It has been a awhile since, I have seen the forum...busy working on a wasteheat recovery stage(starting about 10 years ago).
As many of recall was look at the turbo unit on the Titanic and noted how small the
engine for the horsepower delivered(downside was with a single pass in 1911,at least
that translated out to only half the horsepower of piston engine.)
The aircraft mechanic had junk APU turbine laying around shop and thinking Doble was up to something on his turbocharger since a turbo will out pump a piston hands down.
Now the problem was could a turbo pump 4-6times faster than the exhaust on that steam engine.(in the course of things you are 100% recirculation give or take the steam trap stripping 10-15% of the steam as water)
The is connected with chain or gear to get redline match redline and at low speed is piston steam engine is like the electric motor on the doble turbocharger..the as speed build speed builds the steam takes over develop 2-3 to times the horsrpower of the piston engine using volume instead of pressure to it.
Well plug into an unmodified gas turbine you did too good of a job pumping as backpressure om the steam engine jumped to 65psi.
Shoots hell out of the steam piston flowbench rate.
To reduce the backpressure you needed a link in a control on the unit to adjust the cutoff down to something that the piston could live with for backpress and/or
rework the boost ratio to so the turbine powerwheel maxed out at about 20psi of back pressure on piston engine.
At the rate that piston steam development goes at,Cyclone looks like a hands down winner with 30% efficiency on new build.
At the same time, retro build on Victorian technology engines already can do same on efficiency as well with my turbo unit.The question is how many antique iron guys would be upset with someone adding in a "Titanic turbocompound" unit for about 3times the horsepower on the same steamrate and a lot slower respond time with throttle changes.

Anyone interested in building one of these "Titanic turbocompound" check with Peter Carlilich at Relaible Steam for the plans to his 5hp turbine.
Modified it by installing a t3 turbocharger powerwheel and installed a entire t15 for the gas generator with the wastegate diaphram controling the cutoff.
As a note a t3 with 30psi on the power wheel will develop 35hp.
in case someone was interested in plugging in a 5hp piston engine on some the steam funcarts,motorcycles, and tractors I saw guys build in meet videoes.
Not sure if I will ever be able actually see you guys in person..age tends to do that to your traveling abilities.

After finishing with the turbocompound using reliable steam"s gearbox for 200 lbs/hr flow on the turbine.(at the boiler at least, because of multi pass recuirculation the turbine themselves actually see 4-6 times that).
It became obvious that turbine is in the "sweet spot" on psi range of 20-30 pound.

And that all the kit built model turboshaft/prop engines used in the RC aircraft circuit were in fact built using garrett gt20 turocharger turbine wheels and compressor wheels.You end up with a 7.5 hp gasturbine the size of full size car starter motor.Which are also in the sweet spot at 20-30 psi in thier turbines.

There is the makings of a stand alone steam turbine for a go- cart or garden tractor that will use 7.5+.The heavy duty steamer guys will tell you that air has different expansion rate than steam,so that the steam power number could tune
to out double the hp with half the temperature of air.Because power wheel is a free turbine you have a built in torque convertor to work on output shaft spinnning at 5000-8000 rpm full load....at least on props running 30 pounds of thrust.
At this point still trying to make up my mind on whether to experiment with a another turbocompound engine with the unit or to combine cycle my 14hp diesel Kubota.

With the addition of a second planetary gear the output shaft could be direct drive on a Victorian steam engine.In case someone was to pursue build a titanic
turbocompound unit for their steamboat running a Kitchens rubber (British knew enough about steam that in the 1920's they built a directional thrust reverser
still see them today on jetboat nozzles and jet aircraft with reverser clamshells).

In the same vain as the Kitchen rubber on a non revervable engine.The ATV,gocart,car or ? can go with CVT belt drive like is used in place of hydrostatic
on many light equipment and vehicles today because of the sheer power other varible speed transmission demand.At risk of over general most are pegged "average" mid point for final drive ratio.Then the transmission go roughly from
2to 1 over and under that ratio.Like a MTD lawn and garden tractor or snow blower.
General Transmission is as big a name as Eaton is on the rearends.
And recent years there is even heavy equipment go to them as far torque loads they can handle ,those hydro still has an edge if you need torque like a piston steam engine or electric motor.But if you need belt drive it is the best out there for the price.