Eight MPG?!

[Number21]

I've had my '73 for a few weeks now, at first I calculated almost 10mpg, then closer to 9, now I'm at about 8.5MPG. I know these things weren't built for mileage but come on! I used to have a C20 with a 454 that got better mileage than that!

My truck is a K20 with 350/350/NP205, 4.10 gears in the rear and 33" tires. I know the tires aren't helping either, but does 8.5mpg sound ridiculous to anyone else? The only reason I want a small block over a big block is to hopefully get double digits. I drive 95% on the highway at 55mph, which calculates out to about 2300 engine RPM. I checked the odometer with my GPS and it is right on, and this is with a canopy on the back.

I don't know much about the engine other than what I can see from the outside - it's not stock - has an Edelbrock 4bbl carb and intake, headers, and HEI ignition. It starts and idles great and seems to run fine. I plan on replacing the fan (it doesn't even have a clutch) with electric and synthetic oil in the drivetrain...but I don't feel like I should have to have that stuff to get better than 10mpg, am I wrong?! If I can't improve it much I will put in a big block instead. My tailpipes (dual exhaust) are only 1 7/8" ID, would it help if I put larger pipes on?

Also I have an open element air cleaner...I like how it looks, but is that killing the mileage? What does the stock air cleaner look like on a '73, it doesn't have a snorkel like the later models does it? The cap and plugs look ok to me but I'm going to change them anyway...