"Decent" MPG out of a '69?

[billschroeder5842]

I'm wondering if I should do something different to get better gas milage out of my '69, or just be thankful that it runs well and is pretty dependable...

I just checked and I'm getting 12.5 mpg after a highway road trip. My '69 has a 383 with a light cam, A/C, headers, 3" exhaust, aluminum intake, electronic ignition and a Edlebrock performer. There is shift kit in the auto trans and a 3.23 rear end. I have 15" Cragars. Car runs well and fires right up.

Any ideas or should I leave well enough alone?

[greenpigs]

When was the car aligned last?
The tire pressure is good right?

12.5 mpg sounds a little low for mostly highway driving, what was your average speed?

Not sure how much it matters but what is your initial timing?

I have read that you want to be cruising in the meat of your engines torque curve. I don't know enough to give a clear answer but this is how sometimes guys have swapped from a 2.73 to a 3.23 gear and got better gas mileage. The swap moved motors RPM up to where the motor is making better torque and not "working" as hard to maintain the speed.

You could play around with rear tire diameter to lower your cruising RPM also if you think that would help.

[68X426]

12.5 is "well enough". But since you asked ......

One: air up the tires. No joke, it's obvious, and yet people run around with 20-22-24 psi and don't know it. Depending on your tire you can run 28 to 33.

Second, it's called "overdrive". Not cost effective if only done for mileage, but obvious improvement. http://www.dodgecharger.com/forum/index.php/topic,75209.0.html

[b5blue]

  How is the ignition set up? Are you running vacuum advance? It made a big difference for me "across the board" when I changed to an FBO set up dist. and A688 ignition kit. (Not that someone else couldn't do it just as well) 

[billschroeder5842]

29.5 on the front and 31.5 on the rear. My speed was about 70 on interstate 35 north of Ft worth.

Timing is about 12  initial and have no idea on total. I had a "helper" give me a pointer on timing the engine using a vacuum guage at about 2500 rpm. Sounds funny but the motor pulls about 20 psi and runs really smooth now throughout the range.

[greenpigs]

You should check your tires but most are 35 psi recommended pressure. Timing by max vacuum is the way I did it also, but I got 18 initial out of my combo. Everyones motor is different but taking it to 2500 rpm to get the max vacuum reading sounds excessive.

[Ghoste]

What do you mean by "light cam"?  I'm thinking with a few bolt on speed parts and a/c running down the highway at 70mph that 12.5 isn't too bad.

[moparjohn]

My 69 gets just under 14 mpg when i'm on the highway.

[elacruze]

Your carb tuning makes a huge difference. What carb do you have? If it's a Holley, it's easy to dump fuel needlessly if your accelerator pump shot is bigger than necessary, or if your power valve opens sooner than necessary. Keep in mind though, tuning for mileage will always cross swords with tuning for power sooner or later.

[Ghoste]

  Ain't that the truth?

[greenpigs]

I searched a little and see Bill is running an Eldelbrock, but did not see what size. With a little more info maybe someone here can help him out better.

[billschroeder5842]

I'm running an Edelbrok performer-not sure of the size This is my first Eddy as I've always had Holleys.

New alignenement although I'll Air up my tires to 35ish.

I do have a vacuum advance and it seems to operate well.

Light cam...I do have a cam in the car but it is not super agressive. I don't have the specs, but I've been around enough to know that the cam is is mild.

Hope this helps-thanks for your ideas!

[greenpigs]

  I am at work so I can't go check but I think the model number is stamped on the bottom front left side. should be something like 1411 ,1407 etc.

[ACUDANUT]

 IMO, be happy it runs great and just enjoy it....If your after economy, your in the wrong hobby....Or maybe, you should think about a slant 6. 

[HPP]

Gaining economy is about gaining efficiency. The best way to gain efficiency is to put in a leaner charge, squeeze it more tightly, and burn it more completely.

Leaner charge is achived through optimizing carb mixture through the range of operation. Not just curb idle or WOT, but differing cruise mods. This is where, IMO, an AFB is better than a Holley because it can be dialed in more precisely at part throttle and cruise mods.

Squeeze it more tightly is increasing compression. If your engine is already built, this opportunity is already gone, however, you can alter cam events and installation centerline to increase cylinder pressure.

Burn it more completely is using the best matched ignition curves delivering the hottest most reliable spark in the commonly used rpm range that your car cruises in.

Notice no where did I necessarily say spin the engine slower. Lower cruising rpm is great for motor longevity, but if your outside the sweet spot of the torque curve, can create an engine that is not as efficient as it may be in a higher rpm range. I'm also assuming your already looking at thing likes optimal alignment, proper tire pressure, and casual driving habits instead of lighting them off at every stop light.

[Ghoste]

You bring up an interesting point.  When I switched to the 4:10 in my car, the fuel mileage suffered only very slightly if at all under NORMAL cruising conditions because it brought the engine into that sweet zone you mention as far as the camshaft and overall efficiency were concerned.

[elacruze]

I really think you should be getting better mileage. You don't have a lot of gear, and a 'light' cam won't necessarily reduce mileage. Got headers?
Just a WAG without specifics on your combination, I'd say that you could use more total timing and perhaps lean out the carb some. If it was lean you'd notice a bog while opening throttle, or acceleration while reducing throttle. I'd expect your timing to be something like 8 base, 32 advanced and 42 total with vacuum.

I get ~20mpg with my 318-2 pickup with 3.55:1 gears. You should be able to do better than 12.

[flyinlow]

I get about 18 mpg on the road with a 73 /440/A518/ 3.55. The OD helped about 2-3 mpg (2000 rpm @70 mph) The thermoquad gets the best milage 16:1 A/F ratio at cruise, the eddy 800 performer with leaned out primary rods is about 1mpg less. The Holley 750 gets about 2mpg less of course. 36* centriifical advance with limited vacuum advance.

[TylerCharger69]

1969 Dodge Charger.....I'm not concerned about mileage.   But for what it's worth.....I get about 12 or 13 MPG

[MedPhys]

This is probably more than you are willing to do, but this is the route that I will be taking:

Replace current intake with one of the new EFI intakes.  Run a megasquirt 3.  You will be able to run sequential spark(if you add a coil pack per cylinder), sequential injection, and two WBo2 sensors.  Not to mention tuning your fuel and spark table via laptop. I'm sure mileage will pick up significantly when your only delivering fuel to the cylinder that needs it, and tuning a proper AFR.  The MAP sensor adjusts fuel for different MAP readings, and IAT adjust fuel for temp changes.  You set an AFR target table, so it is constantly adjusting fuel to reach target.  I'm running one on another project and it is great.

[Kern Dog]

I made a 900 mile round trip from for the LA Spring Fling  a few weeks ago and I averaged 11 mpg. My combo: 440/493 with 10.8 squeeze, Edelbrock 84 cc heads, MP '509 cam, Performer RPM intake, Demon 850 carb with 85/93 jets and a 3.5 power valve, 2" TTI headers and electronic ignition. 727 with a 3000 stall converer. I switched the 3.23 gears in for the trip. I know that if I used a well tuned ThermoQuad, I could possibly get 14 or 15. More spark lead could help too, but the cat piss CA gas wont let me run more than 31 degrees of advance.