Need recommendation for a Carb for better MPG!

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The FI systems on the new cars are quite efficient and do get good mileage. But, the newer cars are also lighter, more aerodynamic, and the 6 and 8 speed double overdrive automatic transmissions make a huge difference. If my boxy 70 Dart with a 318 2 barrel, 3 speed auto transmission (and no lock up convertor) and a 3.23 rear gear can get 19, and a 65 Dart with a slant 6 and a 2.76 gear can get 25 mpg, who needs a $2000 FI system.
 
toolmanmike said:
The FI systems on the new cars are quite efficient and do get good mileage. But, the newer cars are also lighter, more aerodynamic, and the 6 and 8 speed double overdrive automatic transmissions make a huge difference. If my boxy 70 Dart with a 318 2 barrel, 3 speed auto transmission (and no lock up convertor) and a 3.23 rear gear can get 19, and a 65 Dart with a slant 6 and a 2.76 gear can get 25 mpg, who needs a $2000 FI system.
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Plus a lot of the tech on new cars is more for the insane pollution standards then anything else followed by performance (hp) and mileage.
 
toolmanmike said:
The FI systems on the new cars are quite efficient and do get good mileage. But, the newer cars are also lighter, more aerodynamic, and the 6 and 8 speed double overdrive automatic transmissions make a huge difference. If my boxy 70 Dart with a 318 2 barrel, 3 speed auto transmission (and no lock up convertor) and a 3.23 rear gear can get 19, and a 65 Dart with a slant 6 and a 2.76 gear can get 25 mpg, who needs a $2000 FI system.
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Unless if you are inferring to a "Smart Car", I think most cars are heavier today than the pass. My truck is 6,500 lbs and I believe the Challengers and Chargers are in the 4,500 range, thats about 1,000 lbs. more today for each.
 
Swinger 340 said:
Unless if you are inferring to a "Smart Car", I think most cars are heavier today than the pass. My truck is 6,500 lbs and I believe the Challengers and Chargers are in the 4,500 range, thats about 1,000 lbs. more today for each.
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Those are heavier for sure. There's a lot of thin gauge steel and plastic parts in the new cars. Even so, the heavy ones get decent mileage because of the efficiency and the transmissions. I could put a 8 speed auto in my Swinger and probably get mid to late 20's for mileage. Same with a 6 speed manual in my 66 Dart 273 car. A 833 o/d will get mid 20's. The new cars may weigh a bit more because of all the safety features. They are also well insulated for sound than the old cars were. My 66 weighs right around 3000# where my wife's Buick Envision weighs somewhere over 3500#. I haven
t compared size but both take up roughly the same space in the garage. Just a rough comparison, not like comparing a Suburban and a Honda Civic.
 
About 18 years ago, I see that I took out the 323s and put in 294s. Would it be worth going down to a 276? I guess I would have a 294 and 323 to trade/sell. In the meantime, I'm going to work on getting the 340 tuned. You guys are wonderful!
 
toolmanmike said:
Along those same lines, The 340 never came in a 2 barrel version.
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Very similar to engines like the 403 Olds, 425 Olds and 430 Buick. All of each of those three engines only came one way. In high performance tune with a four barrel. Even the 403s that made it into station wagons. They were the exact same engine as was in the Trans Ams for those years. They would flat out get it.
 
Valveguy said:
About 18 years ago, I see that I took out the 323s and put in 294s. Would it be worth going down to a 276? I guess I would have a 294 and 323 to trade/sell. In the meantime, I'm going to work on getting the 340 tuned. You guys are wonderful!
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Did you notice much of a mpg difference between the 3.23 vs 2.94 swap ?
The 2.76 is a even smaller ratio drop.
 
Valveguy said:
About 18 years ago, I see that I took out the 323s and put in 294s. Would it be worth going down to a 276? I guess I would have a 294 and 323 to trade/sell. In the meantime, I'm going to work on getting the 340 tuned. You guys are wonderful!
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Nope. Not at all.
 
RustyRatRod said:
Nope. Not at all.
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I would hold onto the 3.23. That's a great gear. Look at it this way. IF you find something that picks your mileage up pretty good, the 3.23 might be something to think about swapping back in.
 
if your looking for a carb to build for this project try a 6210 holley you can find on fb for 100 and take the 4brl rod off and run the primaries cause this carb you can get any jet any pump cam any power valve ect. ect. more tunable than the tq for what you want there are more variables
 
cwkerr007 said:
if your looking for a carb to build for this project try a 6210 holley you can find on fb for 100 and take the 4brl rod off and run the primaries cause this carb you can get any jet any pump cam any power valve ect. ect. more tunable than the tq for what you want there are more variables
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I don't get it, why have a 340 and detune it to become a sled? I would want my 340 to get 8 MPG and become a "Fire Breathing Animal".
 
Swinger 340 said:
I don't get it, why have a 340 and detune it to become a sled? I would want my 340 to get 8 MPG and become a "Fire Breathing Animal".
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Because in reality you can actually have both, if you know what you're doing. The OP's 5-speed overdrive trans is a huge factor in being able to do that.

