I just recently installed my vacuum gauge and am hoping to improve my mpg's. Mainly this gauge allows you to read the throttle, which is the pressure at the manifold. The pressure is proportional to the air density, and with a fixed air/fuel ratio, this is proportional to the cubic millimeters of fuel injected into the engine, per revolution of the crankshaft.
Driving at 2/3'rds WOT (wide open throttle)--corresponding to 10 inches of mercury-- is most efficient for the typical gas engine, but staying between 85% WOT to 40% is nearly as efficient for a good range of rpm's.
Below is a bsfc chart for a typical 4 cylinder gas engine:
(taken from this thread)
It surprised me how efficient these engines run at higher rpm's. i assume this chart is for a oversquare short stoke engine; long strokes would be shifted to the left and better for lower rpms. my subie is slightly oversquare, and so i guess i won't hesitate to accelerate at 3500 anymore for fuel concerns.
So, I'm going to assume this for my car:
--Most optimal operation near 2/3 WOT is from 1500 to 3600; I'll try to use this range when power is required (getting up to speed, hills).
--Higher throttles ~80% WOT, will work better at higher rpm's; over 2500.
--At lower RPM's (less than 1750) apply even less throttle, under 1/2 WOT but over 40% WOT.
--Idle seems to be a little under 1/3 WOT (10 inches of mercury) and efficiency near this pressure is 50% that of the peak efficiency.
Driving at 2/3'rds WOT (wide open throttle)--corresponding to 10 inches of mercury-- is most efficient for the typical gas engine, but staying between 85% WOT to 40% is nearly as efficient for a good range of rpm's.
Below is a bsfc chart for a typical 4 cylinder gas engine:
(taken from this thread)
It surprised me how efficient these engines run at higher rpm's. i assume this chart is for a oversquare short stoke engine; long strokes would be shifted to the left and better for lower rpms. my subie is slightly oversquare, and so i guess i won't hesitate to accelerate at 3500 anymore for fuel concerns.
So, I'm going to assume this for my car:
--Most optimal operation near 2/3 WOT is from 1500 to 3600; I'll try to use this range when power is required (getting up to speed, hills).
--Higher throttles ~80% WOT, will work better at higher rpm's; over 2500.
--At lower RPM's (less than 1750) apply even less throttle, under 1/2 WOT but over 40% WOT.
--Idle seems to be a little under 1/3 WOT (10 inches of mercury) and efficiency near this pressure is 50% that of the peak efficiency.