Part 3
Ferrari's first use of 4RM was in a prototype created in the end of the 80s, called 408 4RM (abbreviation of "4.0 liter, 8 cylinder, 4 Ruote Motrici", meaning "four-wheel drive").[15][16]
This system is based around a second, simple, gearbox (gears and other components built by Carraro Engineering), taking power from the front of the engine. This gearbox (designated "power take off unit", or PTU) has only two forward gears (2nd and 4th) plus reverse (with gear ratios 6% taller than the corresponding ratios in the main gearbox), so the system is only active in 1st to 4th gears. The connection between this gearbox and each front wheel is via independent haldex-type clutches, without a differential.[17] Due to the difference in ratios "the clutches continually slip"[18] and only transmit, at most, 20% of the engine's torque. A detailed description of the system (based on a conversation with Roberto Fedeli, Ferrari's technical director) has been published
