something doesn't calculate right to me.
You have 340WHP , and that is a wheel dyno.
on our car powertrain loss is around 10-12% at max.
so going by that route , you are suppoused to see no more than 380bhp at the flywheel.
what is the compensation built into that dyno ?
also , can you please tell me if the data is raw or SAE ?
They are Fly wheel figures mate.. 
this is a DD dyno right ? so it measures wheel hore power and not flywheel.
basically then there is simple math of power loss added for compensation.
don't get me wrong , 340whp is very good , but no way that it can translate to over 400 flywheel hp on a fwd car.