Small block gas mileage DD magnum/LA ?

rustytoolss said
Looking to builds a stockish 5.2/318 for a DD. If I use a 5.2 magnum, it will use the stock roller cam. aftermarket intake and a small Edelbrock Thunder carb, and elecrtonic DIST. cast iron exhaust manifolds.
Or should I use a LA 318 (which I have 1986 truck engine) possibly small summit cam, 4 barrel intake, small AVS carb, electronic DIST, and cat iron exhaust manifolds.
Will have dual exhaust , and have a 42RH /A500 with stock converter. Rear gearing possibly 3.23.
So which combo should provide the better gas mileage ? I got the 318 for free...so I can walk away from it..if I choose to.

toolmanmike said
Probably not as high as 25 but close to 20 I would estimate .

5.9 Magnum, EQ heads with LA intake bolt pattern, Edelbrock dual plane, Edelbrock 1406, HEI with a .050 gap, NGK plugs, 1-5/8 long tubes, 214/224 Oregon cam, 42RH, 3.55 rear gears, synthetic lubes in engine and diff.
24-25 mpg on the hiway in OD and lockup at 75 mph.

18 initial, 34 total and 50 or so with vac advance.
Averaging 14.5 AFR.
Then I put a Holley 770 on and never checked the mpg after the change.