Optimize WOT mixture for max power, tune cruise mixture to be at least stoich or slightly leaner, run vacuum advance and initial timing + advance curve that gives ample advance at lower RPMs, good ratio spread in transmission for decent leverage on take-off and low-RPM cruising at speed, cam specs that give decent cylinder filling and low reversion at the expected cruise RPMs... and there you go. Several posts in this thread from guys who have actually done it.

@Valveguy just focus for now on getting your tune optimized and go from there. Earlier you said you didn't notice much difference in performance between your current 340 and your old 318 2-bbl from when you were in high school, that indicates your 340 is not running the way it should. 318 is a putt-putt "get mom to the grocery store and back" engine in stock form.
 
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MopaR&D said:
Because in reality you can actually have both, if you know what you're doing. The OP's 5-speed overdrive trans is a huge factor in being able to do that.

Optimize WOT mixture for max power, tune cruise mixture to be at least stoich or slightly leaner, run vacuum advance and initial timing + advance curve that gives ample advance at lower RPMs, good ratio spread in transmission for decent leverage on take-off and low-RPM cruising at speed, cam specs that give decent cylinder filling and low reversion at the expected cruise RPMs... and there you go. Several posts in this thread from guys who have actually done it.

@Valveguy just focus for now on getting your tune optimized and go from there. Earlier you said you didn't notice much difference in performance between your current 340 and your old 318 2-bbl from when you were in high school, that indicates your 340 is not running the way it should. 318 is a putt-putt "get mom to the grocery store and back" engine in stock form.
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This is ALL very helpful, Thank You!!
 
I appreciate what you are saying but I'm not that guy. Everyone is different. I'm mostly in love with the body style and I would have bought the Demon if it had a slant six. Yes, the extra power is absolutely fun from time to time but it's not a got-to-have for me. I have a 2010 hemi Challenger, and I average 26 mpg, for real on my commute. I just like staying away from the gas stations as long as I can. It can be done. Everyone here has been fantastic, and I love the variety of comments!
Swinger 340 said:
I don't get it, why have a 340 and detune it to become a sled? I would want my 340 to get 8 MPG and become a "Fire Breathing Animal".
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.
 
I forgot you had a 5 speed ya I definitely wouldn't go any higher with rear gear, I'd be going deeper 3.23/3.55 but that's me :)

Lowest rpm don't necessarily mean most efficient rpm. It takes X amount of hp to power your car down the highway no matter what rpm your turn your engine is only making the needed hp or otherwise you'd be accelerating or decelerating not cruising at speed. Say it takes 40 hp @ 75 mph it takes a certain amount of fuel with in a narrow range to make that hp question is what are the right circumstances that it will be most efficient rpm, timing etc..
 
MopaR&D said:
Because in reality you can actually have both, if you know what you're doing. The OP's 5-speed overdrive trans is a huge factor in being able to do that.

Optimize WOT mixture for max power, tune cruise mixture to be at least stoich or slightly leaner, run vacuum advance and initial timing + advance curve that gives ample advance at lower RPMs, good ratio spread in transmission for decent leverage on take-off and low-RPM cruising at speed, cam specs that give decent cylinder filling and low reversion at the expected cruise RPMs... and there you go. Several posts in this thread from guys who have actually done it.

@Valveguy just focus for now on getting your tune optimized and go from there. Earlier you said you didn't notice much difference in performance between your current 340 and your old 318 2-bbl from when you were in high school, that indicates your 340 is not running the way it should. 318 is a putt-putt "get mom to the grocery store and back" engine in stock form.
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You read my post wrong. What I said was, I did not notice much of a difference between the 318 and 340 until I added the headers and 2.5" exhaust. I had 318 exhaust manifolds on it at the time. Night and day once I installed the proper exhaust. The 318 gave me 14 MPG while the 340 was 10 MPG, but a lot more fun.
 
Way back in the late '70's, I put a 318 cam in my 340 with 10:1 compression, an SP2P manifold and the original 4425S Carter AVS. with 2.94 gears and 27" tall tires, I got 22-24 MPG. The car is as shown, a '68 Barracuda FB FS. I did convert to a desert cooler radiator and a 14" Flex-a-lite electric fan to eliminate that power draw. Never overheated in 117°F heat on a drive to Tuscon from Orange County. Once drove it from South SF to Irvine on one tank of gas. On fumes when I got there, but made it. About 380 miles on 16 gal. I wish i never changed from that configuration.
 
RLF Cuda said:
Way back in the late '70's, I put a 318 cam in my 340 with 10:1 compression, an SP2P manifold and the original 4425S Carter AVS. with 2.94 gears and 27" tall tires, I got 22-24 MPG. The car is as shown, a '68 Barracuda FB FS. I did convert to a desert cooler radiator and a 14" Flex-a-lite electric fan to eliminate that power draw. Never overheated in 117°F heat on a drive to Tuscon from Orange County. Once drove it from South SF to Irvine on one tank of gas. On fumes when I got there, but made it. About 380 miles on 16 gal. I wish i never changed from that configuration.
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I love this! I too put 27" tires on the back. I just might consider trying try this after I do the tune up depending upon how things go. Not sure how to get a 318 cam yet. THANK YOU! 380 miles on a tank would be awesome!
 
OK, it's going to take me some time but I'm going to follow what I see as being the consensus here and do a tune up. One thing at a time, I don't have a vacuum gage. Any recommendations? Thanks!!
 
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