The incredible power output of the Viggen's engine is primarily attributable to the larger turbocharger, which produces maximum boost pressure of 1.4 bar, or a full 20 psi, and is assisted by less restrictive air intake pipes and a performance exhaust system. Although only 15-16 psi of boost pressure may be required to achieve maximum power and torque at or near sea level, Saab's Trionic 7 engine management system allows the turbo to produce up to 20 psi at higher altitudes to compensate for less dense air. The result is maximum power is available at altitudes approaching 10,000 feet.

psi of one turbo does not equal psi of another turbo in terms of power that it outputted. on a larger turbo you don't need as many psi to make the same power.