(I think this has been discussed before)
As we all know, in the OTL, the Allied gained air superiority of the Luftwaffe because the P-51B/C Mustang with its excellent high altitude performance and 440 mph top speed was easily out-performing the Fw 190A's and Bf 109G models during the first half of 1944, which resulted in huge losses of experienced Luftwaffe pilots.
But what would have happened if Focke-Wulf had been able to secure a supply or Jumo 213 or DB 603 engines earlier for the Fw 190D series? Imagine what would have happened had the Luftwaffe gotten the Fw-190D into service at about the same time that the P-51B/C started to enter USAAF service in early 1944--given the Fw 190D-9's top speed of 422 mph, it would have made the D-9 and P-51B/C almost equals in combat, especially in straight line speed. As such, my guess is that it would have taken longer for the USAAF to establish air superiority, and North American may have needed to develop a "high performance" upgrade to the P-51B/C with a more boosted engine to better out-run the D-9's. (Republic probably would have done the same with a higher-boosted P-47D fitted with the "paddle blade" propellers.)
As we all know, in the OTL, the Allied gained air superiority of the Luftwaffe because the P-51B/C Mustang with its excellent high altitude performance and 440 mph top speed was easily out-performing the Fw 190A's and Bf 109G models during the first half of 1944, which resulted in huge losses of experienced Luftwaffe pilots.
But what would have happened if Focke-Wulf had been able to secure a supply or Jumo 213 or DB 603 engines earlier for the Fw 190D series? Imagine what would have happened had the Luftwaffe gotten the Fw-190D into service at about the same time that the P-51B/C started to enter USAAF service in early 1944--given the Fw 190D-9's top speed of 422 mph, it would have made the D-9 and P-51B/C almost equals in combat, especially in straight line speed. As such, my guess is that it would have taken longer for the USAAF to establish air superiority, and North American may have needed to develop a "high performance" upgrade to the P-51B/C with a more boosted engine to better out-run the D-9's. (Republic probably would have done the same with a higher-boosted P-47D fitted with the "paddle blade" propellers.)