What kind of gas mileage would a 1977 el camino with 350chevy engine get?

A 1977 El Camino with a 350 Chevy engine would likely get very poor gas mileage by today's standards. You're looking at somewhere in the range of 8-12 miles per gallon (mpg), and possibly even less depending on driving conditions, vehicle condition, and the specific carburetor/engine setup. Factors that heavily influence fuel economy in these cars include:

* Engine condition: A well-maintained engine will generally perform better than one that is neglected.

* Automatic vs. manual transmission: Automatics tend to be less fuel-efficient.

* Driving habits: Aggressive driving significantly reduces MPG.

* Tire pressure: Properly inflated tires improve fuel economy.

* Vehicle weight: Added weight reduces MPG.

Keep in mind that these are estimates. Actual mileage will vary.