Quote:
Originally Posted by diesel_john
but the air fuel ratio on the diesel can be as high as 200 to 1. so at light loads i am pumping a lot of extra air for no reason.
what i want to do is reduce the effective displacement at light loads.
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Sorry to jump in this late.
The lean nature of the diesel is one of the 3 reasons they return more MPG than gas engines. The only way that reducing displacement could help a diesel is physically removing the friction of the parts (ie taking pistons and bearings out).
Some of the other posts are implying to use a turbo to eliminate pumping losses in a gasser, this is really not possible. To eliminate pumping loss vacuum you need to fill the cylinder with something, either air or EGR. If you go the air route you have to lean it out, if you dont then you have effectively just pushed the gas pedal farther to the floor as you are adding fuel to keep 14.7:1 A/F ratio. You dont need a turbo to lean out the mixture.
One thing you could do is advance the cam for an earlier intake opening so that the vacuum is smaller for a shorter duration of the piston downstroke. But this is opposite of the atkinson cycle so you couldnt do both.