will this combo kill my MPG?

[caferacerx]

I have been reading how air gap type manifolds kill your fuel mileage
so now I am stuck, I would like better power AND MPG (greedy I know)
current engine is a 318-3 2bbl low comp truck motor
I also have a 1967 LA318 (factory rated 9.2 comp with closed chamber 273 heads) I was planing on installing a pair of MAGNUM heads (junk yard take off) with a crosswind intake (Chinese air gap copy) Eddy 600 carb and Comp 268H cam (454 lift 218 @ 50 duration)
my other option is
1: rebuild the original 273 heads
2: get a pair of junk yard 302 heads
and use my LD4B intake
or just keep my trusty low comp 2 bbl truck motor

power is good, but fuel economy is better
(at least with the price of gas today)
the car is a 66 barracuda, 4 speed, 2:94 rear, 14" tires,
not interested in going fast, just cruise around for fun

 

[RustyRatRod]

Use the 318 Eddy performer and a Thermoquad. Power and mileage.

 

[hemitheus]

Drop the air gap for a conventional performance intake. Dual plane is more street friendly. Single plane for more strip use.

 

[Abodybomber]

You live in Philly,gets nasty cold. You need the heat riser port,and the Performer . Cam,a great choice.The lack of heat riser(under carb)heat,is what kills cold drivability,and m.p.g.'s. A Thermoquad ,in that weather,would rock. Rumblefish,lives in N.Y.He might know.

 

[340 8BBL]

Use the 318 Eddy performer and a Thermoquad. Power and mileage.

what he said,and ill add: an isky 256 super cam,or the 256/262 dual pattern.both are rv/torque cams with mpg in mind.

 

[caferacerx]

Drop the air gap for a conventional performance intake. Dual plane is more street friendly. Single plane for more strip use.

the air gap / crosswind is a dual plane, and is the only one I have with MAGNUM bolt pattern

the 268H cam came with the 67 318 motor,

dont have a thermoquad, just an Eddy 600 and a 600 Holly off of a 1972 440 motor (came stock that year)

I am trying to use what I have, this is a very low budget deal, no money to spare,