If they are Bosio nozzles and made for your engine you should have no problems. All but one of the threads I have read on them including other internet articles all have had good reports. The reports are better idle/running and seat of the pants feeling of power. No one that I can remember reading has commented on mileage. Some have said they are not as quite.

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84 300D, 82 Volvo 244Gl Diesel