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Discussion Starter #1
Hi folks,

I've been having a bit of a discussion with exlimey over some tea and scones regarding the MPG's in our 250 CI straight 6 engines.

Exlimey is running with a 250 mated to a 2-speed Powerglide, and gets around 14 MPG.

I am running with a 250 3-speed manual and seem to be getting around 22 MPG. I don't have a tach in the '67 but I'm guessing it's around 3500 RPM at 65 MPH. That's just from counting. :D

Any thoughts on the gear ratios between the two setups? I'm thinking he's pushing 4000 RPM at 65 MPH (not that he can go that fast in the UP of Meechigan). Me thinks he should be getting better mileage with the 250 6-cyl - but maybe it's stop and go cruisin' up nord. Brrrrr! :devil:

Thanks for your thoughts mates.

Cheers, Tim
 

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Me thinks he should be getting better mileage with the 250 6-cyl - but maybe it's stop and go cruisin' up nord. Brrrrr! :devil:
No stop n go for me, 28 miles to work one-way, 2 stop signs and 2 traffic lights for the whole 28 miles! I just need to take it a little easier getting up to speed. :yes: :no:
 

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First off the 3 speed car will get better milage getting up to speed because you need less throttle because you have better gear multiplication thru first gear. Also, manual transmission cars get better fuel milege. They take less power to turn, and have no converter to slip, so even with the exact same rear gears and tire sizes, the 3 speed car will be turning less rpm at the same speed. I'm not sure about the first gen cars, but the 3rd gen cars, both the 3 speed manual and powerglide 6 cylinder cars came with 3.08 gears. I image the first gens cars are pretty similiar.
 

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I'm thinking he's pushing 4000 RPM at 65 MPH
The average 6 cyl/Glide car would have 3.08's in the rear, which would put him at about 95 mph at 4000 rpm..maybe you need to rethink this?
The 3 spd. manual will have the same 1:1 high gear ratio as the auto, but will be far more efficient, and therefore get greater mileage.
My 69 with 34,000 miles on the odometer, had a 230/3 spd. combo with 3.31 gears--trying to drive as smoothly and economically as possibly, I was able to get 19 mpg out of it. I hear people tell stories of how they got great mileage out of their 6's, but 8 out of 10 guys haven't got a clue how to even compute their gas mileage!
Go back and look at the road tests in 60's magazines...not many of them got over 20 mpg unless it was being driven for a Mobil Economy Run, which most of you have probably never heard about.
I drove a fully loaded 72 Caprice luxury liner with a 400" from L.A. to Illinois, and got 20-21 mpg, which completely threw me. I did this with my grandfather who checked his mileage EVERY tank in EVERY car he ever owned--and it was for real!
 

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Mpg

The PG car sounds about right. Your car should not be turning 3500 rpm @ 65 mph and getting 22 mpg.
Lot of things to consider here. How tall are your tires? If your car is turning that kind of rpm, it would seem to have more gear than a 3:08. On the other hand, if that is correct, you should be getting less than average mpg. If your getting 22 mpg, you must be coming down off the mountain.
As stated above, the 3 spd will get better mpg than the PG but it was very rare to get above 20 mpg, also as stated above.

It really is all about your foot on the gas. Believe it or not but some drivers used to take a car like yours and push the clutch in to coast every chance they got. This was a lot of work but it did increase mileage. I used to love to downshift to 2nd and let the clutch out coming up to a stop. When in fact the person pushing in the clutch and coasting to a stop, using the brake, would get better mpg.
 

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I saw 22+ with my stock rebuilt and well tuned 194/pglide/3.08s. I would cruise at about 55-60
My wore out 250 swap was getting about 17/18 mpg
 

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Discussion Starter #7
The tyres (kudos to exlimey) are P185/75/R14 ... similar to the originals, except they are radials.

I don't know the actual math yet, but I know I am getting 20+ MPG. I also don't know the RPM, since my grannymobile doesn't have a tach. All I know is that it is spinning lower than the '63 with the PG tranny. :eek:

More info to follow eventually. :D

Cheers, Tim

The PG car sounds about right. Your car should not be turning 3500 rpm @ 65 mph and getting 22 mpg.
Lot of things to consider here. How tall are your tires? If your car is turning that kind of rpm, it would seem to have more gear than a 3:08. On the other hand, if that is correct, you should be getting less than average mpg. If your getting 22 mpg, you must be coming down off the mountain.
As stated above, the 3 spd will get better mpg than the PG but it was very rare to get above 20 mpg, also as stated above.
 

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I have a 194/4bbl with a 350 Turbo trans & I believe i'm getting around 18-20 on the fwy 14-16 in town. I like the "kitted" automatic trans & leadfooting it at times is fun......:D.

BTW, What are scones ????
 

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I dont think a stock 6 can ever pull past 4k...

My 250 and pg with 3.36 gears was around 15-17 mpg.
 

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I think you should recheck your MPG.

I have owned several L6 cars over the years with various transmission/rear gear combinations. None ever broke into the 20 MPG range.

The overdrive will help, but don't be expecting too much.
 

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BTW, What are scones ????
English food is notoriously bad (I'm so glad my parents learned to cook better when they lived in Belgium) Anyway, a scone is like a less-sweet, stale muffin. :D And the tea is hot, with milk. :yes:

:puke:
That's why I'm an "Ex" :D
 

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Discussion Starter #12
Actually, even worse, it was a "traffic scone". :puke:

Oh yeah, and the mileage on the last tank, which I just filled up, was 22.8 MPG. Not a joke.

English food is notoriously bad (I'm so glad my parents learned to cook better when they lived in Belgium) Anyway, a scone is like a less-sweet, stale muffin. :D And the tea is hot, with milk. :yes:

:puke:
That's why I'm an "Ex" :D
 

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I don't know the actual math yet, but I know I am getting 20+ MPG
Oh yeah, and the mileage on the last tank, which I just filled up, was 22.8 MPG. Not a joke
Ever had the speedo checked for accuracy? Drive past one of the radar speed check trailers and see how far it's off. My Honda was off almost 3 mph when I bought it new--I got 27-30 mpg until I added a little taller tire. The speedo is still off about 1 mph, but my mileage dropped to 25-27 since it reads closer to where it should. If you drove the car extremely easy and used every mileage trick in the book during every drive, I could believe 22, but in normal everyday driving, I don't think so.
AAA used to do those speedo checks once in awhile for free.
 

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Oddly enough an over geared car will get poor milage too. I've always found 308 to be the tallest gear I wanted to use for combined highway and city driving. The PG's are not good city drivers with a tall gears, and the direct lock of the manual will hands down beat any auto for milage, by at least 3-5 mpg.
 

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Discussion Starter #15 (Edited)
We checked the speedo with the GPS on the way back from SC..... it's spot on. :yes:

After doing a tune-up, changed the fuel filter, cleaned/adjusted the carb (which was rebuilt at some point), the mileage went up from 19 to 22+. I'm not yanking your chain here - and I'm just as surprised as you are.

Cheers, Tim


Ever had the speedo checked for accuracy? Drive past one of the radar speed check trailers and see how far it's off. My Honda was off almost 3 mph when I bought it new--I got 27-30 mpg until I added a little taller tire.
 

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We checked the speedo with the GPS on the way back from SC..... it's spot on. :yes:

After doing a tune-up, changed the fuel filter, cleaned/adjusted the carb (which was rebuilt at some point), the mileage went up from 19 to 22+. I'm not yanking your chain here - and I'm just as surprised as you are.

Cheers, Tim
It's not calibrated for kilometers is it? :D
 
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