So there seems to be discrepancies in the transient dyno testing, but and this is an insane but IMHO, it could be down to the Chev engine being near the bottom of the performance window.
From Adcafe:
''Where the two engines that were tested in the USA fit within that tolerance may also explain the differences recorded at AVL, with the Chev believed to have been at the lower end of its performance window.''
Why the **** weren't the engines that were sent over for testing both the same.
Action from February's Bathurst 500 The category concluded the second of two much-hyped transient dyno tests with the two engines
speedcafe.com