Doesn't have to be balanced to crank but helps.
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The reason people don't like to do it is because for normal road driving it can be a pain in the ass in most cases you need to adjust the revs to idle at around 1100k
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From what i have read up on some of various forums about lightening the flywheel they don't recommend it on a turbo.
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Something to do with the turbo spooling up a lot later but cant remember the full facts on it.
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All i know is from what i read it put me off doing it 100%