Only reason I can think of for the paired rear exhausts is heat & flame too close to the airframe.
They do spit fire at times.
Didn't that aircraft have a lot of wood in its construction ?
(Something like that was called "the flying piano" for its wood content.)
Love the sound of a Merlin or Griffon flyover at speed. Nothing else like it.
Wonder what they'd sound like with an exhaust more like the old V12 Ferraris...?
As for the RPM, I would think the props are part of the equation.
And back in those days engines weren't apparently spun at high RPM in most applications.
Correct prop blade tip speed is critical. Can’t remember the exact speed ( think it’s around 320 mph) but I do know once you exceed it the blades tips will stall. As the speed / rpm is increased the stall works its way up the blade toward the hub. Same as spinning the tires for us car guys.
