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The Spitfire was a short range absolute high performance machine, fitting the Griffon engine kept it at the front in performance. For the P51, it relied on the low fuel consumption of the Merlin while cruising to rendezvous point and on station as an escort plus the trip home coupled with its prodigious performance on max boost in combat. I suspect that the Griffon would have made it slightly faster with a slightly better rate of climb but it would have used much more fuel while cruising due to increased swept volume and increased drag due to weight and frontal area. A Griffon powered P51 would outperform a Merlin engined one in almost every area except the one that made the P51 a game changer and that is its range.
The answer to the question lies in the fuel consumption of the Griffon v the Merlin while in cruise mode.
I was discussing purely from a theoretical point of view. The Griffon dry weight was approx 150Kg more than the Merlin. To get 150Kg to 30,000 ft and keep it there uses power, the Griffon would have to use less fuel per HP than a Merlin just to complete the same mission. I understand what you mean, it is possible that the Griffon could cruise as economically as a Merlin but this only applies to the outward and homeward part of the mission, while escorting bombers it is simply a question of gallons per hour and I am sure the Griffon consumed more fuel, certainly on max boost/power it would. I read a discussion about Reno racers fitted with Griffons and the effects are marginal more power but more weight and frontal area means it is a matter of choice, I suspect the fastest is the one whose owner is prepared to take the biggest risks of a blow up. Also for a time contra prop Griffon engines were available when the Avro Shackleton was retired.The question I have about that is whether the cruise speed using the Griffon would have compensated for the lower endurance and sill have ended up with similar range?
Possibly not the greatest for bomber escort though.
I was discussing purely from a theoretical point of view. The Griffon dry weight was approx 150Kg more than the Merlin. To get 150Kg to 30,000 ft and keep it there uses power, the Griffon would have to use less fuel per HP than a Merlin just to complete the same mission. I understand what you mean, it is possible that the Griffon could cruise as economically as a Merlin but this only applies to the outward and homeward part of the mission, while escorting bombers it is simply a question of gallons per hour and I am sure the Griffon consumed more fuel, certainly on max boost/power it would. I read a discussion about Reno racers fitted with Griffons and the effects are marginal more power but more weight and frontal area means it is a matter of choice, I suspect the fastest is the one whose owner is prepared to take the biggest risks of a blow up. Also for a time contra prop Griffon engines were available when the Avro Shackleton was retired.
The P51D with max fuel load was at the limits of safety, adding the extra weight of the Merlin may just have been a mod too far and a complete re design required.
Or the loss of range would make it counter productive. As others have said the whole scene was overtaken by jet engines and increases in power due to improved fuels/supercharging. The Merlin 130 produced over 2000BHP which was the power output required of the Vulture/Sabre intended to replace the Merlin.So basically, technically feasible but the gains wouldn't be worth the effort.
The P-51H was certainly the fastest prop plane in service in WW-II and it could run down any other plane with out question, BUT it was far from the best fighter plane of the war. But that is a topic for some other thread.
Quote "I think the V-1650-9 in the P-51H was basically the same as the Merlin 130/131 in the Hornet."
Well no it was not the same engine at all. There were huge differences in the American made Merlin and the R-R made Merlin.
The Hornet's engines made 2050-2080 HP at war emergency power and about 1600 HP at Take Off Power, but well after the war in 1946-7.
The V-1650-9 in the Mustang made 1595 at Take off Power, but made 2218 HP at WEP. This last is a huge difference and can only be explained by some mechanical difference between the two engines. I have been told by pilots I met at the Oshkosh show that it was better quality pistons and or rods, but I have not been able to find documentation to explain the differences.
The P-51H was certainly the fastest prop plane in service in WW-II and it could run down any other plane with out question, BUT it was far from the best fighter plane of the war. But that is a topic for some other thread.
The Spitfire XIV was a dog with the griffon engine. Look how long it took them to sort out the numerous problems it had. Over one year between first flight and first kill in semi-operational service. They had to add huge area to the vertical stabilizer to counteract the loss of stability caused by the new prop. All in all, it was a handling nightmare and poor gun platform due to snaking.
P-51 Conversions with Griffon engines have either fitted entirely new rudders/stabes and or tail planes, or used the P-51H rudder/stabe. Several have also fitted entirely new wings to correct the Center of Balance problems to avoid adding weight to the tail end.
While there was an on going search for more performance in every nation at war, the practical limits of propulsion had reared it's ugly head and made designer's life very hard. There were no easy solutions to the myriad of problems.
The main differences were the supercharger drive system, the carby and the fact that the V-1650-9 used ADI and the Merlin 130/131 did not.
The Merlin 130/131 were being built late in the war. Like other 100-series engines. (of which the V-1650-9 was one). The big change with the 130/131 was the downdraft carburettor.