It can be done. Even Mercedes sells a E200NGT which is essentially an E200 Kompressor able to run dual fuel: Petrol and NGV.
NGV is ideal as it has a much higher octane than petrol which allows high compression/boost pressure and make more power. The reason why Saga taxi's make less power with NGV is because the engine is setup to run petrol which does not take advantage of NGVs higher octane.
NGV is ideal as it has a much higher octane than petrol which allows high compression/boost pressure and make more power. The reason why Saga taxi's make less power with NGV is because the engine is setup to run petrol which does not take advantage of NGVs higher octane.