Fuel Econ and Hiway Mode

[Jeremy Gonyou]

OK, Max, I gotcha now. EGR has higher pressure than the charge at part 
throttle.  Compresses charge slightly. Damn those throttles!  I always 
assume wot :)



>What I meant is this,
>	The effective compression ratio changes with throttle position.  The
>closer to atmospheric pressure in a manifold(in a naturally aspirated
>engine) the higher the effective compression ration.  The more stuff you
>have in the cylinder the higher the pressure in the cylinder, regardless of
>whether or not it is compressible.  At idle or part throttle your 11.5 to 1
>454 is obviously developing less cylinder pressure than at a point when the
>throttle is wide open(at the moment before ignition).  Yes the actual
>compression ratio is the same but when you compress a gas which is at less
>than atmospheric pressure the end pressure will obviously be less than if
>you compressed it the same amount but had started at atmospheric pressure.
>This causes a severe loss of efficiency(generally, increased compression
>ratio increases efficiency (freshman thermo)).  Its why an engine is more
>efficient at WOT.  It may not make a huge difference but to say that there
>is none, I would have to disagree.  (but I have been wrong before;-)
>
>I believe this is why a small engine running at max output is much more
>efficient than a large one running at half even with more reciprocating 
>mass
>etc
>
>Max
>
>
>No flames please;-)

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