What Is Good Gas Mileage?

dude the 318 was probably fine with the original heads. by plopping on the 360 heads you probably dropped the compression ratio down to 7:1. that right there killed the mileage. then adding a 4bbl hit it some more. then a duration cam (pumping extra gas/air into the 7:1 compression lol) did it even worse.

ideally for mileage:
1. light car = better
2. highest streetable compression. shoot for 10:1 for ezmode or if you are extremely good at tuning you might get away with it at 11:1 (i wouldnt advise that)
3. moderate performance cam
4. moderate performance carb
5. lockup converter (requires major mods) or get a 4speed. old school 727 with torq converter lose a couple mpg vs manual trans