Tlowe got 20+ MPG on a pretty mild 250 build with a 2 bbl in a Chevy II wagon. So a lot can be gained by tinkering.
I mentioned earlier in the thread that 1978 was the first year for EPA mileage listings and the '78 Camaro L6 was rated 18mpg in the city and 28mpg on the highway, with an average of 21mpg. I checked mine two years ago and it was about 16mpg with half the exhaust and no tuning in city driving. That's with a 3speed manual and 2.73:1 open rear end. Integrated-J-78 said he was able to get 23.5mpg on mostly highway. I think I'll get a highway route from a gas station going out to an ice cream shop and back to the same gas station again, and use that to measure best fuel economy along with a drive with the wife for a treat once a week.
I already have new plugs indexed and gapped to factory recommendation. So I'll clean up the HEI, add a new cap and rotor, and 8mm wires. Then put a timing tape on the balancer and reuse the 36 year old springs and see what the factory vacuum and centrifugal advance are at and have a baseline to work from. Then I can start playing with different advance combos and see how it changes. It will be an all summer job, but I probably can't afford a top end swap until next year anyway.
