thinking about going 2 barrel
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Thanks hoxiii for a very coherent response.
I have been considering going to fuel injection and your arguments I think have convinced me to go sooner rather than later. It will allow me to turn across the entire driving range.
I have to agree that some of these guys claiming 15 must have speedometers that are off. When I went digital with my speedo my mileage suddenly dropped.
Peter
I have been considering going to fuel injection and your arguments I think have convinced me to go sooner rather than later. It will allow me to turn across the entire driving range.
I have to agree that some of these guys claiming 15 must have speedometers that are off. When I went digital with my speedo my mileage suddenly dropped.
Peter
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Originally Posted by hoxiii
This is where you run into efficiency limits. A mildly built motor with a properly jetted carburetor will almost always get better mileage than a stock motor of the same design. The built motor will tend to have a higher compression ratio and such, which in turn increases the thermal efficiency of the motor. Alot of times the motor will use the same amount of fuel to return more power, less fuel for the same power, or slightly less fuel for slightly more power.
It isn't uncommon for properly tuned (jetted, recurved, dyno tuned, whole nine yards) medium displacement motors (300-400 cubes) to return 20 mpg while their stock counterparts barely eeked out 10. Now mind you, having an engine properly dyno tuned is by no means cheap but it is about the only way to actually get mileage out of one of these motors.
And as for the question about the Edelbrock being of a q-jet design, the answer is no. The Edelbrock Performer series uses metering rods like a quadrajet but is a squarebore design (according to the company itself). UNLESS you buy an Edelbrock q-jet (they bought the rights to the design from Rochester). Then you have a q-jet with Edelbrock stamped on it, but they're $$$$. However, i don't even know if they still make those. For what they cost, most people were turned off.
Justin
It isn't uncommon for properly tuned (jetted, recurved, dyno tuned, whole nine yards) medium displacement motors (300-400 cubes) to return 20 mpg while their stock counterparts barely eeked out 10. Now mind you, having an engine properly dyno tuned is by no means cheap but it is about the only way to actually get mileage out of one of these motors.
And as for the question about the Edelbrock being of a q-jet design, the answer is no. The Edelbrock Performer series uses metering rods like a quadrajet but is a squarebore design (according to the company itself). UNLESS you buy an Edelbrock q-jet (they bought the rights to the design from Rochester). Then you have a q-jet with Edelbrock stamped on it, but they're $$$$. However, i don't even know if they still make those. For what they cost, most people were turned off.
Justin
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From: Pittsburgh
Then it isn't a quadrajet. The big deal about the Q-jet is the fact that it is a spreadbore carburetor. That's where it gets it's inherent efficiency from.
The small primaries keep the air velocity up which improves throttle response and part throttle fuel economy through better fuel atomization. Get rid of the small primaries and you lose part of the air velocity and atomization, to the detriment of economy and part throttle driveability.
On a 4bbl carb, the design and setup of the primaries is where mileage and most of your useable power is because that's where you spend most of your time. You could wire the secondaries shut on a 4bbl and you wouldn't notice the difference 90% of the time (unless you always have your foot in it and use every gear for all it's worth, if you do nothing will help your mileage).
Simply, as has been stated, your best carbureted mileage will be from a properly jetted vacuum secondary spreadbore 4 bbl carburetor. The most common of which just happens to be the Rochester Quadrajet.
Justin
The small primaries keep the air velocity up which improves throttle response and part throttle fuel economy through better fuel atomization. Get rid of the small primaries and you lose part of the air velocity and atomization, to the detriment of economy and part throttle driveability.
On a 4bbl carb, the design and setup of the primaries is where mileage and most of your useable power is because that's where you spend most of your time. You could wire the secondaries shut on a 4bbl and you wouldn't notice the difference 90% of the time (unless you always have your foot in it and use every gear for all it's worth, if you do nothing will help your mileage).
Simply, as has been stated, your best carbureted mileage will be from a properly jetted vacuum secondary spreadbore 4 bbl carburetor. The most common of which just happens to be the Rochester Quadrajet.
Justin
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From: south louisiana
Originally Posted by workingdog
I've got a midly built 390 with an Edelbrock 1406 4 barrel carb. I'm getting about 8 to 9 mpg. I've taken a look at adjusting the Edelbrock and have pretty much come to the conclusion that it's running about as lean as it can.
What are suggestions for a good 2 barrel that I might be able to find on ePay. I have an Edelbrock Performer RPM intake.
