Originally Posted by 360view
Confusion abounds in “gear ratio” as regards good fuel economy.

I suggest talking about MPH for each 1000 rpm, which takes everything into consideration, including tire diameter.

As regards getting the “right camshaft grind” for fuel economy, that is especially tough.
Today “variable valve timing” certainly improves late model engine fuel efficiency
but adjusting “ground in camshaft values”
down to what VVT is truly doing to the valves in today’s “real world”
is nearly impossible because even today’s 1800 page FSM
does not have tables about what modern PCM software commands are making happen to lift and duration.

There is another 10% fuel economy improvement if the air to fuel ratio goes from 14.7 to 18 or more.

There is an old Autospeed.com article about the early year Australia spec Honda Insight
and how at steady cruise speed on a level highway its air to fuel ratio would lean out to 25 to 1.




I like to think in terms of "displacement per mile" for example a 400 CID engine with a 2.28 gear ratio would have the same displacement per mile as a 200 CID with 4.56 gear ratio (tire diameter and such all being equal). They would have roughly the same performance all else being equal and in this case neither would be quick off the line but both should run satisfactorily at cruising speeds. If both engines were of the same design they would both have roughly equal air volume and speed in the ports. The 400 CID engine turning 1500 revolutions per mile would inhale the same air as the 200 CID engine turning 3000 revolutions per mile.

I am not causing global warming, I am just trying to hold off a impending Ice Age!