[Turk]

I calculated, if there is ZERO allowance for density altitude and we used the 4400 for elevation the HP loss is almost 54 HP. Thus making the sea level numbers around 408 HP at the rear wheels, and adjusted for the 20% for the rear wheels we are right at 490 HP at the fly wheel.
Not bad for a engine that gets 14.536 MPG at increased speeds.

Now for some reason the density altitude was at 5000, the numbers come up to 500 at the fly wheel.

TURK
I hope this helps.