The 908 engine had chain-driven cams like a 911, unlike the smaller 8-cylinder 753/771 or 912 (917) engines. By the late 1960's, very few racing engines still ran chain-drive cams.
The Type 908 used a 3-litre flat-8 engine which was almost entirely new, though it used a few Type 906 racing engine components.
With conventional wastegated turbochargers or fixed geometry turbochargers (FGT), a turbine flow area cannot be adjusted during operation.
Knocking is abnormal combustion in which the air-fuel mixture ignites prematurely due to exposure to high temperature and pressure, creating an unwanted high-frequency noise. When the compression ratio is increased, the temperature at compression top dead center (TDC) also rises, increasing the probability of knocking.