BB 440 Mileage?

I had a 69 Charger that I swapped in a rebuilt 440. Drove it to the Nats in 87 or 88 while a friend drove one of my other cars (71 Chally covert with a 318). Kept mileage records for both for the trip. The Charger got 19MPG round trip, including several passes down the track, back and for to the hotel, etc. Chally got 18 with no track time. Both cars had highway gears - 2.76s.