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mpg

J

John

Basic User
I'm preasently getting around 10 mpg. the 83,8 is tuned to specks. I don't believe this is the normal range. It has the stock 258 5 speed w/ carter carb all else is stock. Can anyone coment?
 
I was only getting around 10 mpg in my stock 83 w/ 258, 5 speed and Carter carb. EPA fuel economy data says that it should be getting 17 to 21 mpg, but I've never saw those numbers out of mine. I was expecting the mileage to worsen with my 4 in. lift and 33's but it stayed about the same.

I just don't like the Carter Carb, even my new one (reman) gave me fits. It's a good place to start when trying to improve mileage.

I am in the process of installing an Edlebrock intake, Holley 2BBL carb and headers (from a wrecked CJ5), no numbers yet on the new mileage, I hope it doesn't get any worse...

Obviously, fuel injection is the way to go for definite mileage improvements when money is no object. I hear 15-17 mpg (a +30% improvement over 10 mpg) is quite common with the Howell and Mopar kits, but $1,200-$2,000 buys alot of gas when you're talking about a 5 mpg increase. It would take a few years for the fuel savings to pay for the parts.

Reading over this message, I realize I haven't been very helpful, I guess I am just commiserating with you! Good luck...
 
That seems low.

I have the a 258 with MPI, T-176 (i.e., no overdrive), 31" tires and the 2.73 hubs (I don't rockcrawl). I get ~18 mpg highway with the MOPAR Fuel Injection.

I use 87 octane (no pinging, then again Illinois doesn't have hills that would cause pinging). Also for those not familiar with Illinois fuel, all fuel here is required by law to have:
- 10% ethanol, and
- clean-air additives.
Those two items give me 2-4 mpg less vs. other states I've lived in. I and friends visiting from out of state have found this same mpg variance on a variety of different makes and models of cars and trucks.

Hope this helps,
Jim

P.S. The 10% ethanol requirement keeps folks at ADM (Archer Daniels Midland) employeed and provides a production incentive for corn growers.
 
10 is low in my opinion. I had an 83 Cherokee, full sized, with the 258, 4 spd and 3.31 gears and 31 inch tires and got a solid 20-22 on the highway when new and averaged (all uses) almost 17 for the 160k miles we owned it, it went up when I went to 4.10s and 33s, even after I added a winch, roll cage, blah blah and still could hit a solid 17 on the highway. My son's first scrambler would get 17ish on the highway at 55-60 with the 258 five speed and 4.10s with 33s, his scrambler now witha full hardtop, 4.10s and 33s and a 4 spd only gets about 14, but it runs like crap. I'm hoping that a good tune, some minor carb work (like a good cleaning) and my old Jacobs ignition will bump it back up to the high teens.

All that aside, mileage is a function of many things, driving style is paramount as is good tune and overall condition of vehicle. The aerodynamics are pretty fixed but tire pressure can be adjusted, timing can be slightly advanced from stock, ignition can be optimized, plug gap, etc. I've seen 2-3 mpg from simply changing plugs. Use is also a huge player, if you are an urban cummuter with lots of stop and go your mileage will be pretty poor regardless when compared to steady state highway driving. Case in point: I just sold my 74 cj 5, 304, projection, t 18, 4.27s detroits, 35" swampers, etc. A rolling brick aerodynamically, and heavy. I got 10-11 around town, I got 14ish enroute to Moab this year at 55-60 mph, at 70-75 it'll drop back to about 10-11. With 33s on it I could do 15-16 at a steady 60-65mph. So if your commute is urban or if you live at any significant altitude advance your timing (~ 2 degrees per 1000 ft) slightly, maybe go a range hotter in plugs if your driving is short urban type, open the gap up on the plugs a little, more if you go to a jacobs or a TFI/HEI mod and see what happens. Of course run the tires a little on the hard side, and drive conservatively.

good luck!

tr
 
I really cannot comment on the 258 but I had the rinky dink 251 Iron Duke....which got a consistent 10 mpg. It finally took its last breath about 2 years ago so I put in a chevy 350...which oddly enough got 10 - 12 mpg. We moved from MN to CO and the elevation was killing my rig (not to mention some other problems). So I had Jim (Pro4X4 in Aurora) install a Howell fuel injection kit and some other items...not motor related. WOW. I now get 18 - 20 mph. driving up and down big hills....cruising at around 65- 70 mph. By the way if any of you are interested in getting this done (and you live in or near Denver, I would higly recommend Jim....he is amazing!!!!

my .02

-KElly
 
Get rid of the Carter

John,
Get rid of the Carter! It wont even make a good boat anchor.
Go with either a Weber 32/36,if your engine is stock, or a repl-
acement intake,Offy or Clifford,and a small 4 bbl.Your best bet
for mpg will be the Weber.I have a souped up 258,(headers,
cam,MSD,Offy and Edelbrock 4 bbl. etc.) and I get 17+ mpg.I run
31" tires and 2.73's.I'd trade a couple o' mpg's for some mid 3'
gears.The Weber will run $375.00 or a little more but it's a com-
plete kit.The 4 bbl setup will run $600.00 or more a takes minor
fabrication.Whatever you decide if I acn be of help let me know.
Good Luck,Good Jeepin' and God Bless.
 
I ran a weber 32/36 for a while, averaged 16 mpg. Replaced it with a motorcraft 2100 off a ford van, now get about 18 mpg. This is with 33 X 12.5s, and 3.73 gears. I also did the math to convert it to true miles. Oh yeah, GM HEI from a nova. BIG difference. Alan.
 
MPG

I got 16 going about 60 on the highway and I have 35" tires and 4.56 gears. The 5 speed probably helps though. My 258 is rebuilt though but still has the original carter carb. I've also yanked all the smog crap off including a new exhaust with out the catalytic converter. Before I was running 33" tires and 3.31 gears and got as high as 18 mpg so I dont know what your problem is with your engine????
 
with my slowly going southward 258 and 32/36 weber carb 3.73 gears 32 (probably 31-30.5 actually) tires, heavy duty bumpers and roll cage i get about 18-20 on the highway and about 23 if i get a semi that i can tail going about 70. I think a lot has to do with the carter carb, my friends 258 with 29in tires, 2.73's (maybe a little lower bust still pretty high axle gears) got about 13 mpg, now he has a beefed up 360 with a t-5 (same tranny as with his 6banger) and gets 19 mpg if he isnt standing on it.
 
When i first got my scrambler and it was all stock, i think i got around 16 or 17 mpg.

Now with the 35's, 4:10's and Holly Projection ,(and lots more weight with all the other stuff), i think i get around 12 or 13.

I would agree with the other comment, get rid of your Carter carb.
 
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