Normal MPG from 400 SBC

[SunTzu]

Hi all,

I have a 71 C-10 SWB Fleetside with a 400 SBC to TH400, 12 bolt 4.11 rear with Detroit Locker. My speedo isn't hooked up but I running at 3000 rpm I am doing about 50-55 mph. I took a road trip through some state hwys keeping the rpms at about 3000 rpm. During the trip I averaged about 7.2 MPG. Is this normal? seems a bit low to me. I had planned on putting in an overdrive transmission and taller gears to get better hwy rpms but is the engine running rich? I know this is hard to diagnose over the internet. Some details. engine was transplanted from a 75 Chevelle or Impala, has Edelbrock 650 cfm carb and Performer Intake, Hedman elite headers, dunno about the internals. I live in Colorado, dunno if the carb is set for High Altitude or not. The tires on now are 255/70R15. The pictures of the engine are just after I got the truck, still has a Nitrous system in place, I have since removed the system. Pictures are all I have of the engine. They are probably not worth anything in this case.

Any input is appreciated, thanks.

Rob

Pics.