Best possible mileage?

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89on35s

Inferno Red Duster
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I am thinking about buying an 84 Dodge Short bed 2wd Dodge pick up with a 225, 4spd O.D. standard trans and whatever rear gear ratio that it would have come with. I am willing to optimize whatever I need in an effort to maximize highway mileage.
What type of mileage is this thing capable of? What could be done to make it the best it can be? I am new to slants, as I only ever had an 81 Diplomat with a 225 many years ago.

Cley
 
Oh and the 225 is a fresh rebuild by a the owner who is a machinist and very good mechanic.

Cley
 
i got an 80 model short step bed D150 stock /6 4 speed od truck, my daily driver, gets 18 mpg around town and bout the same at 65+ on hwy, but bout 22 mpg cruising the back roads at 45 to 55!! and that not even trying!! no idea how its timed, ant ever run over head, ant ever pulled the plugs, thing just keeps going, out run the energizer bunny!!
 
i used to get 22mpg out of my 69 vert barracuda 318 2bbl 4speed back in the 80s. my current dart is only getting 10 city 13 hwy right now. pretty bad mpg comparatively. i will be working on mpg this summer for sure.
 
My 83 slant powered short bed D150, a833 OD transmission with 3:73 gears will get 15 mpg in every day city stop and go driving. On the highway, keep the speed at 65 or below it will get in the low 20’s mpg. Push it it to 75 and above and the mpg will drop to the 17’s. I could probably get better milage numbers, as I don’t drive this truck ez.
The 80’s D150’s are great trucks, but they are also heavy and as aerodynamic as a brick.
About anything on the road today will get substantially better mileage. To get the best mileage keep the tires properly inflated and drive it with a light foot on the throttle.
 
i had the performance vacuum gauge in the 69 i used to get a kick out of keeping the vacuum as high as i could. for mileage
 
I had a 225/4-speed with 3.91 gears in a '74 D100. I got 24-26 mpg. Unbelievable, but we checked it several times.
 
my 2000 lwb conversion van with efi 5.2 magnum is getting 16mpg and weighs probably 2k lbs more than the 71 dart so surely the dart can improve
 
Dart Lite/Feather Duster claimed mid 30's with a slant: lean carb and a reworked distributor.
 
Take all the smog stuff off, lean burn if it’s got it. Recurve the distributor and get as much vacuum advance you can get Before she pings. If you want to do deeper up the compression by milling the cylinder head down etc. I get 22 mpg with my 64 dart 4 speed headers four barrel with 3.55 gears!
 
I had a 83 Dodge pick up slant six OD 4 speed. Never really checked the mileage but did my ritual comute every week and only had to fill up once a week with Premium. On regular I would have to gas up sooner so for whatever reason I got more miles per tank with super.
 
I believe 3.55 is the "standard" gear, but there were others. In general, about as good as they will get is "around" 20 give or take. That's pretty good for a truck. Honestly, a 318 would probably get better with more power, but the cool points go to the slant six.
 
I kept careful notes on my 1969 Dart 225 which I owned 1976 until 1994 (stolen). I got 22 mpg highway, but the speed limit was 55 mph back then. Around 1988 I changed to electronic ignition (Crane Cams XR700), but noticed no difference from the points. The Holley 1920 carb was always finicky, running too lean at idle. Might have done better with larger OD tires.
 
LMAO!

How about that guy, he loved the “Plastic Fantastic” TQ carb, dang, his screen name escapes me at the moment.

Any ways.... claimed 42 MPG’s with a TQ. 53+ on his slant 6. No overdrive.... Swears Chrysler had literature on the subject out circulating in print.
 
My buddies 340 six pac got better gas mileage than my /6 I had in my 65 Dart. I would get about 18-20 on the Highway.
 
I believe 3.55 is the "standard" gear, but there were others. In general, about as good as they will get is "around" 20 give or take. That's pretty good for a truck. Honestly, a 318 would probably get better with more power, but the cool points go to the slant six.
My old 93 Dakota w od only got 18
 
What type of mileage is this thing capable of? What could be done to make it the best it can be?
Martinsville..... yur only 8.5 hours from me.
As to the engine; Do this:
Get the thing tuned up and running right. Put a 195 stat in it.If it overheats fix it, but make it work with the 195 stat. If it has flat tappets, set them at that temp to .013/.022.
Next; you have to make sure the engine gets the maximum amount of CRUISE-Timing possible, that it tells you it WANTS, not what you might think it wants.
So, Make sure the V-can is working.
IMO, you can leave all the pollution junk on there for now. If it has a lean-burn, make sure the Vacuum pod is functioning. Make sure the Vcan works in Neutral.
Ok next you will need a timing lite and a tachometer.
I'm guessing your combo will cruise at or near 65= 2200.
So at running temperature; in neutral, put it up on the fast idle cam at around 2200 rpm. Then just pull in timing until it stops picking up rpm; don't even put the lite on yet. Then reduce the rpm back to 2200. Next, RETARD the timing some until the rpm peaks again. But if the engine loses rpm, then advance it again, until it stops picking up rpm. And repeat until you find the max timing that makes 2200 rpm.
When the rpm peaks at around 2200 rpm NOW read the timing.
Then retard it three degrees and write the number down. Then return the engine to idle.
Now, if you run outta slot on the distributor before the rpm peaks; modify the slots! for more advance. How will you know ? IDK, I'll guess your slanty will TOLERATE about 42* or more at 2200 in Neutral.
What you have just done, is obtain the maximum advance that your particular combo, WANTS or TOLERATES, at 2200rpm.
Now you just gotta figure out how to make it happen. ( A new post or thread)

As to the chassis:
It is a brick!
I got an 84 with a 318, and the faster I drive it the more gas it sucks....... cuz it has to punch a pretty big hole in the air. So you can't do much about that. But there are some things you can do.
> Hard tire pressures as mentioned
> alignment
> make sure brakes are not dragging and wheelbearing grease ain't turned to soap.
> install new U-joints and repack them before installing, with Moly grease
Install 75/90Gear oil in the rear and STRAIGHT Dextron-II in the trans.
> some say leave the tailgate at home.
> turn the A/C off, keep the windows rolled up. If you have to make a choice, use the A/C
> that's about all I can think of. There are more things you can do, but none are cheap. These will get to to 80 or 90%

Once you have this baselined, then you can map out your timing curves, and see if there's a lil more left in the tune.
Or I'll sell you my 84 and you can steal parts,lol.
 
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I run a tonneau on my F150 and keep my tailgate. It’s very economical. I don’t go anywhere. Poor truck just kinda sets there. It was a little whiter today.

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