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Discussion Starter · #1 ·
I just bought an 85 Jimmy last week on ebay. I am waiting for it to be shipped here from California. I got a great deal on it. It is in great mechanical shape with no rust. It only needs a little interior work. I was really excited about it until gas prices spiked this week. I am not going to be doing any off roading and I will be doing about 90% of my driving on the highway. I was driving a 96 s-10 with the 4.3 high output. I was getting about 20mpg. I decided to buy the Jimmy because I got tired of having a vehicle I can't work on because of the computer system. Besides that, the 2wd doesn't do too well in the snow even with 500 pounds of sand in the back and the ABS system has been acting up. Two trips to the dealership and the brakes still lock up on ice, sand, and snow.

I drive about 300 miles a week to and from school. I am working my way through college and I don't have a lot of extra money to waste on gas. I am making a little money by selling my truck and I am trying to find ways to increase the fuel economy on the Jimmy.

It has a freshly rebuilt 305 with 1000 miles on it and about 500 on a rebuilt tranny. It is all stock with 32x265x15 tires. I am thinking about doing some of the following: Narrower tires (it needs new tires anyway), carb spacer, upgraded exhaust, upgrade the distributor/ignition, upgrade air filter/air intake system.

Any suggestions on what would give me the best bang for my buck and what things would make no difference? I would love to keep the Jimmy but if I can't get better than 15 mpg I will have to sell it and keep my S-10. I know that the mileage will be no where near as good as it was with my truck but I would like to try to boost it a little. I am afraid of what it will cost to feed this thing during the summer when gas is $2.25 a gallon. If I have to spend too much on gas for the Jimmy, I won't have any cash left to work on my Camaro!! Thanks!!!
 

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First, I'm glad you went ahead and got the Blazer!!

Pump the tires up on it or put smooth radial street tires on it that roll better.

Tune it COMPLETELY up and drive her easy is about it I am afraid, short of dropping a V-6 or a 250-straight-6 in it..

My '80, Chevy C/10 1/2 ton has a 250-6 in it and now a 4-speed stick on the floor as well as 2.76 rearend gears AND I think that is about as good as it gets!! I'm sorry but I don't know it's mileage yet???

I think Travis said one he had like mine got like 22 mpg on the road if not mistaken??

I will say that my B-I-L's old '77 Gimmy h-d 3/4 ton 4x4 with a 350/Granny tranny gets like 8 mpg EMPTY OR LOADED!!

And my old RR Buddy had one and he put my original 350 motor's wore-out Q-Jet on his and his mileage jumped from 8 to 12!!

But these two aren't Blazers...

pdq67
 

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My truck is a '86 C10 with a 350, TH350C, and 3.23 gears. I get 17MPG on a 70MPH cruise. Here's what I've done:

Perf. Intake
Tune Qjet with LM-1 wideband sensor (big difference!)
Bowl blend heads
Add 2nd cold air snorkel
K&N filter
Dual exhaust

I wouldn't bother with an upgraded ignition system. The HEI is excellent and is hard to improve on for a factory motor.

The LM-1 from Innovative Motorsports was the ticket. You can tune your carb with precision, and this really helped me get more miliage.

Hopefully yours still has the factory air box. Usually the filter size is a 12x3 or so filter, but you can go to the junkyard and find the tall air cleaner lid that will allow you to install a 12x6 filter, and grab one more snorkel and add it onto your factory box. This was about 1MPG on my truck.
 

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My bad I saw the 85 Jimmy and had nightmare flashback about my old S-15 Jimmy with the 2.8 V6
 

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Discussion Starter · #6 ·
Originally posted by Silver69Camaro:
My truck is a '86 C10 with a 350, TH350C, and 3.23 gears. I get 17MPG on a 70MPH cruise. Here's what I've done:

Perf. Intake
Tune Qjet with LM-1 wideband sensor (big difference!)
Bowl blend heads
Add 2nd cold air snorkel
K&N filter
Dual exhaust


The LM-1 from Innovative Motorsports was the ticket. You can tune your carb with precision, and this really helped me get more miliage.

Hopefully yours still has the factory air box. Usually the filter size is a 12x3 or so filter, but you can go to the junkyard and find the tall air cleaner lid that will allow you to install a 12x6 filter, and grab one more snorkel and add it onto your factory box. This was about 1MPG on my truck.
Interesting ideas. Can you tell me a little more about this LM-1? That is new to me. How did you add the second snorkel?

I am hoping that having the 700-r4 tranny will help out because of the overdrive. It also has lock outs on the front. What about pulling the 3.73 and going to a higher gear to lower the RPM at cruising speeds? I haven't done any work on a 4wd... do I have to adjust the front axle too?

Thanks for the ideas and the support guys!
 

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convert the engine and differentials to synthetic oils and gear lubes, that will gain you instant mileage with less friction.
My 97Tahoe 350 gets over 21 on the highway now.
 

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I was getting 17mpg in a suburban with 3.73's and relatively short tires.

I had full length headers and dual exhaust.
Synthetic oil
OD transmission.

The OD will give you the most boost in mileage.
The exhaust system will be the next best bang for the buck.
The oil is questionable. I didn't notice any improvement in my new suburban with synthetic oil.

I tore the exhaust system off my cavalier and gained 3MPG. The exhaust system is where the extra, cheap MPG improvement is. Adding a 700R4 is relatively expensive and takes a while to recoup the gas savings.
 

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With the 700R4 the 3.73 gears should be fine. It's a heavy vehicle so going down would make it harder to get moving and waste gas. Make sure it has a decent exhaust system and look at replacing the distributor, coil and wires with high performance stuff. I put in a GMPP distributor, Hypertech coil(which has the highest voltage) and MSD wires, regapped the plugs a little wider and I picked up 1 mpg on my 454. The GM HEI is good, but it has a lame curve and the voltage is pretty low. When you get new tires go down to 31x10.5x15 to reduce rolling resistance. But doing all these mods will cost some money and you have to look at how long will it take you to recoup the cost in gas savings. An 85 Jimmy really isn't the best choice for the amount of driving you're doing.
 
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