improved MPG

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DaDa102250

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Inherited 77Chev 1/2 ton w/350 4bbl 4speed. G-paw bought it to pull 5th wheel cattle trailer. can pull a stump in 1st gear but MPG is terrible. Pull Bumper hitch trailer from time to time, 5th wheel once in a blue moon. hate to give up pulling power but would like to improve MPG. EFI, TBI, Upgrade trans to 5 spd? combination of intakes and trans? suggestions?
 

1987 GMC Jimmy

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Start simple. Tire pressure good?Brakes aren’t dragging? Tuneup (plugs, cap, rotor, fuel filter, and plug wires if needed) done? These are easy places to recoup performance and economy. Factory carb? If yes, good. If not, I’d make that my first stop. Do you know the gearing? He may have put shorter gears in it since it was intended as a towing rig. I know my dad did the opposite when he didn’t need to as much or as heavy loads. The truck has always done 98% highway driving, and there was a noticeable improvement in economy. You can check the SPID/RPO sticker in the glovebox, and it’ll tell you what it came with. That year should have each code elaborated, but if not, the code should be GU*. The gearing on that SM465 is not the best in terms of economy, but it’s such a good gearbox, that I wouldn’t run to throw it away just yet. You’re in AL so I’d throw away some emissions junk. If it has a smog pump, that can go. If it still has a cat or cats, it/they can go, and you can also consider switching to headers. Nothing else under there is going to rob you of anything. If it has a thermal fan clutch, great. If it has anything else, especially a flex fan, chunk it and do a thermal clutch. I would try everything I could on the outside before I started getting really serious with heads, cam, intake, and gearbox. It sounds like the NV4500 has caught your eye, but I’d try everything else before investing the time and money. I like your town, by the way. I’ve got an old high school roommate at UAH, and I actually used to live a few hours from there in Columbus, MS so I was there quite a few times for school and what not.
 

rt66paul

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Sometimes it is as easy as installing new spark plugs that have a proper gap.
 

DaDa102250

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Thanks for the info. found sticker. Rear end 3.40. All it says about tranny is 4 spd. man. option # M20. will do some more digging on trans. if anyone knows about m20 option let me know. haven't found any thing yet. found out that a new 350 4bolt main was installed awhile back and the truck sat off and on for several years. according to family friend it has less than 3 thou mi on it.
 

legopnuematic

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SM465 is the only non overdrive 4 speed put in these trucks. I agree with the above that a good tune up is the best place to start at.
 

rpcraft

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if you want better mpg's buy a honda civic. Your'e driving a brick shaped truck that weighs a ccouple tons and is made to tow and pull. Even with a modern EFI system and OD trans you would at best average 17 mpg or so, less if you drive in town or tow any. Do a tune-up, put spend a little money on some power upgrades, and that is probably the best you can hope for overall, and then enjoy your square for what it is.
 

dvdswan

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After a tune up, invest in a vacuum gauge. Keeping you vacuum at or close to 20 while at cruise will help. In other words, keep you foot off the gas or be light with it. I have a 4 sp, 3.08 gears and 33s its a slug so to speak but I average 15-17. Even upgrading you engine, trans, gears, etc. you will be lucky to get close to 20, if you lucky. As said above, you're moving a brick down the road that is a heavy beast.
 

CSFJ

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I had a '79 k10 in high school, and for a few years after. 350 engine, th350 trans, 3.42 axle gears, 31x10.50 tires. The trans had the same 1:1 final drive ratio as yours. I saw 12mpg on a good day. As stated above, if mileage is a concern, buy something that gets better mpg for a commuter, and leave the truck alone. Save it for when you need a truck, or just want to enjoy it.
 

Honky Kong jr

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Kinda ironic there was s 101 of these milage threads and all answers are the same, yet they still pop up like herpes in a trailer park. Isn’t there a cream or sav for these things or is this just forum herpes and they will never go away????
 

436'd skylark

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I get 17 with my 77 camper special. It also has a duramax and an allision though.

With a proper tune you should see mid to low teens. You have to drive easy though.
 

rpcraft

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My answer to people asking about mpg's is to point out that if you want to really gripe about mpg's put your tcase in low and see how fast you can plow through 30 gallons of fuel offroad.
 

Rusty Nail

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Kinda ironic there was s 101 of these milage threads and all answers are the same, yet they still pop up like herpes in a trailer park. Isn’t there a cream or sav for these things or is this just forum herpes and they will never go away????


Nuckin Foobz! I thought there was a rule against posting? Until you've been here five days or something?

FORUM HERPES!!!!

Sliek omg. My 40 year old steel truk has teh chitty mpgeez compared to mah new Focus!! **** can I do?????????
 
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Dub11

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if you want better mpg's buy a honda civic. Your'e driving a brick shaped truck that weighs a ccouple tons and is made to tow and pull. Even with a modern EFI system and OD trans you would at best average 17 mpg or so, less if you drive in town or tow any. Do a tune-up, put spend a little money on some power upgrades, and that is probably the best you can hope for overall, and then enjoy your square for what it is.

That's my plan of attack lol.
 

rpcraft

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I remember back when I had my 77 Jimmy I was making about 7 to 8 bucks an hour and I think that was around 1995 or so. I drove for a long time not really thinking too much about the price of fuel other than I had a schedule that afforded me the opportunity to fill it up about once every two weeks (and that was with the 30 gallon tank). Then I remember some time around 1999 gas hit around 1.30 a gallon (I think) and I remember thinking I was never going to be able to afford a full tank of gas again. Funny how you gain perspective over time. Then again it's been about 4 weeks since I had to put gas in my current daily truck, and that comes with the expense of having to fly out at the airport and live out of a hotel all week long... I'd gladly go back to filling that tank up weekly at 1.30 than having to fly around and work, lol. Funny how time adds perspective. I think once I get my Jimmy Ls swap done and finish doing all the accutruments I'm going to pull a John Madden and let the company pay for my fuel again.
 

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