Quote:
Originally Posted by redpoint5
I get the impression that turbo charging a smaller engine is no longer the fuel efficient way. Perhaps due to the lower compression ratio?
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New turbo engines have relatively high compression. Plus direct injection, which theoretically gets you much better idling efficiency.
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I think the real problem is heat and load. A small turbocharged engine, when at idle or cruising below boost threshold in relatively mild operating conditions, will get economy similar to (but not as good as) a non-turbo engine of the same size.
Add heat soak and load and etcetera, and that goes away. I've been able to get better numbers out of Ford's turbo four in the Explorer than the V6, but only by really trying. Drive both the same way and the difference is undetectable.
Most economy tests feature milder drive cycles than the real world, so on something like the NEDC, downsized turbos can slip through.
I think the EPA test is more realistic. And more difficult. Which is why the Chevy 2.7 isn't getting great numbers.