Let's see what you guys have to say. Right now in my 80 Malibu wagon I am getting about 12-11mpg, all city. Here's the setup;
-350, ported 462 heads, 9.2:1CR
-Edelbrock RPM Intake
-Holley 650 Vac Sec, 66's in front, stock plate on back, purple secondary spring, 6.5 power Valve
-214/224 Hydraulic cam
-Turbo 350 trans and 3000 stall converter
-2.42 rear gears
-Car weighs about 3700lbs with me in it

Now by knows means do I think I should be getting 20mpg, but I think 14-15 is doable. Right now I am tuning with a narrow band heated O2 sensor hooked to a multimeter. Everthing seems pretty good but I have noticed a few things;

Car idles at about 0.880V, really seems to like that, idles about 700rpm. If I try and lean it out to around 0.500 the motor starts to gallop. My idle screws seem really touchy. I can go from 0.1V on the meter, to 0.95V with a 10deg turn on the screws. Also my screws are only about 3/4 of a turn out. Any ideas?

I think my power valve is acting funny. I can't tell if it's opening or maybe it might have a small tear. My primary cirucit is tuned pretty lean, ~0.200V, I don't see any decrease in AFR when vacum drops below 6". I diconnected the secondairies to see exactly what was happening with the main ciruit power vavle.

Is there a chance my power mileage and extremely sensitive idle mixture could be attributed to a leaking power valve? I will try a different one a see if it makes a difference, any suggestions? Car pulls 14" at idle. Also is there any way to tune the idle transfer circuit? Mine is too rich.
I think 14-15 mpg is doable especially with the 2.42 gears. I barley have to touch the gas and the car seems to cruise right along. So little that the car seems to cruise on the idle transfer circuit and not the main. Even on the highway. Seems kind of wierd I am getting poor mileage.

Thanks for any help
Steve

Heres your problem "3000 stall converter" that with the 2.42 gears are killing the effeciency of the engine. 12mpg is pretty damn good for a 3k stall.

I was getting 16mpg, with the exact same parts on a 305 with 305HO heads. Intake, Cam, Carb setup almost the exact same, headers, exhaust, trans, everything the same. The 350 does have about 100hp on the old 305. It just seems weird to me, because the new 350 I just have to feather the gas and the car has no problem maintaining speed. The 305 I had to use the throttle alot more. Just seems to me that the more throttle the more gas, the worse mileage. Now obviously 350 is bigger and gonna use more gas at the same rpm and load.

Also the converter is setup real tight. Has no problem at 2000rpm down the freeway. Now for sure I do agree the converter is definelty not ideal for mileage.

Thanks for any help
Steve