List your MPG on your transplant 5.7 or 6.1

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67 Dart, stock 5.7 with TTIs and ModMan intake running Megasquirt 2x injection, 4 speed (non O/D), 8 3/4 rear with 3.55s and I believe ~26" tall tires has got me around 16 mpg. It weighs a little under 3400 pounds as I recall from the last time I drove it across the scales at work. Working on a T56 swap now, so hoping to up that to more like 18-20.
 
I am surprised how low these numbers are...your foot must be planted all the time.

My 2wd '96 RAM king cab with a 318 regularity got mid 30s..this was a work truck so I kept (at that time) track of the amount of gas I burned, millage, and gas millage. I thought one of the reasons going to the 5.7 was for great gas millage...hell, our gas thursty /6 got 17 mph...
 
I think a lot of my issue is lack of overdrive. A lot of the swaps aren't necessarily done for daily driver duty either, so they tend to be a little more hopped up. Mine turns 3200+ rpm on the highway cruising 70. I have my AFR target set for around 14.7-14.9 at cruise. Was getting more like 15-16 before a bit of a retune, may be able to squeak a little more out with some more tuning, but it's been running well and I haven't driven it a whole lot lately, so I haven't bothered. I fiddled with it so much when I first did it I was happy to finally get a nice smooth tune and sort of left it at that.

I agree though, the numbers are a little lower than I expected. Granted, these cars aren't exactly aerodynamic compared to the more modern iron, even the trucks to some degree. I might weigh 750 pounds less than a new Charger/Challenger, but when I'm pushing a brick through the wind with an air dam up front it's just as bad if not worse.
 
i agree not as good of numbers as i would think fro ma modern fuel injected motor,,,my dual quad 862 cfm each,,,super charged barracuda,,,391 gears 4 speed no over drive, 33 inch tall tires 2450 rpm if i remember correctly at 60 mph,,,got 10.1 on the high way,,,and after installing E3 spark plugs,,,went up to 13.1 mpg,,,,,not to mention the better throttle responce....


 

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Map63Vette said:
I think a lot of my issue is lack of overdrive. A lot of the swaps aren't necessarily done for daily driver duty either, so they tend to be a little more hopped up. Mine turns 3200+ rpm on the highway cruising 70. I have my AFR target set for around 14.7-14.9 at cruise. Was getting more like 15-16 before a bit of a retune, may be able to squeak a little more out with some more tuning, but it's been running well and I haven't driven it a whole lot lately, so I haven't bothered. I fiddled with it so much when I first did it I was happy to finally get a nice smooth tune and sort of left it at that.

I agree though, the numbers are a little lower than I expected. Granted, these cars aren't exactly aerodynamic compared to the more modern iron, even the trucks to some degree. I might weigh 750 pounds less than a new Charger/Challenger, but when I'm pushing a brick through the wind with an air dam up front it's just as bad if not worse.
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You're spot on as far as gearing...thats whats killing both of us.

Remember...a 300c is turning 1900 rpm or something silly at 70 mph in top gear LOL!
 
383 stroke gen III xfi 273, 650 vac sec, 727, 3.23, and 28" rear tires - is 17.6 highway in a 1969 Barracuda. It took lots of playing with jets. I put 24,000 miles on it that way, and it was an obsession counting mileage. Although that's an average, and includes extreme summer heat, and winters cold or North Eastern PA.
 
My stock 2006 300C gets 15mpg in town with my wife driving it and 22 on the hwy its a thirsty pig but I love it
 
The stock low cr 318 in my '73 Dart does 13-14mpg on average.
2bbl 318 / A518 / 3.91:1 / 8-3/4" rear.

The 318 runs on propane. On gasoline it would do prob. 15-16mpg.

If the 5.7Hemi I've planned to swap in the car doesn't get anything way above 20mpg on propane in this lightweight car I'd be kinda miffed to say the least.
On the other hand, the 5.7 would still mean a 200hp increase over the 318, so that would soften the blow a bit if mpg's aren't much higher.
 
I got just shy of 15 mpg on a 200 mile round trip in 100 degree weather with my 451/6spd combo. I always use 91 octane with no ethanol as that can add at least 1 mpg.
 
15mpg with a 6spd (1 overdrive gear?) sounds fairly 'sad' to be honest.
Somewhere in August I made a similar highway roundtrip and managed 20mpg with my propane 318 cruising around 50mph most of the time.

Have you tuned the engine (for economy) properly?
 
