318 mpg

I finally checked the mpg in my desoto while driving to Carlsile. I was shocked that it was 26mpg! It’s a .030 over LA roller 318 with magnum heads, 3x2 9super7 carbs, a reground roller cam(not big only .436 lift) block hugger headers and 2.25” dials with x pipe. It’s an 833od with 323 gears.

My 87 Diplomat would get that but it depended on the speed I was running, 65 or less yep, 70+ not so much.

I have two 318 cars, the wideblock gets awesome mileage and the Cordoba was a gas pig UNTIL I replaced the exhaust. Was a single exhaust with manifolds and a cat- I put headers and 2 1/2 mandrel bent duals out the back, a little more power but WOW way better gas mileage!!!!

My 318 Poly got a maximum of 16mpg with 3.23 gears and 32" tall rear tires. That's with the carb leaned out, which means down jetted until it has lean surge then one jet number higher.

I replaced it with an '86 318 roller motor. I home ported the 302 heads, swapped in a 360 /5.9Mag camshaft, added the cast iron EGR 360 manifold, adapted the Poly's carb to it. So same carb not changed and same exhaust system with stock low perf manifolds piped back to the exact same exhaust system. This is a 100+ K engine. First tank was 22mpg! That's in a '64 D100 long sweptline.

That chamber is magic.

R.

Hi, Sorry I'm old, not that smart, and not up on things, what chamber ?

Cylinder headchamber.
'302' heads are known as swirl type heads and promote better combustion and burn.

I wish I could say I had the same experience with the '302' heads but both on my previous stock 318 rollercam engine with 302s and the current 11.3:1cr 360 with polished 302s in my daily driver produce the same 'lousy' mileage of around 11-12mpg.
But I still suspect the A518 and its '60s torque convertor behind both engines being the main culprit here.

The 302 headed roller cam 318's came with lockup A998's and 2.45 rear gears. Not an OD trans or high stall converters, or steep gears.