3,75 running great
AO Car Of The Year Winner 2015
Join Date: Dec 2003
As said above, when in gear and your foot is off the gas the engine doesn’t consume any fuel. BUT only above certain revs. When the revs are dropping, the ECU slowly restores some limited fuel supply to the engine at about 1200-1500 rpm or below to keep it running and make the transition to idle as smooth as possible.
You can try it for example in third gear; release the pedal at 2500 rpm. Consumption is zero, revs are dropping 2000 - 1800 - 1500 - 1300 and somewhere here you will start to feel slight vibration as the fuel supply is smoothly restored, the car passes into idle and it will actually never stop even though you don’t touch the gas pedal. The idle fuel supply is restored much sooner than revs hit idle to keep things smooth. But above 1500 rpm most cars have zero consumption when off the gas.
And emission control is another problem. Drive in 5th at 4k rpm an highway and shift into neutral. It will take good 4-5 seconds for the engine to drop the revs to iddle. The fuel is not cut off inmediately, but slowly, in the controlled way so that the emissions are as low as possible under any circumstances. The same happens when you lift off - the fuel is cut off, but there is still some very limited injection for a few second to stabilize the emissions. Thats why present cars have so poor throttle reaction. The fuel control and air supply are actually not controlled by your foot but ECU filters your instructions according to its program..... So at the first few seconds after lifting off, there still is some very limited consumtion. But we are talking VERY about very low amounts your board computer cant actually display.
147GTA,Grigio Metallico,Imola leather,3.75l conversion,ported heads,F575 TB,Carbon plenum,Stainless manifolds,EQ pipes,Supersprint silenced cat back,18" GT multispokes,KW V3,Galfer 6pot 355mm,Brembo sport rear
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Last edited by gotcha; 12-10-10 at 19:45.