340 Gets Terrible Gas Mileage

That seems normal for a vintage era "performance" engine. I think I looked it up once my 70 dart Swinger 340 is quoted as 13 mpg highway...that's with 3:91 rear. I knew guys back in the day with Chevelle 396's etc that said they never passed a gas station and that was in the 80's...with gearing keep this in mind, I have an 86 Mustang GT convertible with 2:73s, is it street able and highway drive-able? yes, does it launch hard at the track? no in fact its a 15 second car. Thing is its a cruiser and fun on the street and will do 140 on the highway.