Between my 360 vs the 5.9, both stock long blocks, the LA had better mileage. Why? I don’ t know for sure. I think on paper, the Magnum has all the marbles. But it didn’t pan out that way. Your results may vary.
My LA was a ‘79 mill. Added on to it was;
A ‘72 trap door air cleaner w/a K&N filter
OE ‘79 cast iron intake
625 Federal Mougal AFB
JY distributor triggered by a MSD 6 and backed by a MP Chrome box. Because MSD stands for “May Suddenly Fail” in which they did for me, constantly.
2-1/4 H piped dual exhaust with twin catalytic converter’s (that was the law) and thrush mufflers.
A 904 w/the MP shift improver kit, 2.76 gears riding on 235/60/15’s. The car was a ‘79 Magnum. Best gas mileage was 20 mpg’s Hwy.
Run as much initial as you can, limit timing to approximately 34/36*’s, open up your plug gaps to .050 unless it misfires, then close them down .005 until it runs right, tune tune that carb!
I find the Magnum a little more thirsty. But power is much better! IMO, I think it is the cam specs.
IMO, your use of a 318 cid engine and the overdrive, in a lighter car, I don’t have a reason as to why 22 & better mpg’s can not be seen. I’m sure elevation has a role in this. As I live on an island, it wedge shaped maxes out at approximately 400 or so feet. At best. So I looked it up for ha-ha’s. 400 feet!
Highest elevation on long island - Google Search
