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Red Horse
Cochise

376 Posts

Posted - 22 Nov 2019 :  02:08:48 AM  Show Profile  Reply with Quote
When i fill up at the gas station in town I use 1.2 gallons to go 32 miles. If i fill up at my destination and return to the original starting point I use 2.2 gallons of gas or petrol for our Aussie friends, and the Brits. Granted I am in stop and go traffic on the return. Still seems to being excessive consumption to me. This is perplexing ,any ideas ?

Corncob2061
Crazy Horse

USA
645 Posts

Posted - 22 Nov 2019 :  09:46:28 AM  Show Profile  Reply with Quote
So your getting 25 mpg one way, and 13.6 mpg on the way back? Route out is highway driving, route back is city stop and go? Jay

Edited by - Corncob2061 on 22 Nov 2019 09:46:54 AM
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Blued and Painted
Chief PONTIAC

USA
3521 Posts

Posted - 22 Nov 2019 :  12:37:49 PM  Show Profile  Reply with Quote
U would have to use a graduated container to measure accurately. Even a couple degrees of tilt front to back or side to side of the vehicle can change the effective volume of the tank. An equal length cold start trip will use more fuel than a hot start trip. Also fuel expands or contracts a substantial amount with temperature change. Under ground fuel tank temps remain stable where the vehicle fuel tank temp varies. Too many variables.

Figure mileage after refilling an almost empty tank will be the most accurate. Then average the results over a few tanks.

This will be your bragging rights number.

Anything over 14 mpg would be excellent mileage and indicate a good state of tune.

I will now microwave some popcorn.



461/TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 22 Nov 2019 12:53:24 PM
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Red Horse
Cochise

376 Posts

Posted - 23 Nov 2019 :  12:48:10 AM  Show Profile  Reply with Quote
Same route used in both directions. Return route is about 3 miles in traffic.
I'll try the almost empty tank fill up and see what I have. This may take a week or so as I only drive the car a few days a week.
My speedometer is off 5 miles per hour. Hour does this effect my distance traveled. I've using a measured distance from my wife Madza 3, which is how I know the downtown to home mileage is 32 miles
And now I will retire to the sofa and a Bloody Mary.

Edited by - Red Horse on 23 Nov 2019 04:33:19 AM
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Red Horse
Cochise

376 Posts

Posted - 15 Feb 2020 :  12:10:46 AM  Show Profile  Reply with Quote
I've run a few tanks of fuel thru the engine, Mileage is 11 MPG. This is very poor for a car with a P350 engine and no mods. My 69 Marquis with the 429 4bbl got around 18/19 My 50 pontiac got about 18/19 also. The Packard got around 15 with 327 and 4bbl. 70 Chevy station wagon with 454 got around 18.
Even with todays lousy gas 11 seems to be low.
The only mods are 200/r4 trans. and Holley 4,
Any suggestions?
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Corncob2061
Crazy Horse

USA
645 Posts

Posted - 15 Feb 2020 :  8:28:47 PM  Show Profile  Reply with Quote
Are you getting full advance from vaccuum? 45-50 total? Ever taken a compression test on the 350? Any idea what jets and power valve are in the Holly? One would think it would do better than 11 with a 200r4. Jay

Edited by - Corncob2061 on 15 Feb 2020 8:40:30 PM
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Brian Baker
Mongo

USA
1086 Posts

Posted - 16 Feb 2020 :  12:13:21 AM  Show Profile  Reply with Quote
Where are you getting 11 MPG?

My math says 32 miles traveled and 1.2 gallons burned = 26.67 MPG.

32 miles traveled and 2.2 gallons burned = 14.55 MPG.

If any of the vintage Pontiacs I've owned in the last 35 years got better than 14 MPG I'd be ecstatic.

Will Rogers never met a liberal.
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Red Horse
Cochise

376 Posts

Posted - 16 Feb 2020 :  11:35:27 PM  Show Profile  Reply with Quote
I'm getting full advance, Dn't know what jets are in the carb . I do know it is a marine carb.. No external float adjustment. The power valve may be blown. Never did a compression check.
Mileage estimates are new data based on running 4 fill ups of around 10 gals each.

quote:
Originally posted by Corncob2061

Are you getting full advance from vaccuum? 45-50 total? Ever taken a compression test on the 350? Any idea what jets and power valve are in the Holly? One would think it would do better than 11 with a 200r4. Jay

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Corncob2061
Crazy Horse

USA
645 Posts

Posted - 17 Feb 2020 :  8:01:03 PM  Show Profile  Reply with Quote
It is not a blown power valve. The engine would run terrible. Hard to say if the power valve or jets are right for the engine. I am not sure how holley sets up their marine carbs. I would think there could be some milage from some carb tuning. That carb may not be real easy to tune though.

Is 11 with a mix of city driving? Ever checked the economy between two stations out on the open road too see what it is capable of on the open road for mpg? More or less checking to see were the fuel is going.

Is it starting right up after it is shut off for a short time?
Jay




Edited by - Corncob2061 on 17 Feb 2020 8:02:57 PM
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Red Horse
Cochise

376 Posts

Posted - 18 Feb 2020 :  01:05:11 AM  Show Profile  Reply with Quote
Well I figured out what the problem is, its a fuel leak. the only thing I hadn't checked, so L look under the car and there is fuel dripping fro the fuel pump. Can't tell whether its the fuel return or the fuel inlet fitting.
Funny thing I couldn't smell fuel lucky for me I didn't set the car on fire.
This fix will have to wait while I have more pressing to do's.
After the fuel problem is fixed I want to try tuning the carb. Something of which I have little experiance.
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p.rat
Two Feathers

USA
34 Posts

Posted - 22 Mar 2020 :  2:11:27 PM  Show Profile  Reply with Quote
As an aside to your speedometer/odometer inaccuracy, Tire Rack and other sites have calculators to help find your true mph and by doing the math, you can figure other data such as your tire's revolutions per mile. This may help you get an accurate mpg figure. May be worth a look once you have all else sorted out.
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