Quote:
Originally Posted by JRMichler
My engine stays closed loop at WOT up to about 4000 RPM, so no rich mixture penalty at normal speeds.
Throttle position does not matter, what counts is manifold pressure (or manifold vacuum if you look at it the other way). Keep that as steady as possible. With practice, you learn to enter the bottom of the hill 1 or 2 MPH faster and top the hill 5 MPH or so slower. All while minimizing the change in intake manifold pressure. The result, in addition to improved MPG, is that your driving gets smoother and your passengers all fall asleep so you have nobody to talk to.
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Closed loop does not mean its more efficient. Stoich AFR at higher RPM generates massive amounts of heat which causes knock. Your knock sensors of course will pull timing to avoid damage but this behaviour dramatically reduces your engines volumetric efficiency. Best acceleration method would be open loop with slight enrichment of ~13.5:1 at 3000+ RPM with additional spark advance for gas engines to keep EGT in check. Also there is something called tip in enrichment. Its basically change in throttle position vs time. The faster you hit the throttle the wider injector pulse width becomes to allow more fuel to be mixed. Most manufactorers disable tipin above 3/4 manifold pressure (engine load) though.
Of course the best method would be to just avoid such ungodly engine speeds all together. 2000 rpm is the engine speed that most EFI street engines produce their secondary torque peak at. So for accelerating, keep it at 2k rpm and vacuum as low as possible (load near 90%) and you will be fine.
Most efficient driving is non stop driving. If you are idling you are wasting gas.