Quote:
Originally Posted by ichiban
oh and clived, i'm not understanding where this negative load is coming from, the engine cannot transmute a negative load to better fuel efficiency, iono i'm just not getting it, if i'm just stupid right now, please enlighten me XD.
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I believe that by "negative load", he is referring to pumping losses. Basically, when an engine is idle, the butterfly valve is basically closed, which limits the amount of air that can enter the intake manifold. This limited air, plus the intake stroke of the engine creates a negative pressure (vacuum) in the manifold. So, on the intake stroke, the engine has to work harder to fight this vacuum to pull the air into the combustion chamber. Again, you can see this in effect while coasting in gear vs out of gear.
While in gear, the pumping losses will limit how fast you can coast, because the pumping losses are affected by the current gear you are in.
While out of gear, your costing speed won’t be affected by any pumping losses.
If you test this, you should be able to clearly notice the speed at which you can cost while in gear vs while out of gear. Of course, like mentioned by Jeef Beef, coasting in a higher gear minimizes the effect of pumping losses because the gear ratio is very low, like 1:1 in 5th and like .8ish:1 in 6th. Compare that to 1st which is like 4.something:1, meaning that the engines pumping losses are being multiplied by > 4.
It's worth noting that the 128i (N52B30), or new 2011 135i (N55B30) probably doesn't even have a butterfly valve like most cars do, because I believe the Valvetronic system on these engines uses the intake valves like a butterfly valve: i.e. changing the lift and duration based on the specific situation. I believe the ECU with these engines minimizes pumping losses while at idle/low RPM. It would be interesting to compare the coasting speed of an N54B30 vs an N55B30 to see if Valvetronic would affect this.