Small block gas mileage DD magnum/LA ?

MileHighDart said

I just did my first gas mileage test a few weeks ago.
'68 Dart, 5.9 Magnum, stock bottom end, edelbrock airgap, edelbrock 1406, Doug's headers, dual 2-1/2" exhaust. Stock mopar electronic ignition, A500/42RH trans, 3:23 gears, 225/60/15 tires.

Also, I'm at about 5300ft elevation.
Filled it up and drove to work all week (40 mile round trip), I'd say 3/4 highway driving using the overdrive as much as possible, 1/4 in town.
I got barely 15mpg out of it. Was hoping it would be a little better, but the 42RH is still the best thing I ever did to the car. Cruising rpm's on the highway is just way more comfortable than with the old 904. If I remember right 65mph is like 2200rpm with the overdrive and lockup on.

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I get around 13.5-14 MPG with my stock bottom end 5.9 with ported Edelbrock heads and custom-grind hyd roller, 904 trans with 2.94 gears in a 70 Duster. I'm in Fort Collins so similar elevation around 5000'. Have you leaned out the cruise circuit on the carb very much? I've picked up 3 MPG on a 360 across the board just from leaning out the cruise AFR from ~14.3:1 to 16:1. First thing I did after installing my wideband O2 sensor lol.

When I installed a Edelbrock 1406 on my truck's 360 (stock 1972 converted from 2-bbl) it had factory jets, I went down one size on the jets all around and tried different metering rods to lean it out until it had noticeable hesitation when opening the throttle, then went one step richer (while also keeping an eye on running temps). Runs great and gets.... wait for it.... 10 MPG :rofl:

Even tried one step richer than that to be safe and nothing changed except the gas mileage dropped to 9-ish. Ran a bit better when cold but that's not how they're supposed to be anyway.