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Best fuel milage setup???

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chrisquested

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Ok so i was sitting here thinking about having a nice k5 blazer 4x4 that looks good and i could use as a daily driver and still have it as a 4x4 for the beach and lake......

The blazer is going to have a 6 inch lift and 36 inch tires.

So i was thinking 350 motor/700r4 trans/np208 t case.

As for the axles i dont know what gearing to go with.

Trying to figure out how to get the best fuel mileage....
 
fuel mileage and 6" lifts with 36" tires is kinda like a "best case scenerio". do you plan to drive this on the highway? 4" lift and 35's would work just fine if you really want that "look" and not have to spend lots of money for parts......such as steering, drive shafts, axles, etc.........4.56's would be a good gear for 36" tires and a 700R4. perfect for 35". 4" also rides better too.

a 3" lift and 33's makes for a damned fine truck, less complicated and less drag....fwiw
 
Oh sorry i forgo its not gona be a 6 inch lift....It will be a 4 inch lift....Shackle flip in rear and 6 inch super lift front springs with a leaf taken out and the tires are 36 inch/12.50/16.50.

My blazer has 350 motor/350 trans/np203 t case.... I dont know what gears i got right now.

But i would be looking to get the best fuel milage....Right now i am thinking 350 motor/700r4 trans/np208 t case.

the motor will be all stock as it came from factory unless i can add somthing to get better fuel milage maybe a k&n cold air intake? it already has duel exhaust.
 
If you want to keep the 350 and 700r4 (I thought it sounded more like you were shopping), 4.10's or 4.56's will give the best economy. I wouldn't hope for more than 14-15 mpg highway.

The 6.2L diesel was pretty common in 80's Blazers, and 18-22 mpg seems to be fairly common. It's no powerhouse but isn't far behind in horsepower compared to a gas V8 of the same era and similar low end torque. Basically a motor built for mileage rather than power, they push a stock K5 around ok.
 
You are really not going to get that good a mileage from a truck like that.

Off road tires have more rolling resistance, the lift will increase the drag.

At the very minimum you will need to match you gears to your tire size.

I would say 4.88s or even 5.13s for 36s or 37s (most 37s actually measure 36).

Driving style is going to be important. Drive like a granny, truck gets better mileage. Simple as that. Use the brakes as little as possible, accelerate very slowly.

Now onto actual mods to increase milage. You already have an overdrive trans and a 350 so sticking with those. You need to make sure both are in absolute peak operating performance. Synthetic fluids all the way around will help just a bit. Some HP mods can help too. Headers better ignition system, better exhaust, electric fan, fuel injection if you aren't already, if you are a new chip.

I would not expect much more than 15 though.

I have a 6.2 diesel blazer that runs pretty good but has crappy gears (3.42s) a 6" lift and a 700 that was on its way out. When I drove it home (which was erratic at best to help with the massive vibration it had) I got just under 20 mpg. I filled the tank the same way (waited at least 30 sec before topping off, 5 times) and the mileage came from mapquest.

My goal is to get 21 mpg reliably with 37s,
 
You REALLY need to find out what gears you have, if they aren't deep enough you won't help your fuel economy. You will burn up that 700R4 in relatively short order though.

If they're stock from a 70's Blazer, 3.73 is likely, but maybe higher. Not nearly deep enough for your tire size, for a 700R4.

The cost of new gears, a new trans, etc will FAR outweigh the cost of some fuel.

How much do you drive the truck?
 
38377k5 said:
You REALLY need to find out what gears you have, if they aren't deep enough you won't help your fuel economy. You will burn up that 700R4 in relatively short order though.

If they're stock from a 70's Blazer, 3.73 is likely, but maybe higher. Not nearly deep enough for your tire size, for a 700R4.

The cost of new gears, a new trans, etc will FAR outweigh the cost of some fuel.

How much do you drive the truck?
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I was going to make the blazer my dd and turn my 1980 chevy luv into my toy.....So i would end up driving this k5 as a dd.....So i was hoping to get 14-17 mpg if possible.

And the 350 turbo trans is an overdrive trans??? i thought the 700r4 was the only overdrive trans? My blazer is a 1975 k5 blazer 4x4.
 
chrisquested said:
I was going to make the blazer my dd and turn my 1980 chevy luv into my toy.....So i would end up driving this k5 as a dd.....So i was hoping to get 14-17 mpg if possible.

And the 350 turbo trans is an overdrive trans??? i thought the 700r4 was the only overdrive trans? My blazer is a 1975 k5 blazer 4x4.
Click to expand...

