Gas Mileage???

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y2swinger69

y2swinger69

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I just attended the 16 chryslers at carlisle and finally after 8k miles after beING restored I calculated mileage! First off I have a 69 dart with the numbers driveline. 340 stock 727 and 3.23 suregrip. I'm running a 255/60/15. I'm only averaging 10mpg running at 60mph. I feel that's poor mileage and was wondering what yall are getting. The car runs great but is there something going on with me achieving these numbers. I'm running 93 octane also. Thanks in advance
 
y2swinger69 said:
I just attended the 16 chryslers at carlisle and finally after 8k miles after beING restored I calculated mileage! First off I have a 69 dart with the numbers driveline. 340 stock 727 and 3.23 suregrip. I'm running a 255/60/15. I'm only averaging 10mpg running at 60mph. I feel that's poor mileage and was wondering what yall are getting. The car runs great but is there something going on with me achieving these numbers. I'm running 93 octane also. Thanks in advance
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How big of a carb ? 10 mpg does seem low
 
I also drove to Carlisle in my 67 Dart GT "decoy" with 30 over 318 with Comp 268 cam 600 holley. I averaged 13 to 16 over the 2100 miles. Lots of site seeing and going thru towns and running 70-75 on interstate.
 
My stock 318 gets 20+ but that doesn't count against your 340 that is a hot rod by comparison.
 
factory 340 super big valve heads, suck and flow well for power, with the really high compression, the smaller port heads are more for torque and velocity, that will give you mileage. and factory 340 with 11:1 or so compression, 93 octane may not be enough, ma need at least 100 octane to put into a performing motor potential.
 
joshua dewitt said:
factory 340 super big valve heads, suck and flow well for power, with the really high compression, the smaller port heads are more for torque and velocity, that will give you mileage. and factory 340 with 11:1 or so compression, 93 octane may not be enough, ma need at least 100 octane to put into a performing motor potential.
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I have 69 x heads stock valve size only thing done was valve job and hardened valve seats......
 
check your ignition timing, is your vaccum advance hose connected? were the jets rods and spring changed? low pressure on tires could cause a little bad mileage too but not too much
 
The factory 340 in 69 had 10.2:1 compression, not 11. In fact, it probably blueprinted a good bit lower. Probably around 9.5.
 
With 3.23 gears, I would say something is wrong. I have a 69 Barracuda FB with a mildly built 340 (about 375 HP), 4 spd, 235-60-14 tires, 750 Edelbrock carb and 3.55 gears. I normally get about 15 mpg when I drive to a car show.
 
Gonna throw a curve ball, here.... Seven carbureted circuits,and do you know them? If completely stock,a good tune up,and carb adjustment fixes all(still running points?). For the love of fighting sh*t,Buy a Persontrix ,or accel points conversion kit.???
 
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y2swinger69 said:
I just attended the 16 chryslers at carlisle and finally after 8k miles after beING restored I calculated mileage! First off I have a 69 dart with the numbers driveline. 340 stock 727 and 3.23 suregrip. I'm running a 255/60/15. I'm only averaging 10mpg running at 60mph. I feel that's poor mileage and was wondering what yall are getting. The car runs great but is there something going on with me achieving these numbers. I'm running 93 octane also. Thanks in advance
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69 swinger 340 4/spd. 3.91 gears 245/60/14. Combined mileage is right around 13 for me.
 
same story with my ride... getting 11 to 12 mpg on the highway... ( 20 l /100km ) 340 with x heads... 727 3.23 rear... carb doesn´t make a difference... 600 EDE 625 Carter or 800 cfm TQ allways the fuel consumtion
is nearly the same.
I thnik...the igition is the "secret ".... I am tinkering around since weeks with my Ignition curve... and allways...yes allways when I try to bring a vacuum advance into the game... the engine is pinging..under LIGHT LOAD ! at aprox. 2500 rpm....
Think the "problem " is the CR ... perhaps I will pull the heads..the verify the real CR...perhaps I can use a "THICKER " Headgasket...to compensate the high CR

Greetings Juergen
 
y2swinger69 said:
625 carter..... car doesn't run rich
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The fact that the plugs look clean is not an adequate indicator of 'not running rich' with the newer fuels. You can run AFR's in the 12-13 range and still have very clean looking plugs. But that AFR range is going to result in poor mileage.

