KA NA record in Oz 282hp and another closer to 300 using 2.4L

while the US has the record for turbo 800+hp and it is still in its infancy

The Other engine that could make more if further developed using todays tech
is the famous FJ20 in JDM Formula 3 the 2.4L fed by twin carbs put out 280hp
at 8000rpm so possibly could flow more but is much heavier everywhere yet
for boost could match or even outperform the Mitus Evo 4g63 as it is better
bottom end did not require a balancing shaft due to its sheer beef.