major differance)
Imagine if sharks could walk on land... Scary.
1999 Long-Travel Ford Ranger XLT 4x4 4.0 4door
2007 F-150 5.4 FX4 SCREW