TH350 is a 3 speed, non OD trans

TH700R4 is a 4 speed, OD trans, more weak points but generally similar in design.

I honestly don't think 17 mpg is possible with a lifted K5 on 36's with a gas motor, maybe with a 6.2L diesel and OD trans. The lift and bigger tires make all of that worse.

To help fuel economy the best bang for your buck will be a part time kit in the t-case and switching to manual hubs in the front. It may take a bit to offset the cost of that, even though it's relatively cheap.
 
38377k5 said:
.I honestly don't think 17 mpg is possible with a lifted K5 on 36's with a gas motor, maybe with a 6.2L diesel and OD trans. The lift and bigger tires make all of that worse.
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I agree. I've got a similar setup with a manual overdrive trans (which is more efficient than the auto trans). 35" radial AT tires, 4" lift, and fuel injected 350.

If I drive it perfectly on the freeway, have the wind at my back, and have a small downhill grade, I can get 13mpg, if I round the number up from 12.5. Most other times it just gets 11.

You'll save more money by getting a Honda/Toyota than trying to squeeze any extra efficiency out of a truck like that with gears, tires, etc.
 
I have a 350 / Turbo 350 / 3.73 / 6in lift / 35.12.50 swampers = get right about 12 MPG on highway at 65mph running 2300-2400 RPM
 
One of my lost posts was on this thread. I will shorten it

My 73 blazer in all its forms (35s/3.73; 38s/4.10; 40s/4.56) with no lift and 35s and inbetween 6-8" with the rest.

I pretty much got 10 mpg all the time, with the 40s I had to keep it under or around 65 to get 10 but thats what I got.

Buddy with a 74 changed to a 700/208 4.56 gears in stock axles 4" lift and 35s newer motor mostly stock build but nice ignition exhaust and injected. Best he got was 13 on the highway.
 
This post got me curious as to how you find out how many mpg you get on an old truck ....I found this:

To find out your actual gas mileage, you just need to do some simple mathematics.
  1. Fill up your truck with gas, and write down your odometer reading.
  2. Drive like normal.
  3. Next time you need gas, pull up to the gas station and write down how many miles you’ve driven since you last filled up.
  4. Fill up your truck, and write down how many gallons o’ gasoline it took.
  5. To find your truck's MPG, divide your miles driven by gallons of gas.
However...one's fuel gauge would need to work properly...mine doesn't.
 
Chief Brody said:
However...one's fuel gauge would need to work properly...mine doesn't.
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The gauge doesn't need to work as long as you fill it up all the way both times. Your odometer is the thing that needs to be accurate. If you changed tire sizes or gear ratios, than the speedo needs to be re-calibrated for the change.
 
bp71k5 said:
The gauge doesn't need to work as long as you fill it up all the way both times. Your odometer is the thing that needs to be accurate. If you changed tire sizes or gear ratios, than the speedo needs to be re-calibrated for the change.
Click to expand...


When I calculate I typically use my GPS for miles. Alot more accurate.
 
blazinzuk said:
When I calculate I typically use my GPS for miles. Alot more accurate.
Click to expand...
I agree, even some stock vehicles speedometer and odometers are off, my old '86 was off by approximately 10%... For every mile I drove it registered 9/10 of a mile. So even though it only had recorded 146,000 miles when I sold it, it actually had closer to 161,000 miles!!! The easiest way to verify your speed and odometer accuracy is like blazinuk said, borrow a GPS unit. It also helped explain why at 60 mph on my speedometer I was blowing everyones doors off on the highway... I was actually doing about 67 mph in a 55. Saved me from getting a ticket, here in Pennsylvania they'll bust you for 7 mph over...
Back on topic, if I were you, I'd start by doing a good tuneup and see how this things running. Wouldn't hurt to do some maintenance in light of your post about the hubs, and knowing your cousin used to beat on it... Does it use any oil or coolant? Even just pulling and checking the spark plugs wouldn't hurt, how your plugs look can tell a lot of how a motors running. Most Haines and Chukchi Manuals have a nice color chart to compar your plugs with.
 
Everyone is looking at squeezing milage out of their rigs these days. Best advice, as is being stated, is to get your current rig running as best you can, and then set realistic expectations for what a old, brick shapped, v8 powered rig can do.

I've gone round in round in my mind-and on here- and basically changing your drive train all around for maybe a couple extra mpgs just isn't worth it.

If you need a truck- like I do, expect less than awesome milage. If you don't have to have one for a DD- get a car or a motorcycle.
 
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