Net weight change is hard to figure when going from liquid-cooled engines to air-cooled
because it's difficult to come up with numbers on total
installed weight, all the systems
required, for most liquid-cooled engines. Also the weight of the coolant is a necessary
number.
I found the numbers for a two-stage two-speed Merlin, IIRC either a P-51D or a Spitfire,
but I'm damned if I can recall where off the top my head. I'll think on it and have a look
round. Coolant and oil system capacities are as important as fuel in determining the
actual loaded weight, but for some reason most references don't include that info.
The R-2800-22/22W and -34/34W were the standard F7F engines and weighed 2,385 lbs.