Originally posted by Angus
From Kurfurst:
"From what I have seen, the P-51D and 109K had very similiar total drag, reaching very similiar powers on similiar powers, at least near ground level."
The 109K peaked at some 2000 hp right, and had lots of power at S.L.
So, the P51D peaks with 1690 hp.
Or do you refer to the less boosted 109K????
Be careful Angus with that 2000 HP. Lrrp2 always accuses me of 'cheating' when I am lazy and write HP instead of PS. There were about 1% difference between the two, but still...

Now what I had in mind is the +25 lbs (1960 BHP at SL) Mustang D with wingracks (379 mph at SL), and what 'Leistungen 8-109 K4' noted as SL speed of the 2000 PS (about the same power if we note PS/HP difference), 377 mph. You see it's very similar, though w/o the bombracks the Mustang would be faster. OTOH, the Mustang was tested w/o paint either, that's quite a bit of drag and weight - if you recall those stripped Ju86 intercepting modded Spits - so on equal footing, no paint/no bombrack, it's the same again.
With 1690 HP, and the usual wingracks, the Mustang IV was credited with 354 mph top SL speed, but there's hardly any comparably powered 109s...
the uglier G-14s were good for 568kph/352 mph at 1800 PS, whereas the low-boosted 109K would do 370mph with 1850 PS.
BTW if you are interested in that Mustang IV tests, I can happily send over the original, though I think it's also found on MW's site :
2. Condition of aircraft relevant to tests.
2.1 General. Photographs of the aircraft are attached to the present part of the report.
The following were the chief external features:-
Six .5" machine guns in the wings, ports and ejection chutes sealed with fabric.
Camera gun port in port wing, sealed with fabric.
Multi ejector exhaust manifolds with shroud-plates.
Air intake in nose with internal ice-guard.
Aerial mast without external aerials.
Bead sight in front of windscreen.
Air filter intake in lower left cowling.
Faired bomb racks under the wings.
The aircraft was not painted. The under surface of the wings back to the main spar and the whole of the top surface had been coated with a smooth composition, the joints being filled and the remainder being bare metal. The fuselage was left with the bare metal except for a matt anti-glare finish on the top engine cowling. All other parts of the aircraft were also bare metal, except the elevator and rudder which were fabric-covered and doped.
In order to obtain adequate cooling, level speeds were done with the radiator duct flap set to a gap of 8½ inches, as coolant temperatures were excessively high with the normal setting of 7¼" gap.
2.3 Loading. The tests were made at a take-off weight of 9480 lb. with the C. of G. at 100.2 ins. aft of the reference axis. This corresponded to a typical loading with no fuel in the auxiliary fuselage tank and no external tanks or bombs. http://www.spitfireperformance.com/mustang/tk589.html