By comparison, at 60 mph, my son's 340 with a Holley 675 is running 13-14 mpg at steady cruise; Crane Z268 cam, 10:1 SCR, AL heads, stock vacuum advance connected, 15 degrees initial timing. His 3.55 rear with a Gear Vendors OD is a final ratio of 2.95, so at most of that better mileage is in the carb tuning, not in the final drive ratio compared to your 3.23 rear gear. And that is with tuning that is not all that good for mileage; the AFR's are not up in the 15-16 range as they would be for a modest economy tune.

So I think you have a long way to go for cruise tuning.
 
brasil said:
same story with my ride... getting 11 to 12 mpg on the highway... ( 20 l /100km ) 340 with x heads... 727 3.23 rear... carb doesn´t make a difference... 600 EDE 625 Carter or 800 cfm TQ allways the fuel consumtion
is nearly the same.
I thnik...the igition is the "secret ".... I am tinkering around since weeks with my Ignition curve... and allways...yes allways when I try to bring a vacuum advance into the game... the engine is pinging..under LIGHT LOAD ! at aprox. 2500 rpm....
Think the "problem " is the CR ... perhaps I will pull the heads..the verify the real CR...perhaps I can use a "THICKER " Headgasket...to compensate the high CR

Greetings Juergen
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Juergen, I would not suspect high CR to be the problem unless it is 11:1 or higher and is really causing a large amount of retarding of the ignition timing. Higher CR's give better combustion efficiency. I have run 10+:1 SCR and had mileages in the 18-19 mpg range. And others here have done better. Most of the mileage issues are due to carb tuning, and due to the cams selected.
 
Just wondering if you were going by the odometer and if its accurate with the different rear tire?
 
340doc said:
Just wondering if you were going by the odometer and if its accurate with the different rear tire?
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Mileage wise I was but I should be able to go more then 150 miles on a tank especially of the secondaries never open...... Idk that's why I listed the rear tire size cause I knew that would factor in. But by how much?
 
If you are serious about tuning, get an A/F gauge. Unless you drive with your foot in the radiator all the time, 10 mpg is low, should be better regardless of tire size.

I drove my D100 to Carlisle from Long Island, 225 miles. It's about as aerodynamic as a brick. Has an over cammed, low compression 400 with a Holley 750, hi-rise intake headers into a single muffler, an NP435 truck trans, 15" SUV tires and 3.23 gears. On the way there, my mileage was 12.8 but I spent a lot of time in slow traffic.
 
Lack of vacuum advance. It's ping is probably related to a fuel curve issue. Getting control of the advance curve for a street car is also different than a race car or car with a high stall converter. All in at 2500 is not a good thing with a tight converter and slightly lean mixture. Slow the mechanical advance curve and or shorten it and make sure total timing with vacuum in not going over 45 degrees. You may need stiffer metering rod springs and or smaller rods too.
 
y2swinger69 said:
Mileage wise I was but I should be able to go more then 150 miles on a tank especially of the secondaries never open...... Idk that's why I listed the rear tire size cause I knew that would factor in. But by how much?
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I picked up 2 mpg once I corrected the miles but agree with others that its still low.
 
First verify your speedo is accurate. Then make sure your ignition advance curve is good and make sure your vacuum advance is working properly (if you don't have it you need it!!). Then go through your carb and make sure it is clean inside, no vacuum leaks, plugged passages, float height good etc. Once the carb is known to be in good shape then start playing around with metering rods and springs. If you don't have an O2 sensor with an AFR meter I'd highly recommend one; if you don't want to get one right now you can tune your carb 'trial and error', just swap metering rods or springs and test drive the car after each change and don't do more than one change at once. You basically want to lean the cruise circuit out more and more until you notice any surging at cruise then go back up a size or two richer on the rods/jets.
 
My truck does not like vacuum advance at all. I have a lot of initial advance because of the cam and used the FBO limiter plate to limit the mechanical. I don't remember what it's set at exactly but with V.A. hooked up it sputters bad. I adjusted the canister to where it was not as prevalent and maybe I can tweak it a little more but the symptoms still persisted so I capped it off. I gained mileage with my last round of tuning but I am not sure if I left anything on the table without the V.A.
 
Yeah your tuning has to be off. My duster has a 1990 360 with 9.7 compression, an air-gap manifold (not a mileage booster), Lunati Voodoo 270/279 hyd. roller cam, roller valvetrain on stock 308 heads, topped with a Eddy AVS 650 carb.
I also have an A999 (with lockup function fully removed), an 8.25 with 3.21 gears and a 27 inch tire.
I tuned my carb with an AFR gauge, I'm actually running a tad on the rich side.
I get anywhere from about 16.5 to 17.5mpg freeway mileage at around 70 mph
I also get about 10 to 14 around town (depending how froggy I get with the throttle).
 
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