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Retarding the intake timing in those so-called "Atkinson" engines is often pointed to increase their efficiency due to a reduction of the pumping losses, but the low-end response gets awful. The static compression ratio is also usually raised in those engines, but the dynamic compression is decreased due to the decompression resulting from the retarded intake timing, so in theory they don't become more prone to detonation issues. Meanwhile, advancing the intake timing seems to make sense due to the improved low-end response, thus benefiting the use of higher gearing at lower RPMs while cruising.
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