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Twin-Turbo 5.4L Four-Valve (17 psi)Our guess is the first thing people will notice about this power curve is that horsepower was still climbing rather rapidly at our shut-off point of 6,500 rpm. Had we not run out of available injector, both the HP twin-turbo system and the 5.4L had plenty more to offer. Still, any motor that pumps out 1,002 hp and 832 lb-ft of torque is plenty potent. Every bit as impressive as the peak power numbers was that they came at just a hair over 17 psi. Credit for the big power at a low boost level goes to the effort made to produce an efficient normally aspirated package along with the impressive twin-turbo system from HP Performance. The twin 67mm turbos offered full boost as low as 3,500 rpm (the lowest tested with the turbo combination) along with the ability to easily surpass 1,200 hp.