Don't confuse airspeed measured in knots vs mph. 330knots is about 380mph. Most aircraft airspeed is measured in knots.
I realize that Airspeed is usually measured in knots but ground speed specs are usually in MPH. I was thinking of a hopped up version of the A6M that was designed to compete with the Corsair which had set a new record of 405 MPH. I looked it up. THe A6M5 was fitted with a supercharger and was capable of speeds over 400 mph but only in a dive. there was a high speed version that was proposed (A6M8)that would probably have broken 400 MPH but it was never completed.
That'll teach me to rely on memory when the slow leak in my head starts acting up.