Gas mileage of older Cadillac -- including 331 OHV V8. Explaining a mystery.

[Jeff Rosansky CLC #28373]

Christopher is correct, timing.
We haven't really checked the mileage on the 55. However it has gotten better since we replaced the advance. We went 1000 miles with a bad vac advance. Now that we replaced it it is much peppier. Take the science out of it and just think about how much pedal you need to maintain speed. Vac advance means more power (you can feel it). More power means you have to push the pedal less for any given speed especially on a hill.
Jeff
John, we typed over each other but saying the same thing.

[wrench]

I agree with Ken's description of the methodology.

There is a lot of room for error just in the old odometer and looking at a milepost and then driving and you need to get the volume of gas from the same pump over multiple test runs and do an average and all that jive...

Now with GPS for speed and a straight flat road course and some sort of digital flow meter you could eliminate a lot of the slop, but what would be the point of comparing a scientific value to a 'real world' value?

Sometimes I am amused by the lengths people go to squeeze a tiny fraction out of something.

its a form of OCD like building a 100 point car.

I had the opportunity to say to a buddy of mine yesterday that perfection is a goal, not a state of being.

["Cadillac Kid" Greg Surfas 15364]

Jim
What I have been told is "there is no perfection this side of the grave"
Greg Surfas

[wrench]

i]there is no perfection this side of the grave[/i]"
Greg Surfas

Yes, I have heard that one too.

Thx

[Bob Schuman]

The biggest factor in gas mileage is the air gap. The more you can keep a large air gap between the accelerator pedal and the carpet, the better your gas mileage. Quite often easier said than done, though.

[jdemerson]

Update:
    On Saturday I drove to the Hemmings Concours at Lake George, NY in the Cadillac. Total driving time, round trip, was around 3 1/4 hours. All at highway speeds between 45 mph and 58 mph.  I checked mileage very carefully and it was 15.87 MPG.  I'm VERY happy with that. Of course the mileage in stop-and-go driving around town is MUCH lower. But installing the rebuilt vacuum advance on the distributor has made a dramatic improvement.

John Emerson

[5390john]

I took my first extended drive with my '55 De Ville this weekend.  Roughly 220 miles of about 55 miles per hour. I think I got 15 - 16 MPG. This is a fresh restoration, new radials, 3.07 rear end, premium with ethanol, pertronix ignition.
Does this sound about right?
John Adams