Peter
What are suggestions for a good 2 barrel that I might be able to find on ePay. I have an Edelbrock Performer RPM intake.
Peter
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Originally Posted by Bear 45/70
Alot of these higher mpgs come from higher rear axle ratios (3.50 and up), so the motor doesn't run as many rpm. Also, even though a lot of them won't admit it, their odometers are off and their mileage numbers reflect that error.
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Properly set up and dialed in, a vacuum secondary carb gives the engine the 'correct' amount of fuel and air based on actual engine demand, and not the arbitrary demand of yr heavy right foot. 
With a mechnical secondary carb, you can and do often provide more throttle opening than the engine can make use of.
Mech secondary carbs often do provide much more of a 'kick in the pants' feel when you mash the skinny pedal, but that is largely due to the fact that they have secondary accel pump/squirters that just dumped a load of raw fuel in with all that excess air you just made available a the same time.
With a mechnical secondary carb, you can and do often provide more throttle opening than the engine can make use of.Mech secondary carbs often do provide much more of a 'kick in the pants' feel when you mash the skinny pedal, but that is largely due to the fact that they have secondary accel pump/squirters that just dumped a load of raw fuel in with all that excess air you just made available a the same time.
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Post Fiend
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From: Union, Washington
Originally Posted by bmc69
FWIW..I picked up 2 mpg (highway) on my '73 F-250 CS w/ 360 when I took off the 2V and stuck on a factory junkyarded cast-iron 4V intake and a Holley 600 vac secondary carb (good ole cheap List-1850 model). It went from 10 to 12 mpg..keeping my foot out of it of course.
Logistics Pro
Joined: Apr 2005
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The best I got got out of my 360 with the 2bbl Motorcraft was 8.
I swaped it for a 390, put in a 4bbl manifold with a 600CFM H*lley and I still get 8. Got a little over 8.5 once. Swapped my 4:10s for 3:73s, didn't help any. I guess some trucks are just thirsty.
I swaped it for a 390, put in a 4bbl manifold with a 600CFM H*lley and I still get 8. Got a little over 8.5 once. Swapped my 4:10s for 3:73s, didn't help any. I guess some trucks are just thirsty.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Originally Posted by workingdog
customcab66,
What gears and tranny are you running? There's not way you're pushing that giant brick of a truck through the air at 65 mph and getting 20 mpg.
Peter
What gears and tranny are you running? There's not way you're pushing that giant brick of a truck through the air at 65 mph and getting 20 mpg.
Peter
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Originally Posted by Bear 45/70
I agree, just not possible with the science of physics we have to live by.
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Originally Posted by hoxiii
Then it isn't a quadrajet. The big deal about the Q-jet is the fact that it is a spreadbore carburetor. That's where it gets it's inherent efficiency from.
The small primaries keep the air velocity up which improves throttle response and part throttle fuel economy through better fuel atomization. Get rid of the small primaries and you lose part of the air velocity and atomization, to the detriment of economy and part throttle driveability.
On a 4bbl carb, the design and setup of the primaries is where mileage and most of your useable power is because that's where you spend most of your time. You could wire the secondaries shut on a 4bbl and you wouldn't notice the difference 90% of the time (unless you always have your foot in it and use every gear for all it's worth, if you do nothing will help your mileage).
Simply, as has been stated, your best carbureted mileage will be from a properly jetted vacuum secondary spreadbore 4 bbl carburetor. The most common of which just happens to be the Rochester Quadrajet.
Justin
The small primaries keep the air velocity up which improves throttle response and part throttle fuel economy through better fuel atomization. Get rid of the small primaries and you lose part of the air velocity and atomization, to the detriment of economy and part throttle driveability.
On a 4bbl carb, the design and setup of the primaries is where mileage and most of your useable power is because that's where you spend most of your time. You could wire the secondaries shut on a 4bbl and you wouldn't notice the difference 90% of the time (unless you always have your foot in it and use every gear for all it's worth, if you do nothing will help your mileage).
Simply, as has been stated, your best carbureted mileage will be from a properly jetted vacuum secondary spreadbore 4 bbl carburetor. The most common of which just happens to be the Rochester Quadrajet.
Justin
If the design of the base plate determined the style of carb...how do you explain the fact that there are square-bore and spread-bore Holleys??
The design of the carb and the style of the base plate are two very different things!!
If the baseplate determined the style.. then they would be called spreadbores and not Q-jets!
Not all Q-jets are spreadbores and not all spreadbores are Q-jets!
Last edited by fomocofan; Aug 20, 2006 at 05:00 PM.