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My reading of the excerpt from the SAE article is that they are talking of the wastegate controlled engine, and the 'boost pressure' is the total pressure being exerted on the cylinder walls.
(1.0 bar from the atmosphere and the additional air charge of 0.7 bar for a total of 1.7 bar)
From the graph of boost vs engine speed if you subtract 1.0 bar the engine performance makes sense.
[Turbo lag from 1000 rpm (with 0.2 bar) to 2000 rpm with (0.7 bar), and wastegate controlled boost of 0.7 bar (from 2000 rpm to 4000+ rpm)]
Just a little different interpretation of the definition of boost pressure (in the SAE article) from what we typically define as boost pressure.
Essentially the same graph, in greater detail (with boost expressed in millibars, as the additional amount of pressure over over atmospheric pressure) is attached below.
It is from the W123 FSM, Section 09-450 Functional description of exhaust gas turbocharger with aneroid compensator, on Page 4 of the pdf.
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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022
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