Göran Josefsson's research while affiliated with Volvo Car Corporation and other places

... As identified in several papers [1,123,134], and frequently referenced during the newer engine developments, downsizing works well when high levels of tumble are used, allowing improved combustion stability, increased EGR / dilution tolerance and reducing knock sensitivity [192,193]. Bandel et al. [136] suggest that charge motion of around twice thencurrent levels would provide sufficiently fast and stable combustion to allow increases in compression ratio and/or reduction in enrichment for component protection. The rationale is that use of a suitably-matched turbocharger enables boost pressure to be raised to overcome any loss in volumetric efficiency inherent with ports designed for charge motion in preference to high flow coefficients, making high-charge-motion port design synergistic with turbocharging and downsizing. ...