Clean look under that hood. Nice. Your mileage is about what I got on the highway in my truck, right at 20 MPG.....but if I decided to go much above 55, it dropped off.
Well mine was 20 mpg in mainly city driving, I haven't checked highway driving yet. I'm figuring that will be better yet. But I suppose the aerodynamics and weight of the truck versus the Camaro make a difference. 55mph makes sense, that was the national speed limit then and the gearing and tire size would have been designed to make peak efficiency around that speed. It's 70mph in Illinois now, so the 2.56:1 rear ratio (which they used in the smaller V8s with TH350 in '80 & '81 too) that was used on the last year of the 250 in '79 (which switched to the 292 SD head & intake/exhaust too) would be more efficient at the modern highway speed.
I read an interesting series of articles on the "deadly sins" of GM on the cars that lead to its decline. I think it was the Vega article where the author described the super wide range 3spd manual (3.50 1st, 1.89:1 2nd) as an overdrive 5spd manual with 2nd and 4th gear missing. That kind of makes sense from my experience with it, as first gear gets you across the intersection, but it bogs a bit if shifted to the 1.00:1 ratio before 40mph. With the 2.73:1 high ratio in the rear end, the overall drive ratios are similar the T5 in 1st (with 3.42:1 rear ratio), while the third gear falls somewhere between the 4th & 5th OD gears. So my seat of the pants experience kind of agrees with that author.
