Even though Kirby said it couldn’t be done, I got warm compression numbers! (I cheat because I don’t have an AC compressor.)
Car was 190F coolant temp when shut off. It took me only 40 mins to remove throttle pedestal and all plugs, and rig throttles to be wide open, and remove fuel pump relay. Then took me 20 mins to collect numbers. Engine coolant temp was 160F throughout test.
Oh, and I’m quite happy with my numbers!!! 215 - 225.
(1988 xjs V12 with about 50K miles)