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post #1 of 9 (permalink) Old 06-06-2012, 09:14 AM Thread Starter
Hal
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Greetings Once Again, fellow Impalagins,

Since my question relates to "performance" this seemed like the right column to place it in. I would like opinions from any of you who have experience in tweaking your engines for better gas mileage.

My '63 Impala still has its original 283 V8 and Powerglide tranny, with just over 84,000 miles on each. Whether at idle or highway speeds, the motor sounds smooth and normal. Also, acceleration is good. My question is: Is the 15 to 18 mpg I get from this small block V8 considered normal? This range covers city driving to open road, including Interstate highways. One concern I have (since the carbuerator was rebuilt around the 70,000+ mark, I recently changed all spark plug wires and the plugs installed at the moment have no more than 10,000 miles on them) is whether the points and condenser in the distributor should be replaced, even though everything runs smooth and sounds normal. Though I'm sure these items were changed before, sometime during the history of this car, in the four and a half years I've owned her they have not been touched. Call it one of those situations where "if it ain't broke don't fix it."

I'll appreciate any and all advice. Thanks!

Les
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post #2 of 9 (permalink) Old 06-06-2012, 09:59 AM
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Yes it is. I figured you were complaining about the 12 to 9 miles per gallon most American V-8 autos get (a big block drops that down into the 11 to 6 miles per gallon range). To improve your mileage do what Chevrolet did. Replace the transmission with an overdrive. I would recommend a 200R4.

Big Dave
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post #3 of 9 (permalink) Old 06-06-2012, 03:07 PM
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I have a 65' and when I had a 283/powerglide in it with a 2 barrel carb, I was getting 18-20 mpg on the highway, so your numbers sound correct to me. I have since switched to a 327 with a 4 barrel carb, HEI and some other mods, and will be doing a 200-4r here shortly. Anything older than 1970 that gets better than 15mpg is great in my book!

-Nick

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post #4 of 9 (permalink) Old 06-07-2012, 11:58 PM Thread Starter
Hal
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Thank you gentlemen. I am relieved to hear that. For now I'll just leave "well enough" alone.

Once again you can color me GONE!

Les
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post #5 of 9 (permalink) Old 06-11-2012, 12:33 PM
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Quote:
Originally Posted by Big Dave View Post
Yes it is. I figured you were complaining about the 12 to 9 miles per gallon most American V-8 autos get (a big block drops that down into the 11 to 6 miles per gallon range). To improve your mileage do what Chevrolet did. Replace the transmission with an overdrive. I would recommend a 200R4.

Big Dave
This isn't right. Just putting in an overdrive may not help, depending on the rear gear ratio. As many of these cars has 3.08 rear gears, you can put in an overdrive, but you'll be driving in 3rd all the time to get enough RPM.

And I'm not sure where you get your figures from, but 6 to 11 miles per gallon isn't right (or 12 to 9). I have always got at least 18 with my vintage cars, usually more like 20.
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post #6 of 9 (permalink) Old 06-11-2012, 05:09 PM
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Probably because all of my 327's where actually displacing 331 with 11:1 pistons and solid cams, my 350's where all 355's and they made well over 400 horsepower even back in the old days of Sunoco 260 and American White 104 Octane gas. My big blocks all had 12.5 pop-up open chamber domes and huge cams with some of the wildest carbs Holley ever sold. I had a Phase III Baldwin-Motion Camaro RS-SS with a full deluxe interior and 4.88 rear gears with a Muncie four speed. It got 1.2 miles per gallon, powered by an L-88 427 with a tunnel ram and two fours but it was a fun car to drive.

My 454 Suburban gets 6 miles to the gallon whether I am towing a 7,000 pound trailer or empty; probably due to the 4.11 gears front and rear in a three quarter ton four wheel drive truck. (It dropped down to 4 mpg when I replaced the 454 with a 502). My '89 Caprice has a 513 horsepower 406 small block with 3.73 rear gears and a 700R4. It got 11 mpg if I kept my foot out of it. My 582 big block 1985 Impala can not get more than 3.2 mpg even with a 4L80e overdrive, but it has 4.56 rear gears. Worse than gas mileage is the number of tires it burns through in a month.

