mpg on my 340

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68cudaauto

original mopar man
Joined
Jan 5, 2015
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Location
addis,la.
Very satisfied with my mpg for hwy driving, was worried because of the poor 10 mpg I was getting in town driving. I have a 68 cuda with a 340 and 750 quick fuel carb, jetting at 66 with a power valve on the primary, 72 jetting in the rear. Idle circuit adjusted to 3/4 turn out on both. Made a test run this week and took off down a river road with no red lights, I got 16 mpg, would like to hear a few similar mpg avgs for similar set ups.3.23 gears and 904 3 speed automatic, headers and dual exhaust.
 
17 mpg in a '70 dodge truck. 340, TQ, auto, MP cam (.474/280), headers, 2.76 gears going from Illinois to Colorado. I also leaned the metering rods before leaving
 
I swear this is true. Just before the "double nickel" speed limit was introduced, I decided to make the RR into a "driver" and build a fun/ street/ drag car. I also had a 64 Dodge at the time. This was about 72--early 73. I bought a low miles 340 out of a Duster and installed it into the what had been a V code 70 RR so, 18 spline 4 speed, 3.54 Dana, lots of tools in the trunk, and "add on" A/C. That thing even with my not so careful driving, on a highway trip would get 17.5. the best the 440 ever got with an 800 DP Holley, and headers, was 13.8. This was NOT a lightweight car. I weighed it once I think it was 3860 lbs with the 440, headers, and 4bbl Ed intake.

With gearing and rear tires, it ran right at 3K RPM at 70 MPH.

This was when we were beginning to have "gas shortages" or at least fuel was "going up." In the winter of 73 I got stuck on Navy Shore Patrol in downtown San Diego. Damned station operators would leave the signs lit up and powered, you'd be driving down in the freeway cut and go "up" the ramp for some fuel and the station would be locked up!!!

The 340 RIGHT after install. I was BROKE!!! Ran it for awhile with 318 manifolds and single exhaust. In this photo the A/C has not been re-installed. Can't afford valve covers at this point, LMAO

_mg_6209cs-jpg.1714606233


This was taken in either 73 or 74, and it had the 340 and headers by that time. I had driven from San Diego (Miramar) to N Idaho, this is my folk's back yard.

81sruds.jpg
 
I swear this is true. Just before the "double nickel" speed limit was introduced, I decided to make the RR into a "driver" and build a fun/ street/ drag car. I also had a 64 Dodge at the time. This was about 72--early 73. I bought a low miles 340 out of a Duster and installed it into the what had been a V code 70 RR so, 18 spline 4 speed, 3.54 Dana, lots of tools in the trunk, and "add on" A/C. That thing even with my not so careful driving, on a highway trip would get 17.5. the best the 440 ever got with an 800 DP Holley, and headers, was 13.8. This was NOT a lightweight car. I weighed it once I think it was 3860 lbs with the 440, headers, and 4bbl Ed intake.

With gearing and rear tires, it ran right at 3K RPM at 70 MPH.

This was when we were beginning to have "gas shortages" or at least fuel was "going up." In the winter of 73 I got stuck on Navy Shore Patrol in downtown San Diego. Damned station operators would leave the signs lit up and powered, you'd be driving down in the freeway cut and go "up" the ramp for some fuel and the station would be locked up!!!

The 340 RIGHT after install. I was BROKE!!! Ran it for awhile with 318 manifolds and single exhaust. In this photo the A/C has not been re-installed. Can't afford valve covers at this point, LMAO

_mg_6209cs-jpg.1714606233


This was taken in either 73 or 74, and it had the 340 and headers by that time. I had driven from San Diego (Miramar) to N Idaho, this is my folk's back yard.

81sruds.jpg
 
image.jpeg
About a month ago, I had a 340 TA 6 pack motor put in my 68 Dodge Dart GT convertible. So far, I am getting 11 to just over 13 mpg depending how much I am stomping the gas pedal.
I am hoping to get 15 mpg on the highway. I'll repost after I go for a long trip.
 
60,000 original mile 318 1973 Satellite 904, 2.76, 3700#

2 bbl, 2.25 duals, manifolds, 225/70/15 rear tires.

14.5 in mixed driving.

I think it can do better.
 
I got 26 mpg out of my 340 challenger 727 3:23 at 55mph between Lawton and Norman OK. Granted the wind was perfectly behind me. My buddy's 454 4spd 4.11 chevelle only did 12. He was pissed.
 
My 360 averages 11-12 MPG. Best is 15.5 cruising at 3000 RPM on the freeway.

Stock low compression 360 with MP 268/272-450/455 cam, 904 trans, 3.23 gears, 600 carb, headers
 
I dont know what the conversion to mpg is but my Duster gets around 150km from 40ltrs

360, 4 speed ,3.73 gearing
 
With a mild cammed 318 and 3.23 gears behind a 904 auto, I get 11 mpg around town and 13 on the highway. But I'm sure my carb is way out of whack and I could do better.
 
THANKS FOR THE REPLIES, 67 DART, MY FIRST CAR WAS A LEMON TWIST 1970 ROADRUNNER, 4SP, 383, NO A/C, KEPT IT FOR 5 YEARS AND SOLD IT FOR $1500, I LOVED THAT CAR, GOT ABOUT 14MPG WITH THE BEAST.
 
