P-40 vs P-51: How a Supercharger and an Engine Swap Split Two WWII Fighters

Why the engine decided everything

Both fighters started life with the same Allison V-1710 engine. The Allison had a single-stage, single-speed supercharger, so it lost power as the air thinned. Wikipedia’s P-40 article says this made the Warhawk a poor high-altitude fighter.

The early Mustang had the same problem. Its power dropped off rapidly above 15,000 feet (4,600 m), which made it unsuitable for the air war over Europe.

Then North American fitted a Rolls-Royce Merlin in mid-1942. That dramatically improved performance above 15,000 feet, and the Merlin-powered P-51B and P-51C entered production in June 1943.

Curtiss did build Merlin-powered Warhawks, the P-40F and P-40L, and they were more capable than the early Allison versions. But the P-40 was already an older design, and the line closed in November 1944.

Where the P-40 Warhawk wins

The Warhawk wins on timing and toughness. It first flew on October 14, 1938, and 13,738 were built, so it was in service in numbers while the Mustang was still a prototype. The Mustang’s prototype first flew on October 26, 1940.

It excelled at low-altitude air combat and ground attack. It was the primary fighter in the Southwest Pacific in 1941 and 1942, and it fought in North Africa and over China.

The Flying Tigers flew the P-40B and were officially credited with 297 enemy aircraft destroyed, 229 of them in the air. Their first combat came on December 20, 1941, twelve days after Pearl Harbor.

The shark mouth came from a photograph of a No. 112 Squadron RAF P-40 in North Africa. The RAF unit had borrowed the design from German fighters, and the Flying Tigers copied it.

For a longer look at where the Warhawk sits among American fighters, see American fighter planes of WW2. The P-40 Warhawk aircraft page has the full specs.

Where the P-51 Mustang wins

The Mustang wins on altitude, speed and reach. The spec panels list a service ceiling of 41,900 feet (12,800 m) for the Mustang against 29,000 feet (8,800 m) for the P-40.

They list a maximum speed of 441 mph (709 km/h) against 361 mph (582 km/h). Both are variant-dependent figures, so treat them as the panel’s headline numbers rather than a head-to-head test.

Range is the biggest gap. The panels give 1,650 miles (2,660 km) for the Mustang and 720 miles (1,150 km) for the Warhawk.

With external fuel tanks, the Mustang could accompany bombers from England to Germany and back, starting in 1944. That is the job the P-40 never had the range or altitude to do.

The Mustang began as a British order. Mustang Is reached the RAF in October 1941, and No. 26 Squadron became the first unit to fly them in January 1942.

The P-51D, with its bubble canopy and six .50 caliber Browning machine guns, became the definitive version. Mustang pilots claimed 4,950 enemy aircraft destroyed during the war.

The P-51 Mustang aircraft page covers the airframe in detail. If you want to see how it fares against other legends, try P-51 Mustang vs Spitfire or P-51 vs Me 262.

Both were piston fighters, not jets

A common mix-up is to treat these as early jets. They were not. The spec panels list one piston engine in each: an Allison V-1710-39 making 1,150 hp (858 kW) in the P-40, and a Packard-built Merlin V-1650-7 making 1,720 hp (1,283 kW) in the P-51.

That 570 hp gap, plus the Merlin’s better supercharging, explains much of the performance difference above.

Was the P-40 faster than the Zero?

At low altitude and in a dive, generally yes. The Flying Tigers’ P-40s were described as very sturdy, heavily armed, and generally faster in a dive and in level flight at low altitude.

The Zero could out-turn almost anything, so the P-40 pilots did not try to turn with it. Commander Claire Chennault taught a diving or slashing attack, then a dive away to set up the next pass.

The Zero also lacked armor plating and self-sealing fuel tanks, so a short burst from a P-40 could do real damage. That is the trade the Warhawk offered: it could not out-turn the enemy, but it could survive a fight and choose when to leave.

Did pilots like the P-40?

Many did, and mostly for one reason. Australian ace Clive Caldwell said it “would take a tremendous amount of punishment, violent aerobatics as well as enemy action.”

More than 200 Allied pilots became aces flying the P-40. Claims vary by theater, pilot training and tactics, so the number says more about how widely it was used than about a clean win over rivals.

So which one should you pick?

Pick the P-51 if the question is which was the better fighter. It flew higher, farther and faster, and it could escort bombers into Germany.

Pick the P-40 if the question is which fighter did the most with the least in 1941 and 1942. It arrived early, took a beating, and held the line in places where nothing better was available.

Together they tell a simple story about WWII aviation: the right engine at the right altitude mattered more than almost any other design choice.