What MPG are you 340 guys getting?

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I don't have a 340 but shouldn't be too different, here goes:

I drove to Louisville, CO and back a few weeks ago from Ogden UT. area. About 500 miles one way. I do this almost every year.
I'm keepin' it around 70 mph so I try to stay around 3000 RPM.
I have a 360 with 10.2 compression, Lunati Voodoo Roller cam, alum. heads and an Edel airgap intake. Topped with a 750 CFM Street Demon.
A999 Transmission and 3.21 rear diff gears (8 1/4 rear).
The tires are 25.7 in. diameter

I got between 11.5 and 14.5 mpg this time due to going in to 40 to 55+mph winds and as well as crosswinds.
Last year I got a best of almost 17.5 mpg with a favorable 40mph tailwind.
On calmer days I get between 15-16 mpg.

Few takeaways. I love that Street Demon carb, it's simple, and has some Thermoquad elements to it.
An OD transmission is definitely in the near future as I'm going to install an 8 3/4 rear with 3.55 gears soon.
I got an A500 (42RH) in my garage from a 1992 Dakota 2wd that I'm going to rebuild.
And yeah, I need to finish my aftermarket A/C install.
 
I got around 14mpg in my '70 Duster driving from Charlotte, NC to Augusta, GA cruising at 75-80mph. Stock 5.9L Magnum short block, 9:1 compression, 222° @ .050" hyd roller cam, heavily ported Edelbrock heads, shorty headers, 750cfm Street Demon carb. Around 450 HP based on 1/4-mile trap speeds. I think the biggest draw is the cheap loose 2600-rpm stall converter in front of the 904 trans that seems to slip quite a bit as the car currently has 2.94 gears and 27" rear tires. With an overdrive manual trans that could keep it spinning in the lower-2000s RPM range and no slippage from a torque converter I think it would break into the low 20s for mpg.
 
MopaR&D said:
I got around 14mpg in my '70 Duster driving from Charlotte, NC to Augusta, GA cruising at 75-80mph. Stock 5.9L Magnum short block, 9:1 compression, 222° @ .050" hyd roller cam, heavily ported Edelbrock heads, shorty headers, 750cfm Street Demon carb. Around 450 HP based on 1/4-mile trap speeds. I think the biggest draw is the cheap loose 2600-rpm stall converter in front of the 904 trans that seems to slip quite a bit as the car currently has 2.94 gears and 27" rear tires. With an overdrive manual trans that could keep it spinning in the lower-2000s RPM range and no slippage from a torque converter I think it would break into the low 20s for mpg.
Click to expand...
Hmm... Interesting, my cam duration at .050 is 219/227. I honestly could've gone one step up (231/239 at .050).
- But this one has been pretty good to me, especially on the street, great midrange power.
But it does run out of steam on the high end.
 
Cuprum-74 said:
Hmm... Interesting, my cam duration at .050 is 219/227. I honestly could've gone one step up (231/239 at .050).
- But this one has been pretty good to me, especially on the street, great midrange power.
But it does run out of steam on the high end.
Click to expand...

My cam is a custom grind roller with fast ramps, 272 adv duration and hair under .550" lift so it's a bit bigger than the .050" numbers might indicate esp compared to flat tappet. The ported heads help with the top end too, makes power up to about 6k with somewhat restrictive exhaust. I think it'll pick up a lot with the Doug's headers I have yet to install and 3" pipes to the 2.5" mufflers instead of 2.25" head pipes with some tight bends going into 2.5" in it currently.
 
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