[mnunn454]

Originally Posted by mnunn454

I agree.

Before changing ring and pinions, or engines, or trannys, I'd start with the carb and HEI.

Regarding carb's:

A) Visit a chassis dyno and have them jet it for economy when cruising at highway speeds (NOT W.O.T. HP). Or,
B) Try carb tuning yourself by changing carb jets or needles and watching the plug colors (An O2 sensor in the exhaust pipe is a big plus in this regard). Or,
C) Replace the carb with a rebuilt Q-jet or Edelbrock #1405 or similar.

I'd think 12-13MPG isn't an unreasonable expectation for a V8/373 geared truck (once the air/fuel ratio is adjusted properly). The 50% reduction in fuel consumption will repay any hardware investment costs in short order.

To get 16MPG or more, you're likely going to have to drop to a 3.08 R&P or install an overdrive tranny (manual or automatic, you choose).

Upgrading to EFI and an overdrive tranny should net you over 18, but it's a lot of work and maybe cost to convert.

of course, all this assumes you don't have a gas guzzling cam, really low compression or the emergency brakes frozen up ('Been there. Done that. Got the T-shirt).

I just posted the response below on another thread. Pasted it here as well because I think it addresses this problem too.

Here's the reasoning behind my belief that greatly improved mileage can be had with a good carb tune (not just a simpe rebuild).

It's a Chevy High Performance article from a year or so ago called "Old school meets new school". It's on-line at
http://www.chevyhiperformance.com/te...age/index.html

In short, using some tech tools, this guy has a 500+ HP SBC and adjusted his Mighty Demon carb's idle air speed and high speed air bleeds to increase the operating range (RPM and load) of the idle circuit and delay the onset of the primary's main metering circuit. Result was smoother operation and 21 MPG on the trip home following a drag racing outing (granted he has an AOD tranny).

It's a technical article, so grab a cup of coffee before you sit down to read it. I think once you read it you'll agree that a lot can be done to improve mileage as long as you can see what your air/fuel ratio's doing.