The Wright Cyclone, was used in a number of Yank armoured vehicle’s M3 Stuart, M3 Lee/Grant, M4 Sherman and also the LTV Buffalo.
They were very popular with our lads in North Africa and the Far East, they had a big
‘eff off fan to cool them and would draw the air in through the vehicle.
Whirlwind, the Cyclone was a much bigger engine. The only tank application for it was the M6 Heavy. Now I think of it, I don't believe that the R670 (for the M3 Lights) ever got a nickname. There's also the Guiberson radial diesel that the US was mucking around with for a while until they decided to go all-petrol.
Except for the M10. Which has always thrown me, I'm trying to think what else was in the US Army Europe logistics system which was diesel.
As for the comet - perhaps a try by someone of an average height for the time given he cant get in
Probably a bit faster. However, my view is that it's all relative. If I can get out of a vehicle at a moderate speed, and another vehicle at good speed, I figure that a more WW2-sized person will get out of the first one quickly, and the second one very quickly. There are some exceptions. For example, opening the driver's hatch on T-34 will take time no matter what size you are, because of the need to unlock and lock it into place by use of a screw system.