Basically, faster (either) engine runs, the more fuel it burns.

A situation that gets the throtte (gas engine) open wider is conducive to better fuel economy, too, as it reduces pumping losses

Both are combined when NOT shifting at redline. Perhaps some recall VW's "upshift" light from the 1980s--it suggested REALLY short shifting.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles