View Single Post
Old 07-08-2008, 06:05 PM   #6 (permalink)
garys_1k
EcoModding Lurker
 
Join Date: May 2008
Location: Motor City
Posts: 89
Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by mechman600 View Post
An engine is most efficient at WOT at peak torque RPM, in terms of energy produced compared to fuel burned.
Sorry, but minimal BSFC is almost always found at lower engine speeds than torque peak and at about 80% of peak load. At WOT you'll have power enrichment and, in some cases, spark retard if knock limited.
Quote:
Originally Posted by mechman600 View Post
I just came back from a road trip where I drove the steepest, hilliest highway known to man, the Coquihalla (BC, Canada). Lots of time is spent going up 8-9% grades (to 2 summits) and coasting down the backside. Fuel economy always ends up being the best in this situation because the engine is working at peak torque uphill, and coasting down (using zero fuel).
If that was the case then we'd all tow boat anchors when accelerating just to increase loads as much as possible and get better FE. We don't because higher power demands from an engine won't get us better fuel economy.

Fuel use increases with power, so the more power you were making climbing those hills the more fuel, pounds per hour, gallons per mile, you were burning. It's true that brake secific fuel (pounds of fuel used per horsepower produced) will be better at high loads, but that's kind of a red herring. The first thing you want to do is reduce the power demand as much as possible, THEN you want to go for more volumetric efficiency (reduced throttle/pumping losses) at that power.
  Reply With Quote