Need some real numbers, MPG...

[83GMCK2500]

I have been following a few peoples' build threads and I am looking for some good solid numbers on economy. I'm talking daily driven, mixed, hwy, city, anything. Also, how the truck and engine is configured. I have an '83 4x4 3/4Ton and it will be getting an LQ4 and an NV4500, might even regrear it from 4.10 to 3.73. I am trying to estimate what my economy will be. My intent is to inject it with a 4bbl manifold drilled for injectors, and an air-only throttle body on it. Maybe a mild cam, looking at the SDPC HT1 cam. Specs: HERE Also, LQ9 flat top pistons are a possibility.

I am sure, going from the old carb'd 400sbc to an LS will be a big change and there will be a period of time when the skinny pedal gets a workout, but I am really interested in what kind of economy these engines are getting in our old iron.

[clinebarger]

I get 17 mpg average on my C20 Burb with a 5.3/4L60E, 6.0L & yours being 4x4 will be lower, Im guessing around 13-14mpg as a realistic average.

[Daves70]

I'm in the process also of putting in an LS in a 2wd 70. However my 67 with a fairly healthy 408 smallblock and a 700R4 with 3.42 gears knocks off 17 on the hwy.I'm going the LS way just because I got a whole low mileage 2000 truck for $600. It's just cheaper for me. Your mileage will increase but not by a huge amount.If your drivetrian is in good shape now I wouldnt do a LS swap completely based on fuel mileage.But an LS sure runs nice.In my opinion the symplicity of your current setup is worth something too.

[83GMCK2500]

Anyone else? There are a ton of our classic steel trucks rolling around with LS mills...they finish their builds and quit reading this section?

[chuckmc8]

One of the issues, especially with the earlier models (mine is 71 blazer) is that a lot of us are cruising around with LS power, but don't have a working speedometer/odometer. A board member has figured a solution and many are getting started adapting a S10 electric speedo into the 67-72 instrument panel. Stay tuned, MPG info will be coming when the ability to calculate becomes available.

[BR3W CITY]

I get 13-15 local and up to 17+ on the highways locked up around 60. I have a decent amount of drivetrain to turn, so I think the numbers are decent all things considered. Once I'm not running drag radials on the back, my mpg will go up a tad too.

[83GMCK2500]

chuckmc8, I saw that cluster thread and it is fantastic. There is a lot of work that went into it and I think it is great that 67-72 has such a OEM looking solution. 81+ has one from the factory with the 90-91 V-series clusters, they technically fit back to '73 but are cosmetically incorrect.

BR3W CITY, say your build recently, great looking truck. Next to my '83 I spent a lot of time with my dad in his '65 on the farm, such a great truck.

[83GMCK2500]

Bump

[68GMCCustom]

My 4600-4800lb TrailBlazerSS with 4.10 gears gets 12 around town, 14 average, with 16-17mpg being about tops for any highway mpg at 70+.

[bohmankid]

I daily drive my truck. It's a 1985, 3/4 ton, long bed, lifted with 33 inch tires and 4.10 gears. I have a stock 5.3 hooked up to the stock th400. I get 11 mpg.

My milage is bad due mostly to my gears, 3 speed trans, and tires. It's better than the 7 mpg I was getting from the stock 350 though. When I put an overdrive trans in it, that should help a lot.

[Clyde65]

I have a 4.8/4l60e in my 65 and I get an average of 15 city and 19+ hwy. I have gotten 20.5 when there wasnt much wind. these are at 65 and I dont hot rod my truck ( why would i with a 4.8 right?)

If mileage is what your looking for in a big truck like that get a Cumins and a nv4500 with propane injection. your truck is huge and you unfortunately wont see the mileage most of the ls is known for for swaps.

[Custom 68]

I will be able to report back after we start on the power tour. In stock form I did pretty good 18 - 20 but after a cam it dropped now I have a turbo but I am hoping that doesn't hurt during normal highway driving. I have also added a T56 but lowered my rear gear to 4.11:1. Time will tell.
These trucks are heavy and the frontal area is huge, the drip rails don't help matters any. Realistically I would love to pull over 20 mpg and it might be possible but speeds over 70 I am afraid we will run into that wall. I believe I have things dialed in good for this trip but again with my weight I bet I will still suffer.

[Jmiller022]

Im getting right around 20 in mine, its stock and i drive like a granny...lol 65 tops in most cases, and a lot of back roads at 50ish.