Quote:
Originally Posted by thomason2wheels
Interesting questions stillsearching, my belief is that hanging a turbo of any kind on an ICE runningat normal mixtures and temperatures, no matter whether the turbo is sized correctly or not will result in a net loss of economy compared to the same nonturbo engine. The one exception is the lean burn engine smokey yunick developed. Can you think of any other configuration besides, the one i mentioned? Talking strictly about gas as i have very little knowledge or experience with diesels.
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I tend to agree, which is why I posted about a turbo bypass in the other thread. :^) That said the argument is exclusively that "the extra low rpm torque lets you hold steeper gears, shifting to a higher gear at lower speeds thus the system gives better mileage" than the displacement increase of 30% otherwise required to work the same. That's the ARGUMENT, I just don't know if it works as advertised, or how to discern which times it does vs it doesn't. The nature of it is that it's limited to lower pressure because compression ratios must remain as high as possible. 5psi ranges or so mostly help cylinder filling without necessarily causing any detonation risk. This is different than the technique of a very small 4cyl with high boost (14psi or more) which requires lower compression like 8:1, which damages efficiency when off boost. It's possible with the right design you could have both though if you added an octane booster (perhaps methanol) for "power mode" so you could keep high CR and the "light pressure" philosophy for all normal octane driving.
That said diesels almost universally 100% of the time increase economy with a turbocharger - more air = more power and more efficient burn, they dont require a fixed fuel-air ratio. The Saab LPT is for gas engines.
I hope to start experimenting on a vehicle in the future with a bunch of different strategies that i'm all posting about now as early research. I'm making a list of a bunch of different methods and hope to have a workhorse that lets me test most of them just on that one vehicle.