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Old 04-02-2013, 04:35 PM
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mpg question

on a car equipped with a double pumper carb settup

is it better to drive around at say 2000rpm in third gear at 30mph with the gas pedal pressed down 25% of the way

or to drive around at 1200 rpm in 4th gear at 30 mph with the gas pedal pressed down 50% of the way ?

in which scenario would I achieve the best mpg's

it's always recommended to stay in as high a gear as possible for fuel economy, but does that still apply if you're dogging it ?

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Old 04-02-2013, 07:21 PM
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I am no expert but the lower gear is going to use less gass in my opinion as it is not dumping fuel it can't burn hence the bucking and bogging ! May be wrong but believe that's better for your motor as well !
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Old 04-02-2013, 07:26 PM
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I agree. By the same token, a big block pulling a heavy load will get better mileage than a small block pulling the same load, or a 4 bbl getting better mileage than a 2 bbl under some circumstances.
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Old 04-02-2013, 10:49 PM
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the cam specs also matter.If the cam has a lot of overlap then you need to be a little higher RPM(slightly,not a lot)The accelerator pump on a holley kills mileage.
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Old 04-03-2013, 12:05 AM
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Fill up at a gas station. Record your odometer reading. Drive fifteen or twenty miles in thrid, then turn around and go back and fill up again. Record your gas usage and your mileage. Do the same run again, this time in fourth gear. Fill up again and compare the difference....this way you'll know for sure.
IMO it's better for the engine to be running on cam at 2000 than be labouring at 1200 for any length of time.
If you go through this exercise , please post the result, I'm curious too.....



Duke
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Old 04-03-2013, 04:48 AM
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Also a four bbl carb has a smaller primary so if you don't pull in the secondary's you will get better mileage out of a four bbl.
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Old 04-03-2013, 06:50 AM
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Quote:
Originally Posted by xzero117 View Post
on a car equipped with a double pumper carb settup

is it better to drive around at say 2000rpm in third gear at 30mph with the gas pedal pressed down 25% of the way

or to drive around at 1200 rpm in 4th gear at 30 mph with the gas pedal pressed down 50% of the way ?

in which scenario would I achieve the best mpg's

it's always recommended to stay in as high a gear as possible for fuel economy, but does that still apply if you're dogging it ?
i may be looking at it wrong?? but i don't see how u can have your peddle depressed more at a lower RPM. if u swap the throttle position in your statement i'd agree..
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Old 04-03-2013, 09:24 AM
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Quote:
Originally Posted by xzero117 View Post
on a car equipped with a double pumper carb settup

is it better to drive around at say 2000rpm in third gear at 30mph with the gas pedal pressed down 25% of the way

or to drive around at 1200 rpm in 4th gear at 30 mph with the gas pedal pressed down 50% of the way ?

in which scenario would I achieve the best mpg's

it's always recommended to stay in as high a gear as possible for fuel economy, but does that still apply if you're dogging it ?
More RPM on less throttle in this case. It does two things, it keeps the air velocity up in the primaries which meters better; it keeps the manifod vacuum up preventing the power valve from coming on.

Bogie
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