My new pick-up truck has the 5.3 LS-2 motor with a six speed overdrive tranny, 4.11 posi and gets 20.0 mpg last time I checked the gauge.

So from my perspective he is getting great mileage.

Big Dave
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post #7 of 9 (permalink) Old 06-18-2012, 02:41 PM
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Quote:
Originally Posted by 05snopro440 View Post
This isn't right. Just putting in an overdrive may not help, depending on the rear gear ratio. As many of these cars has 3.08 rear gears, you can put in an overdrive, but you'll be driving in 3rd all the time to get enough RPM.

And I'm not sure where you get your figures from, but 6 to 11 miles per gallon isn't right (or 12 to 9). I have always got at least 18 with my vintage cars, usually more like 20.
Colin, an OD tranny will ALWAYS help. Even if your rear gears aren't well suited for an overdrive tranny, you still get the advantage of a lower first gear, which does increase gas mileage when switching from a powerglide. I know what you are saying about having gears to put the OD gear in the zone, but the advantage of a 4 speed OD trans vs. the powerglide has advantages in first gear as well, not just 4th.
You could put in a OD tranny and never put it in 4th gear, and still get better mileage, as the 3rd gear's 1:1 ratio is the same as a final gear in any old non-OD tranny.

-Nick

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1965 Impala SS
6.2L LSX with 4L80E, 3.73 Gears, Disc Brakes, Air Ride
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post #8 of 9 (permalink) Old 06-19-2012, 10:55 AM
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Quote:
Originally Posted by nicke View Post
Colin, an OD tranny will ALWAYS help. Even if your rear gears aren't well suited for an overdrive tranny, you still get the advantage of a lower first gear, which does increase gas mileage when switching from a powerglide. I know what you are saying about having gears to put the OD gear in the zone, but the advantage of a 4 speed OD trans vs. the powerglide has advantages in first gear as well, not just 4th.
You could put in a OD tranny and never put it in 4th gear, and still get better mileage, as the 3rd gear's 1:1 ratio is the same as a final gear in any old non-OD tranny.

-Nick
While you're right, my comment was meant as a comparison to a 3-speed, not the powerglide. However, in either case my comments were based on 2 points: 1. Most people don't realize when they should or shouldn't drive in overdrive. If your car isn't geared for an overdrive, simply bolting one in won't help gas mileage, and you might as well just go with a 3-speed in that case. 2. It depends on the type of driving you are doing. If you're in the city, going from light to light, you may notice a difference in overall mileage with the lower gear for starting out. If you're doing lots of highway driving though, it will make no appreciable difference in your overall mileage compared to driving in the right gear (and ideal engine RPM) at highway speed.

As most people don't realize that just bolting in an overdrive may not instantly increase their mileage (and can make it worse if the engine is going to be lugging), a 3-speed is a better choice for some people.
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post #9 of 9 (permalink) Old 06-19-2012, 11:11 AM
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Quote:
Originally Posted by 05snopro440 View Post
While you're right, my comment was meant as a comparison to a 3-speed, not the powerglide. However, in either case my comments were based on 2 points: 1. Most people don't realize when they should or shouldn't drive in overdrive. If your car isn't geared for an overdrive, simply bolting one in won't help gas mileage, and you might as well just go with a 3-speed in that case. 2. It depends on the type of driving you are doing. If you're in the city, going from light to light, you may notice a difference in overall mileage with the lower gear for starting out. If you're doing lots of highway driving though, it will make no appreciable difference in your overall mileage compared to driving in the right gear (and ideal engine RPM) at highway speed.

As most people don't realize that just bolting in an overdrive may not instantly increase their mileage (and can make it worse if the engine is going to be lugging), a 3-speed is a better choice for some people.
I totally agree with your points.
-Nick

OCD Customs
My Wheels
Classic Nation car pictures.

1965 Impala SS
6.2L LSX with 4L80E, 3.73 Gears, Disc Brakes, Air Ride
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