I agree with the comments regarding trans gearing and aerodynamics.
Back in the mid to late 1970s there were some tips published to help increase gas mileage. One of the main things about the earlier cars was that they were not aerodynamically efficient. The article cited the NASCAR aero car modifications that were done to overcome the box shape. It was recommended that a front air dam or chin spoiler be installed along with "cleaning up the under carriage" by fabricating a plastic or thin aluminum sheet that would help the air pass under the car more smoothly. The American cars of the time sat higher off the ground than today's cars and that resulted in a lot of turbulence collecting in the engine compartment which caused drag and thus decreased gas mileage. An overdrive transmission was also advised but the cost of doing that was not practical at the time since there weren't a lot of used ones around that would fit.
The article said that an egg shape is the ideal shape for a car to get the best gas mileage and that the compact cars would gradually assume that shape.

My 5.7 Charger has the aerodynamics and the overdrive tranny but it takes the Multidisplacement function to get 25 on the highway and 16 around town.
 
BigBlockMopar said:
15mpg with a 6spd (1 overdrive gear?) sounds fairly 'sad' to be honest.
Somewhere in August I made a similar highway roundtrip and managed 20mpg with my propane 318 cruising around 50mph most of the time.

Have you tuned the engine (for economy) properly?
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451 bb set on kill, and 80 mph on the interstate. I was hoping for better but that engine is long gone. I'll report back when I get new numbers with a new engine.
 
BigBlockMopar said:
The stock low cr 318 in my '73 Dart does 13-14mpg on average.
2bbl 318 / A518 / 3.91:1 / 8-3/4" rear.

The 318 runs on propane. On gasoline it would do prob. 15-16mpg.

If the 5.7Hemi I've planned to swap in the car doesn't get anything way above 20mpg on propane in this lightweight car I'd be kinda miffed to say the least.
On the other hand, the 5.7 would still mean a 200hp increase over the 318, so that would soften the blow a bit if mpg's aren't much higher.
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That was part of it for me. I'm probably getting about the same mileage I got out of the 318 that was in the car when I bought it, but I've near doubled the power without losing any mileage, so all in all I'm pretty happy. Might have to look into some splash shields and stuff to help close up the underside some. I know I don't have any factory shielding at all right now.
 
wow the numbers are not near as good as i thought they would be. the 2006 dodge ram stock with msd 5.7 would get 21 to 22 at 65 miles and hour and 16 to 18 city. and i know the truck wieghs a hole lot more than the a-bodies.
 
Maybe I'm missing something ?
The best the 07 5.7 4x4 Ram ever gets even with foot out of it road trips mostly freeway is about 18.1-18.3
Around town 13-15
I'm not impressed !!!
Well it does pull well !!!
 
garyfish340 said:
Not to be insulting, but a 318 that can only get 14 mpg needs some attention.
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I'm sure I probably could have done better with mine, but I also didn't really highway commute with it at the time, just around town stuff. Mine was also such a weird combination of parts that I really had no idea what was in it. All I know is that it had a factory 4 bbl intake on it, so I'm guessing I had a pretty nasty port mismatch with my heads. Was one of the smoothest running carbs I've ever dealt with though. Could fire it up and pretty much drive it straight away with no issues in the cold once I got the electric choke hooked up.
 
I could be wrong here. But are most people comparing retro-fit 5.7's, and 6.1's to Dodge Rams, and modern mopars in stock configuration ? I know I have a bigger cam than stock, and a bit of head work, I also have a carb to deal with. Than running through a 2.45 first gear. Before this motor I had a 340 w2 motor, .283/.528, and a carter carb, and it got about 13 max. I made similar power but in the high end range. I could get 17.5 mpg with that too, but I'd burn the top of a piston off doing it. I'm pretty please with my Mpg now, and a little jealous of you fuelie guys.
 
garyfish340 said:
Not to be insulting, but a 318 that can only get 14 mpg needs some attention.
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That's very correct.
Last week I pulled the old timingchain set from the 318 and replaced it with a new set.
The old chain had 1" of play on both sides of the gears...!

After replacement I noticed the engine felt 'tighter' and had a little more torque at low rpms, but it wasn't until I reset the timing on the engine that the real power came to life. Well, as much as one can speak of 'real power' from a 318... lol

The car now pulls away a lot snappier than before and I'm pretty sure this should show in the mileage numbers.
Unfortunatly with the colder temps here mileage will drop anyhow but I will be keeping a close eye on it.
 
Wow, so incidentally we were involved in this M.P.G. post, and you decided to look into you 318, or coincidentally ? 4um good...
 
Well, I may get flamed for dragging up a 5 year old thread but I’d like to hear what more of you guys are getting for fuel mileage.
 
Stock 6.1 Hemi, Fuel injected, headers, 3.91 gears, MT, 0.7 overdrive, 235/50-R17, Bridgestone Turanza Serenity Plus, 26.3" dia.
About 26 IMPG (21 USMPG) highway driving.

RPM calculator.jpg
 
'73 Cuda, 3:55 posi, silver sport four speed powered by a new 392. average mpg is 17.3, highway, around town and some high speeds.
 
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