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Originally Posted by falcon_wizard
Can anyone share any experience relative to fuel consumption of a 10:1 motor versus 12.5 ? I am trying to understand if lowering the comp ratio will automatically result in worst fuel economy because of an inherent less efficient engine, or if careful tuning of the turbo on a built 10:1 engine can actually allow to maintain equivalent fuel economy (at equal performance) to a stock 12.5:1 by having boost coming on sooner and reach the same overall effectiveness (once spooled).
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It will be inherently less efficient. Raising the effective compression ratio by adding boost is not as efficient as raising compression. While everyone always talks about the parasitic effects of a supercharger, there are still losses with a turbo. Recall too that turbos add boost under load and are subject to turbo lag and boost threshold. Because the turbo requires energy to create boost, inherently having less energy means more rpms are needed to get to that threshold.
Remember too that manufactures will painfully innovate to get three more mpgs out of a car because going from thirty to thirty-three mpgs is a ten percent improvement, which gets them closer to government mandates, but is that really a big deal for a car enthusiast? Usually not.