Peeeot.  I’ll suggest just adding some initial advance in increments to what you already have.  There’s the chance the damper has slipped or simply isn’t reading correctly against the timing pointer.  If you see some gains in the mpg numbers doing this, then it would be worth the effort in verifying that TDC on the damper is indeed correct.  When doing changes for fuel mileage gains, it is recommended to run at least three tanks of fuel for each change so that any detrimental variables can be buffered out of the numbers when averaging.
 
I’ll add that a retarded camshaft can also be a hindrance to the fuel economy but your compression readings are high enough to have that as a minor player.  Might be worth checking the cam timing when all other areas to look at are exhausted though.

Lorena, Texas (South of Waco)

I have to use California blended gas which is different the the other 49 states, God only knows what it is but I'm sure it's crap LOL. I've made 4 long distance trips of 280 miles round trip to visit the grand kids and averaged 17-18 mpg in the Ranchero. 292, E4 cam, 390cfm Holley, 3.89 gears, three speed overdrive trans, 215x70x14 radials. I know comparing this to a 312 with auto is like apples and oranges but I think the your 312 should be doing better then what it's getting.

I haven't experienced any issues since ethanol became a big deal.  No decrease in mileage, no decrease in performance, no rubber or metal parts deteriorating prematurely.

I did tune my carb with an O2 sensor.  I even erred on the rich side, as indicated by the gauge, and my plugs are always white. .  If I hold one next to a brand new plug, the new one is brighter, but it's not a whole lot of difference.  My thought, given the color of your plugs, maybe you are too rich for ethanol blended fuels.

While I haven't experienced problems with ethanol, it may still be worth a shot for you to experiment with that.  Premium fuel is suppose to have less ethanol than the lower grades.  You could try a tank of premium.  But, that doesn't mean a whole lot, unless you can know that there is less or none, so you need an ethanol test kit.  That way you can test a sample of fuel to know the percentage of ethanol it contains, and therefore determine if there is any correlation between the percentage of ethanol and fuel mileage.  You can get ethanol test kits at places that sell lawn mowers, and yard equipment like that.



Lawrenceville, GA

I would look for a rear ratio in the high 2s,with a 312auto any thing in the 3s is to low geared. i have a 57 292 with 3,25 3spd standerd and it is to low geared,ys have great low ent torqe and with a auto trans need gearing in the 2s eith,i run a holley 4v 550 vacume seconds.

Greetings to all: I have found a fast and simple way to determine the alcohol percentage of gasoline. A good accurate glass 100ml graduated cylinder  and a good jar with a tight fitting lid is all that's needed. Fill the cylinder to 50ml and to that add 10ml of water. Pour this 60ml concoction into the jar and shake it for about 40 seconds or so. Pour this back in to the graduated cylinder and see how the 10ml of water "grew."  Probably will look like about 15ml which means it pulled out 5 ml of alcohol from the fuel indicating 10%.  Recently, samples from my local BP station here in Michigan showed 10% for regular, 6% for mid grade and 8% for premium.  I purged the gas pump hose first by pumping a couple gallons in my car, then pumped a gallon in a clean empty sample can. This method served well when burning auto fuel in aircraft approved (stc'd) for auto fuel. That is, before the days of alcohol in pump gas. This mileage discussion is very interesting as I consider it a quick indicator of vehicle health and efficiency. I rebuilt and made my 292 into a 1957 312 for my 64 F100 including a custom cam ground by Oregon Cam to 57 specs. So far I've had to advance the cam 4* and I'm getting 14 to 16 mpg.  The truck has a 3.5 rear gear and 3 speed overdrive. Next thing on the list is to dial in the 450cfm Quick Fuel carb with a wide band air fuel meter as the plugs are a bit on the dark side and the exhaust smells a bit rich also. Hope this helps, JEFF..........


64F100 57FAIRLANE500

Given your input, in your early posts:

All my calculations, using your data for rpm & tire size, tell me that your rear axle ratio is 3.70 to 1.
If you really had a 3.10 axle ratio, then at 3000 rpm you'd be traveling at near 84 mph.
This, I think, is really a big part of the problem.
With a 3.10 axle, at 70 mph, you'd be at 2500 rpm. A much better ratio.
Just some more food for thought. Hope it helps.
Jim

That is a great observation.  I have a slightly taller tire, 28", and a 3.70 and 70mph is right around 3000rpm.  Given how easy it is to swap 9" center sections, that could be the reason.



Lawrenceville, GA

I'm also running a 370 but with an AOD. It's great on take off but when in 4th the rpm is a little low for performance. It cruises just fine but a bit out of the power range. About 2600 at 65. The AOD is in need of adjustment of the shift points but I can't find anyone local that can handle it. Right now it upshifts to 4th at about 48. The rpm drops below 2000 and it barely will pull hills. At higher speeds it is better. I'm thinking of installing a 410 gear. That should bring the rpm up a bit. I am still running the stock 56 rearend but with a posi. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

You might be ok once you get that supercharged motor in there.



Lawrenceville, GA

Re rear end ratios:
Moonshadow
On my 32 Ford, I have a large flathead (290 CI), a Ford toploader four speed, then a Gear Vendors O/D behind the transmission.
The rear axle ratio is 4.11:1. Tires are 29" in diameter. The overdrive drops the final ratio to 3.21. 
The engine has a Potvin 425 cam with 245 degrees @ .050".
The engine has (2) 4 bbl teapots, linked together, not progressive.
On the road, car will exceed   21 mpg. I've often thought about going to a 3.78 ratio, but then would lose a bit of the  performance.
This is in a Tudor sedan that is shaped like a cardboard box going down the road.
IMHO, lower rpms mean better mileage.