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| Finally have a MPG figure for my dart - a little disapointed https://slantsix.org/forum/viewtopic.php?t=13487 |
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| Author: | MileHighDart [ Mon Jun 27, 2005 9:34 am ] |
| Post subject: | Finally have a MPG figure for my dart - a little disapointed |
Well, finally have my speedometer fixed in the dart so now I can finally figure out what kind of gas milage I'm getting. Filled up last sunday, drove to work all week and filled up again saturday morning. Did the math and i'm getting 18.9 mpg. I was hoping for a little better, maybe something like 23 or 24 since 95% of my driving is highway miles, 55-65 mph. My setup is currently, 68Dart, 225slant, supersix with freshly rebuilt carb, still have 1-7/8" pipe coming off the exhaust manifold, then it steps up to 2" pipe with a turbo muffler, a complete new 2.25inch exhaust system is coming soon, 904-auto, 7-1/4" rear with 2:76 gears. Ign timing is set at 8 degrees advancedbut could probably advance a little more. Also i'm at 5500 feet elevation so I probably need to jet the carb down a little bit for this altitude. Any other ideas on how I could improve the milage a little bit ? Or is 19mpg average for a slant powered dart ? |
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| Author: | SlantSixDan [ Mon Jun 27, 2005 9:52 am ] |
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19mpg is very normal for your setup. The new exhaust will probably help a little, as will a good distributor recurve, choke adjustment and carb rejet to better match your high-altitude conditions (I drove \6 cars at 5500 feet myself for over a decade...). You can squeeze a little more mileage with NGK ZFR5N spark plugs gapped to 0.040" (did you say electronic ignition?), 35 lbs of air in the tires, a careful alignment... |
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| Author: | MileHighDart [ Mon Jun 27, 2005 10:01 am ] |
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Yes, I forgot to mention. It does have the mopar electronic ignition with orange box. I have a freshly rebuilt front end and a good alignment. I'm running about 30lbs air in my tires, but they are a little bigger than stock 225/60/15's I'll have to read up on the distributor recurve thing, cause I dont know much about it. I'll definately pick up a set of those NGK plugs and give them a try, and maybe I can get the exhaust done soon. Then i'll start messing with the carb and dist. recurve. I want to try and get my milage up as much as possible since I use the dart for commuting to work, its about 60mile round trip. |
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| Author: | SlantSixDan [ Mon Jun 27, 2005 10:11 am ] |
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Quote: Yes, I forgot to mention. It does have the mopar electronic ignition with orange box.
That's an important detail. Did you do any work at all on the centrifugal advance? That distributor ships with one (and only one) super-lightweight mechanical advance spring. This dumps in all the mech advance all at once right off idle, which creates a lot of pinging unless you retard the base timing and restrict the vacuum advance well back from where they could otherwise be. The effect on mileage is large and negative. If the two choices are "MP single-light-spring and restricted vacuum curve" or "Factory-type mechanical and vacuum curves", then factory is the way to go. Of course, custom curving is better than either. Take a look at Gearhead's recent comments.
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| Author: | vynn3 [ Mon Jun 27, 2005 12:06 pm ] |
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Assuming you have steel 15" wheels, I would think that plus the bigger tires will make a difference, too. It's all unsprung weight, after all, and the added resistance of the tire width doesn't help. VM |
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| Author: | Dart270 [ Mon Jun 27, 2005 12:37 pm ] |
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Timing curve and carb jetting are the biggest parts, assuming ignition is strong and everything else is OK (good comp on all cyls, etc...). Wheels/tires do not make a big difference, esp in hwy driving. I have gotten up to 26-27 mpg in my 64 Dart with 16x8 wheels... You might see a 1-2 mpg difference around town, but even that is unlikely. I would suggest mapping your timing curve using a good advance timing light (Sears or similar), and get an O2 sensor installed in your new 2.25" exhaust and get an AF ratio gauge so you can tune your carb for best (lean) cruise mixture. Lou |
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| Author: | Dartvader [ Thu Jun 30, 2005 7:07 pm ] |
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I know I sound like a broken record with this, but check the voltage at your alternator, and then again at the high side of your ballast resistor. If there is more than .5 volts drop, then the wiring connectors are robbing you of vital energy needed to run your ignition efficiently. Most of the old Mopars I have checked have 1.5 volts or more lost there. That will definately rob you of fuel efficiency. The alternator voltage should be 13.5 to 14.1 at idle. Get back to us and let us know what your alternator is putting out at idle. It could be the entire charging system is below par. These Mopar electronic ignition systems loose alot when the voltage drops. |
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