I got 26 mpg out of my 340 challenger 727 3:23 at 55mph between Lawton and Norman OK. Granted the wind was perfectly behind me. My buddy's 454 4spd 4.11 chevelle only did 12. He was pissed.
IMPRESSIVE, I WOULD TAKE THAT IN A HEARTBEAT
 
I got 26 mpg out of my 340 challenger 727 3:23 at 55mph between Lawton and Norman OK. Granted the wind was perfectly behind me. My buddy's 454 4spd 4.11 chevelle only did 12. He was pissed.
Me thinks, you '' BEEN DRINKIN !"--------LOL
 
71 dart, bench seat a/c car, 96 5.2 magnum stone stock other than a dual plane m1 and a 72 340 thermoquad, headers, dual exhaust 904/ and a 3:23 8 3/4, easy 21 MPG highway
 
Best ever with my 71 Dart Swinger with the 318 or 340 was 20 mpg, but that was pretending I had an egg between my foot and the gas, keeping it at 55, no stopping or starting, AC off.
Normal was about 14-15.
3.23, pretty darn factory stock in every way.
36psi in tires.
 
71 dart, bench seat a/c car, 96 5.2 magnum stone stock other than a dual plane m1 and a 72 340 thermoquad, headers, dual exhaust 904/ and a 3:23 8 3/4, easy 21 MPG highway

What's your average/mixed with that setup?
 
Quite a few years ago my 71 Duster 340 was running high 12's with a LD intake and a big Hyd cam. I swapped out the 4.56 chunk for a 3.23 and hit the highway for NY from FLA. I got 18 mpg. 4 speed car. My truck with EFI and overdrive wont even get that.
 
Very satisfied with my mpg for hwy driving, was worried because of the poor 10 mpg I was getting in town driving. I have a 68 cuda with a 340 and 750 quick fuel carb, jetting at 66 with a power valve on the primary, 72 jetting in the rear. Idle circuit adjusted to 3/4 turn out on both. Made a test run this week and took off down a river road with no red lights, I got 16 mpg, would like to hear a few similar mpg avgs for similar set ups.3.23 gears and 904 3 speed automatic, headers and dual exhaust.
66/72 sounds kindof lean, I can barely hit 60mph with 66's, and there's nothing left over for PT acceleration.But if you can make it work, hey, MorePowerToYa. 10/16 is pretty good spread.
Our A's only take between 40 and 50 hp to maintain 60 mph, so if I estimate 45hp, that would be 3.75 gallonsUS per hour. Of course 60 mpg is a mile a minute, so those 3.75 gallons will move you 60 miles. That then looks like 60 miles per 3.75 gallons which reduces to 16mpgUs. So you are right on target.
Mind you this is for an A/F more suited to WOT,So I would expect this to be a minimum mpg.


60,000 original mile 318 1973 Satellite 904, 2.76, 3700#
2 bbl, 2.25 duals, manifolds, 225/70/15 rear tires.14.5 in mixed driving.
I think it can do better.
I bet you can. 16 should not be hard, at steady-state cruise

I dont know what the conversion to mpg is but my Duster gets around 150km from 40ltrs, 360, 4 speed ,3.73 gearing
150/40=3.75 km/liter.Times that by 4.55 to convert from liters to Canadian gallons, and times .62 to convert to miles is 10.58 mpgImp. To convert that to Usg, times it by .8, equals 8.46 mpgUS, as already said. I just love the math exercise

With a mild cammed 318 and 3.23 gears behind a 904 auto, I get 11 mpg around town and 13 on the highway. But I'm sure my carb is way out of whack and I could do better.
Yeah you are probly a little off-tune too.

I got 26 mpg out of my 340 challenger 727 3:23 at 55mph between Lawton and Norman OK. Granted the wind was perfectly behind me. My buddy's 454 4spd 4.11 chevelle only did 12. He was pissed.
I believe that could be possible




Here's my recipe;
So, take one 10.9 aluminum headed 360 with a 223* cam, headers and AirGap. Install a 600Vac Secondary.Get the timing right, and leannnnnnnnnnnn out the low speed circuit. Then put a teensy bit back in for safety sake. With a stick and wicked highway gears, expect into the 30s mpgUS@80mph. Easy recipe.Just leannnnnnnnn her out.
And a wagon load of timing.Just pour it in, and pour it in. I gave her 50 then 55 then 57,60,&62, then I ran out. She still was taking it.( For those that are curious; I have a dash-mounted, Dial-Back Timing Gizmo. Best tool I ever bought.The range is 15 degrees) .
How is that possible you ask? Ok,Ok, I'll tell you.
I was using the GV .78overdrive behind an A833-O/D and 3.55s, so my final drive ratio, in double O/D, was 1.97, and 80mph was 1999 rpm calculated.And I had modded the carb to accept wire restrictors in the idle wells. And I had several wire-sets with various cross-sections. I was not yet running on the edge.

Fast forward a few years.
Gone are; the 223*, the double O/D, and the 600.
Swapped in are ; a 230*, .78 O/D, and a 750DP.
I get about 10 USg combined; no more long trips........



 
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I wish I had bought THREE of those dash mount Carter anti-knock spark retarders back in 1979, where you have a knob to set the spark to retard when the sensor hears pre-ignition.
 
so when I am reading all those numbers.... why do I have such a bad milage ? 340.. 727 and 3.23... TQ carb..
What is the secret ??

Greetings Juergen

And no...I don´t jump in the gaspedal hard !! the 11 mpg
is with 55 -60 mph on the autobahn....
 
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