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I gotta dis-agree with you, Feets. You will never see bsfc numbers in the .4s with any turbo engine(with the exception of direct injected engines). It's not all that uncommon to see .45 in a well thought out n/a engine.
The myth of economy with a turbo engine comes from, as previously stated, a smaller engine that is capable of making the hp of a larger engine. If you were to use that smaller engine in boost all the time though, you would be no further ahead in economy. It's the time out of boost with a smaller engine that you see your gains in economy.



Herb's old book shows bsfc in that range with water injection and turbos. I believe Booster is seeing that kind of results with his TT340, but he's spent 20yrs engineering that systems to be as good as any OEM setup for the street.

Would have to talk to Tom Vaught on tmf, but I wouldn't be surprised if Ford's Ecoboost systems are among the most efficient engines out there right now (they are direct injected though)

To the OP's concerns, if you wanted better mpg you'd probably replace that 440 with a boosted 318. OR, if you wanted to make 600hp with your 440 and have good street manners, you could boost it rather than put big heads and cam in it. Corky's book explains it well saying 'at best the turbo system is a mild restriction in the system under light load and will cause a small loss in efficiency'. The 'gain' in mpg is not over the existing engine but in any upgraded NA engine that would compete with it for equal power.

Last edited by furious70; 09/30/11 12:05 PM.
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