The Toyota manual gear ratios are ideal for a stock 1HZ powered vehicle at or below GVM. In particular, 5th gear is reasonably low to allow the engine to run at relatively high RPM when cruising at highway speeds.
With the addition of the Safari turbo or Safari intercooled turbo systems, the dramatic improvement in torque means that the engine does not need to run at such high RPM when in 5th gear. Moreover, the Safari turbo or intercooled turbo enhanced vehicle permits substantially higher vehicle speeds than stock - and this translates to even higher engine RPM. Indeed, the stock 5th gear ratio may no longer entirely appropriate for this application.
The Safari 5th gear is a direct replacement of the relevant stock components and results in a 20% decrease in engine RPM at any given vehicle speed when in 5th gear. For example at 72 mph (120 kph), the engine RPM is reducedd from 2870 rpm to a relaxed 2300 rpm. This seemingly minor optimization of engine RPM can have a dramatic affect on engine durability and reduces the engine's tendency for excessive fluid temperatures - both engine coolant and engine oil.
The Safari 5th gear optimization is arguably the perfect finishing touch to every turbocharged 70 Series armoured Land Cruiser.