Surely we only have two variables here: pressure and temperature. So am I right in assuming that the only benefit of a more efficient turbo at a given boost pressure, is that it can create that boost with less heat as a by product?
yes.
pressure and temperature are connected by laws of thermodynamics (amateur science hat on)
for every psi increase in pressure, there's a known increase in temperature. Lots of Caicos are done ASSUMING ideal conditions, but confessors are never 100% efficient.
As compressor efficiency drops, more heat is added. This can be calculated too.
Efficiency in this sense is a reference to adabiatic efficiency or, how efficiently a compressor compresses air. Less efficient compressor, more heat created.
My scenario of a ct 26 at 18psi, it would be operating toward the far right of the efficiency map. Working too hard.
A gturbo at 18psi would be in the centre, well within its design parameters.
This would mean denser air potentially accomodating increased fueling (or more complete combustion of existing fuel) therefore more power. So the benefit would be much the same as adding an intercooler?
To flip that, hotter air is less dense. If you can avoid heating the air by compressing it, then yeah, its a win.
Additionally, does the greater efficiency / flow achieve a given boost pressure faster, thereby creating more power in a sort of indirect way by ramping up the whole boost / fuel curve more aggressively?
how quickly a turbo spools up is dependent on turbine and turbine housing design, size, and efficiency, andis also affected by compressor design and size. A large compressor will take longer to overcome inertia and spool up.
A smaller turbine housing will help spool a large compressor sooner, but will choke exhaust flow sooner too, so you lose out on top end performance.
At a given turbo speed, a larger compressor is going to be pushing more air. It may take longer to get up to speed, but at every point along the way it's pushing more air too. It's not as simple as saying one spools faster than another.
As a turbo spools up, at slow shaft speeds, initially it's off the map to the left, as it spools up it will do most of its work in the verge of the map.
Under hard acceleration, full throttle, lots of fuel, mid to high engine RPM, the turbo is gonna spin faster and efficiency moves toward the right of the map. If it's poorly sized, or incorrectly wastegated, at some point its gonna push all the way to the right of the map , like the ct26 at 18psi.
I blew up a ct26 in a scenario like above, but it boost was peaking at 22psi. Way off the map, and in choke flow (the compressor spinning so fast it just chops at the air, and can no longer compress it).
Or is there some other sort of fairy dust involved that I'm not aware of?
Yes. Black magic mostly.
