The challenge with the original Merlin was that it was so complex that RR could not build enough of them to meet the demand. So when Packard was contracted to build them they re-engineered the engine so that it could be mass produced. The Packard engineers said that the British method of engineering was to make 5 parts to do the job of one part. Once Packard got going they built the majority of the Merlin engines. When it was originally built in the late 30s it made around 900 hp, un-supercharged and on the British 87 octane gas. Every time the US would send England higher octane gas, the horse power on the Merlin went up. They added superchargers and then two superchargers and then they made them two speed. At the end of the war when the US was shipping 145 octane gas the Merlin was making 3400 hp +!
The Allison got a bad rep when they took them out of the Mustang. Being that the Allison V12 was being paid for by the Department of Defense and they had a real thing for turbo charging, which was in its' infancy, so they made Allison work on developing a turbo charged engine. Allison wanted to follow RR and go with twin blowers and a two speed drive but the Gov. made them stay with the turbo program. Yes there were supercharged Allisons but they were never the equal to the Merlin. Of course they did finally start getting the turbo set up to work but the war was over and every thing was going to gas turbines and jets.
Unlimited hydro racing went to gas turbines years ago but there was a guy in Ohio that developed a twin turbo Allison with electronic fuel injection and at one time he was kicking the tubines a$$s!!
Rex
