Which carb is best for MPG?

[rich ullsmith]

Greeting
                My daily driver is a 62 GMC Suburban. 350+ 030, Its pretty fresh, RV cam, Edelbrock AFB and manifold, HEI 10 initial, 36 total, ported vacuum, 9-1 comp., 700r4, 3.25, or close to it, rear, and is 1900 rpm @55 mph. This beast is heavy, 4500 lbs., I do not tow more than 700-800 lbs, infrequently. The carb and timing are close but can't do better than 11MPG.  This has to change.

I have a 283+030 in the works, stock cam, 9-1 comp.,and am going Q-jet. I have 3 solid, untouched cores;
7043212, small venturi;  17056512, and 17084231. Which carb is best for me? And why.  I'm a geezer so I'm light on the gas, never over 60-65. I want maximum MPG, that's what I'm shooting for.

Also, if someone has some good MPG ideas, I'd like to hear em'. The new block is still in pieces, so I'm flexible on that.  Thanks for your help, it looks like a fun site.       Rich U.

[Cliff Ruggles]

I'd use the newest carbureter, assuming the 17084231 is a truck unit and not a computer controlled carb?  I didnt go to the shop to research the number. 

The later carburetors have an APT system, and single main airbleed design.  They are very efficient and easy to tune. 

The Edelbrock AFB clones are an obsolete design.  The AFB was canned in 1967 as it would not pass every tightening emission standards.  The only thing good about them, is that they are simple and decent parts support for them. 

You will find the switch to a Q-jet will improve fuel economy tremendously.  A recent customer just reported getting 18.9mpgs' from his 455 cid powered Pontiac Firebird making over 500hp.

I've owned two Chevy Impala's that nailed down mid-20mpg's on the highway using Q-jets.  One was a 1967 SS with a stout 327 engine backed by a 4L60 trans and 3.31 gears.

We have everything you would need to build and tune the q-jet, and set it up for modern fuel, etc.....Cliff

[rich ullsmith]

Thank you for the post.  The carb has no electrics, so I think I'm good.  I wonder what the RV cam costs me in MPG?, I should get the specs so I know what I'm dealing with.

In fact, I'm going to change just the manifold and carb and see what baseline difference is.   In my area there is a small army of similar type rigs (AFB) that have the same MPG problem. This would be good news for them.
Terrific book, need to get another.  Thanks again, Rich U.

[Cliff Ruggles]

AFB style carburetors were canned in the late 60's as they would not pass emission standards at that time even with factory experts working with them. 

The Q-jet replaced them, and is superior at fuel efficiency in comparison.

The Edelbrock AFB clones are among the very worst carburetors out there.  They are extremely popular because they are dirt cheap, and almost completely idiot proof.  They failed (miserably) every test I've ever done with them here, street, dyno, and at the drag strip.

Not only will a well prepared Q-jet outrun them in all areas, they will get a LOT better fuel economy along the way.......FWIW.....Cliff