Quote:
Originally Posted by Ecky
Most newer engines run a higher static compression ratio than can be readily (or efficiently) controlled by ignition timing alone.
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Even though some flexfuel engines didn't resort to such an "extremely" high compression a few years ago, and Fiat introduced intake and exhaust VVT to a SOHC engine in the "people's car" segment when it released the GSE/Firely 3-cyl 1.0L and 4-cyl 1.3L in Brazil. Some folks often say the VVT was meant to provide a lower dynamic compression, yet it doesn't seem to be really the case, otherwise the power and torque difference would be much greater on gasoline compared to ethanol.
Quote:
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Sufficiently advancing or retarding ignition timing effectively limits how much air gets into the cylinder, reducing the absolute peak cylinder pressure to a manageable number, while also allowing for very high expansion ratios.
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AFAIK adjusting the ignition timing works to overcome turbo-lag too, but I'm not sure why it would limit how much air gets into the cylinder.