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Canadian Poncho Homepage -> Canadian Poncho -> Hillar's General 65-70 Full Size Forum -> Gas Mileage with a Big Block
Post Info TOPIC: Gas Mileage with a Big Block
66 Grande guy


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Gas Mileage with a Big Block
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OK maybe I'm bragging or maybe I just don't know how to do conversions but in a recent trip to Calgary and back from my home (about 6 hours each way) with the big yellow barge I checked my fuel mileage as the tank seemed to be going down more slowly than I expected.

Now, this car has a bone stock and fairly mild L35 (402 cid now though) with the the original quadrajet and the optional duel exhaust.  The only engine mod is the Pertronix in the original distributor.  The transmission is a TH700r4 and it runs through the original 3:31 open rear( with 60 series TA radials for a pretty much original tire height) The engine is running a power steering pump and the AC  compressor although it was not engaged. I had checked the speedo against a GPS unit and it was pretty much spot on. For a change I decided to run mostly in the fast lane on Highway 2 which means you've got to go in the range of 120 to 130 KPH and even then you will get passed frequently. According to the speedo I was between 70 and 85 the whole way with the engine running at about 2300 to 2500 rpm with plenty of power left. I don't think i even opened the 4 barrels the whole trip.

Once I hit a gas station after that run I topped up and ran the numbers using imperial gallons as that's what I grew up with.  It worked out to 18.8 mpg. That may not be great by todays standards but I was pretty happy with it. I decided to do 100 to 105 for the rest of the way home and checked it again and I got well into the 20's.

I've heard lots of stories about big blocks being horrible on fuel but this thing seems to be very livable as far as fuel goes.

Is this reasonable? Have any of you guy had happy mileage experiences with a big block?



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ken from northern Alberta

38 Willys pickup electric

39 Buick (327 with 700 r4)

66 Beaumont 4 door hardtop

69 Chevy CST pickup

1976 GMC 23'  motorhome

1994 Impala SS 

1968 Citroen Fourgonnette (Yeah Carl!)
427carl


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 Have any of you guy had happy mileage experiences with a big block?

         My old car travelled 1185 miles one way from New Brunswick in 2006  

         Travelling at 70 miles per hour it  "averaged" 16.8

         468 BB with headers,wild cam, and Holley,  and 350 turbo and 2:73's



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MoboMac


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Keeping a constant throttle....AND staying out of the secondaries......along with your overdrive....are ALL contributing to good fuel mileage...

Try the same run...on and off the throttle...and WOT........you will see a rapid decline.....With a big cube engine...it's easier to get lousy gas mileage...



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seventy2plus2


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When I do my long trips I keep track of mileage and fuel consumption.

For comparison sake, when I took the 454 Laurentian on a 3500 mile trip to POCI in Kansas in 2014, I averaged 17.75 mpg (Imperial Gallons) and that's cruising easily at 80 mph for 99 percent of the way.  The car did have cruise control in it.

This summer, I took my LS6 454 Parisienne 4 speed on a 3300 mile trip POCI in Iowa, and averaged 15.9 mpg.  I did keep my speed down to about 65 or 70 mph.

Your 18.8 mpg is a little higher than I'd expect from a big block, but not out of this world.

Conversion factor for fuel is 4.546 litres to 1 Imperial Gallon.  



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66 Grande guy


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Thats what I used.  Maybe I'm in the ballpark.



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ken from northern Alberta

38 Willys pickup electric

39 Buick (327 with 700 r4)

66 Beaumont 4 door hardtop

69 Chevy CST pickup

1976 GMC 23'  motorhome

1994 Impala SS 

1968 Citroen Fourgonnette (Yeah Carl!)
4SPEED427


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In the 80's, my daily driver (year round) was a 67 Grande Parisienne wagon 396 TH400, fairly loaded car including A/C. Pretty heavy car. It had a 3.07 posi and was not bad on fuel but not great.

During the time I had it, I parted out a 69 Grande Parisienne 427 car that had a 2.56 posi in it. I swapped that into the wagon and installed a later model Quadrajet on the advice of one of my co-workers. He showed me how to screw down the power valve on the Q-jet and although most people don't believe me ( and I really don't care!), that car would pull down mid 20's on a highway trip. I still have the trip diary for a week long auto wrecking run we took to Montana with that car with the fuel fills all documented. The average for the entire trip was a bit over 23mpg. Pretty impressive I thought for a heavy 396 car with A/C, no lockup converter or overdrive, laden with car parts on the way home and we were not obeying all speed limits along the way.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

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68beaumont


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Had a 66 Caprice 2 dr from 1980 to 1990, had 396(325 hp), TH400 and a 2.73 axle, would get 18 to 20mpg highway, always thought it was a good all around powertrain.



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goushdds


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The 396 in my Beaumont is consistently the same or better on fuel than the 283 in my Parisienne. But that is most likely because secondaries are open most the time in the Parisienne.

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davepl


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I drove Regina-Ottawa and back with a 396 in my 2+2. I got under 10mpg going there with a Holley 850 double pumper... the bumpers even got a rainbow hue to them from unburned fuel. Then I put a Q-jet on in Ottawa and managed low to mid 20s the whole way back with cruise control.

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66 Grande guy


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Yup. The Q jet will get you mileage and quite bit of power while the Holley may as well be called the flushmaster as its like flushing as toilet every time you hit the gas. Cant beat it for go though.



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ken from northern Alberta

38 Willys pickup electric

39 Buick (327 with 700 r4)

66 Beaumont 4 door hardtop

69 Chevy CST pickup

1976 GMC 23'  motorhome

1994 Impala SS 

1968 Citroen Fourgonnette (Yeah Carl!)
cdnpont


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I'll have no trouble getting 10 out of my new 496, right?

 

 



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