Right, but 18/22 mpg as printed in that 1981 ad is wildly optimistic on account of the test protocol in use at that time. See here for less-unrealistic numbers (because they've been adjusted in accord with the current protocol).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yes, I understand. I'm old enough to remember going car shaping with my folks and hearing my dad say "there's no way it can get that kind of mpg's"

In less you really love the slant 6, the 318 would probably do equivalent,,,, With same equipment?

I know the 5.2L Magnum will come close... carbed stock 318 would be a bit less...

As much as I love the slant six, unless you are running a very lightweight truck or van and don't tow ever, a 318 will likely get equal or better MPG in a truck/van. The best I ever achieved was about 16-18 MPG in my brorther's 1983 Dodge shorty van with a 225/904 that was freshly tuned up with some modifications (Super Six, big valve head, hot coil,etc...) driving a steady 60-65 MPH on the flat highway. 13-15 MPG is more realistic in a slant powered automatic truck or van.

Mileage can be fairly good with the correct setup and build. Your rear gears will affect mileage a lot as well as seat of the pants feel. My truck with the 2.76 road gears got nearly 22MPG on a trip to the race at Bristol last year. That is with an automatic without lock up.This was checked off the GPS so the mileage is correct. I have an 8 3/4 rear so I can easily swap gears. I run 3.55 normally and for towing my race car. With the 3.55's running local I can get 16-17 MPG if I drive for mileage. If I drive like I want to I get in the 13-14 range. My complete build is here about half way down the page.
http://slantsix.org/forum/viewtopic.php ... &start=150

As a reference I have a 2013 Chevy Van with a new modern engine and overdrive transmission. I just made a 450 mile trip yesterday and on 2 tanks of gas the best I got was 13.9 and that was all highway driving. Granted it has more weight and more power than most slant 6 trucks, but that mileage is not great in my opinion either.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6