Piston engines got pretty wild before turbines eventually took over the world. The most efficient ones were more efficient than today's turbines in terms of BSFC[0]. One of the most interesting to me was the Napier Nomad[1], which used turbo- and super-charging. However, the turbo had secondary fuel injection and effectively ran as a turbine to drive the compressor.

[0]https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... [1]https://en.wikipedia.org/wiki/Napier_Nomad

Gas turbines aren't generally noted for their efficiency, but rather:

- Power-to-weight ratios. Critical in aerospace applications.

- Long duty cycles. Everything spins, reducing wear-and-tear relative to reciprocating designs. Maintenance on piston engined aircraft during WWII was a major logistical concern.

- Raw speed. Supersonic flight requires high rotary speeds, and the few propeller-driven aircraft which achieved this had ... issues. Ground crews and pilots suffered health effects from the noise alone, and notoriously often flat refused to work with the XF-84H "Thunderscreech": <https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech...>. At near-supersonic speeds and above, propeller blade tips themselves break the sound barrier, losing aerodynamic flow over the blades, making quite a racket, and greatly reducing efficiency.

Propeller-driven planes remain more efficient than jets in many instances, though last I checked US military forces rely on turboprops over reciprocating engines in virtually all instances, possibly excepting some civilian-based (e.g., Cessna / Piper, etc.) trainer or observer variants.

Those exhaust driven turbines didn't just drive the compressor like is typical with turbochargers, but was also mechanically linked to the crank shaft so the turbine contributed to the overall power output of the engine directly, not just by forcing more air into the cylinders. That's what made them "turbo-compound."

The youtube channel "Greg's Airplanes and Automobiles" has a nice video about turbo compound engines.

Speaking of turbines and fire apparatus, back in the 60's a few jet turbine powered engines and one ladder truck were made: https://www.aeroflap.com.br/en/when-fire-trucks-used-boeing-...

Napier Nomad is one of my favorite engine designs. More info at https://oldmachinepress.com/2019/08/05/napier-nomad-compound...