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Originally Posted by raubvogel
If turbos did not help with fuel economy they would not be used in 18 wheelers.
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Diesels are a whole different deal, even though nowadays as direct injection became more common on gassers a turbocharged gasser with direct injection may eventually reach a better fuel-efficiency than a port-injection one with natural aspiration within the very same displacement bracket.
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In the 80s the recipe to deal with boost was to add 30% more fuel. In more modern times, a wideband O2 attached to a FI system that is smarter than the average politician can do a lot. Add support for knock sensing (you could copy the old APC system if you want to be lazy, but nowadays you can do much better) and ensure your FI system can adjust ignition timing and boost on the fly, and you may have a good starting point.
FYI, I do not remember the last time I saw a factory turbo car without intercooler. I have seen people build their own forced induction, specially supercharged ones, without it but then again some think that intercooling and wideband O2 sensors are witchcraft, and the only approved fuel system is a carburator.
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When those Fueltech aftermarket programmable ECUs became more popular within the drag-racing scene in Brazil, carburettors started to get out of favor among street racers too.
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Most cars using turbo for economy have compression ratio around 11:1 nowadays. They usually are set to handle under 10psi of boost, but more modern fuel systems can push the envelope.
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No wonder nowadays I see many engine platforms which still resort to the good old port-injection for the naturally-aspirated versions, yet they switch to direct injection for the turbocharged ones.