mpg on my 340

68cudaauto said
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.

YY1 said
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

ktm071983 said
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

autopar3000 said
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........