The gas mileage for a 1993 Chevy G20 conversion van with a V8 engine is notoriously
poor. You're unlikely to see anything better than
8-12 MPG, and it could easily be lower depending on the van's condition, the size of the V8 engine (different V8s were offered), how it's driven, and the weight of any added features or modifications. Factors like tire pressure and driving style also heavily impact fuel economy.
Think of it this way: it's a large, heavy vehicle with a powerful engine not designed for fuel efficiency. Don't expect anything close to the mileage of a modern car.
