Which Was Better: The P-40 Allison or the P-40 Merlin?

The Curtiss P-40 was built with two significantly different engines. Most of these planes had the Allison V12 but there were also a couple of versions that had the Packard-built Merlin engine. 

Similar Engines?

The Allison V1710 and Merlin V1650 are very similar engines.

They are both liquid-cooled V12s with four valves per cylinder and both have sodium-filled exhaust valves.

The similarities are there because both the design teams are in the same era, working with the same technology and mostly using the data from the same sources. 

Comparisons

When comparing the two externally, the Allison comes out smaller and lighter. A Merlin engine in a P-40 has an empty weight of 150 pounds more than an Allison-powered one.

With equivalent fuel and ammunition loads, the Merlin-powered fighters were approximately 50 to 100 pounds heavier. 

The Allison can put out 1475 hp at war emergency power versus just 1300 hp for the Merlin. However, at military power which is the normal maximum, the Merlin comes slightly ahead with 1240 to the Allison’s 1150.

Which is Better?

In terms of core engines, both are very similar and produce the same power.

The Merlin, however, had a much better supercharger and intercooler. As a result, this led to better reliability. 

There’s no doubt that in terms of engineering, both the Allison and the Merlin are lightyears away from anything that was produced in the automotive world during that era.