All I can ask is--what are you doing wrong with the Typhoon?
I tested it again....and then again. I even went so far as to verify it with the film viewer after recording one test flight.
I could reach 393 MPH at 6,000 feet with no difficulty in the Typhoon. Repeatedly, and on film (not like anyone reading this can't test it in 5 minutes on their own). The in-cockpit Air Speed Indicator is actually wrong slightly and showed my speed to be about 396, howver this is a discrepency of less than 1 percent. 393 is the figure I'll quote since its the worse of them.
Interestingly, I am making that speed with twice the fuel load you took. I did my tests with 100% internal fuel because that represents how the REAL airplane would have been flight-tested. Weight can do some funny things with airspeed, so perhaps you should go back and try it with a full load of fuel.
Even its indicated airspeed at 6K was higher than the 373 you claim it capable of.
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I submit that you shouldn't worry so much about the P-51. You seem to hate it and are in fact spending more time complaining about it than your apparent difficulty in reaching the Typhoon's best speeds--which is the real issue.
Some clarifications:
"Wouldn't expect a P51 to be only 1mph slower than LA7. "
Why not? The LA7 only has a speed advantage at very low altitudes; above 5K they're almost even and by 7500 feet the P-51D has a clear advantage. It has been that way since the LA7 was released a couple years ago, so I don't see why it would "surprise" you that they're about dead even at 6k.
"Bet we have a hybrid 51"
No. In fact, we have two of them--the P-51B and the P-51D. The P-51B is best at high altitudes, and the P-51D performs fairly well over a wide altitude range. The Allison-engine P-51 you refer to is vastly inferior to the Merlin Mustangs at any altitude.
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"So somethings outta whack. "
Yes--for whatever reason you aren't getting full speed (not even close) out of the Typhoon, and you're "barking up the wrong tree" as the saying goes.
J_A_B