Ls conversion

[F-ingrob]

Im thinking of doing a LS conversion
In my 87 K5
I already got rid if the throttle body and stock motor due to lack of power and towing capability
The new motor has plenty of pkwer but now i want fuel economy
What are some milages you guys are seeing
With an LS
Thinking of a LS 5.3
I have 35" tires and 4.56 gears with a 700R4
Thanks

 

[TreeFarm]

My 5.3lm7 with ls6cam, sm465, 4.56s, and 37”s would get 13mpg doing 80 on the highway.

Overdrive and slowing down would help a bit I’m sure

 

[dyeager535]

There are so many factors to economy that what one person gets, another will not. As mentioned, speed will probably make the most difference.

No LS experience, but I'm willing to bet it would be nearly the same as what I have seen over the years.

1983 K5, 305/q-jet/700r4/3.08/31" tires/10 bolt. Best ever MPG on a tank: 17.
~1985 K5, "gen1" 350/q-jet/SM465/3.42/33" tires/10 bolt. Best ever MPG on a tank: 17.
~1985 K5, "gen1" 350 w/roller cam/TPI/Vortec heads/SM465/3.42/33" tires/10 bolt. Best ever MPG on a tank: 17
~1985 K5, Vortec 350/TPI/SM465/3.42/33" tires/14SF. Best ever MPG on a tank: 18

My best economy has always come on flat ground, around 50MPH, in cool weather. Not a big surprise.

Some economy can be gained from overdrive, but really, keeping the speed down is going to be the major improvement. Drag increases fuel consumption exponentially. You see that a bit less in aerodynamic vehicles, these are nothing of that sort. A decrease in displacement and OD will help, but trying to get decent mileage out of these things, without using a 6.2L diesel, is an exercise in futility. The highest gas MPG I've heard of that I feel credible, is 19MPG in a Suburban that was tuned to run lean on the freeway.

 

[Tiger5]

I did a 5.3 with a 4l60e. Used an Advanced adapter to keep my transfer case. I bought a 2002 Suburban as a donor. Lol, it had 260000 miles on it. I had engine rebuilt with a custom cam mild head work and headers. Machine shop in Topeka, Kansas did the engine. Siebert Machine shop, he specializes in LS stuff. Transmission done with a shift kit. Had a basic tune in it until last Thursday until I had it tuned by a real knowledgeable tuner. And what a difference it made. A shop in Peculiar, Mo. did it. Knights Performance. The owner Todd was outstanding. This LS expirence was great and I highly recommend it.

 

[Space Toast]

I did a 5.3 with a 4l60e. Used an Advanced adapter to keep my transfer case. I bought a 2002 Suburban as a donor. Lol, it had 260000 miles on it. I had engine rebuilt with a custom cam mild head work and headers. Machine shop in Topeka, Kansas did the engine. Siebert Machine shop, he specializes in LS stuff. Transmission done with a shift kit. Had a basic tune in it until last Thursday until I had it tuned by a real knowledgeable tuner. And what a difference it made. A shop in Peculiar, Mo. did it. Knights Performance. The owner Todd was outstanding. This LS expirence was great and I highly recommend it.

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Curious about what mounts, headers, radiator, etc you used...been looking at BRP kits

 

[sweetk30]

in my opinion and others online i have started to read stay away from dirty dingo for mounts and brackets . thinking about it still burns me bad . . .

here is a few vendors on this site who offer stuff .

http://offroaddesign.com/catalog/Gen3+GMMotorMountAdapterPlates.htm
http://www.offroaddesign.com/catalog/motormounts.htm
http://www.offroaddesign.com/catalog/enginecrossmember.htm

or

http://diy4x.com/product.php?productid=17694&cat=252&page=1
or no spacer/adapter direct bolt up kit and cheeper . http://diy4x.com/product.php?productid=17865&cat=252&page=1

 

[Tiger5]

I used Hooker mounts. Schoenfeld headers and Griffin radiator. The headers fit good on passenger side but hit transmission linkage on drivers side. I may change those out one day. And the radiator is good.

 

[F-ingrob]

I picked up a 2004 chevy avalanche with a 5.3 so I think im going to go through with the swap
Next question is the harness and computer what type of harness do i need to get or need
Can i just use a stand alone with trans controler and fan relays
I have looked up few but its a little confusing

 

[TreeFarm]

Use the stock harness and computer. It's already there

 

[Tiger5]

Strip the harness out of Avalanche along with the gas pedal and module. They all match. You will need to send the harness to someone who converts them. This means strips out all the unnecessary crap and sets it up for all the stuff you will need. It costs about $300.00 to $600.00 to get it done. I had a local guy do it for $600.00 but prices have come down. A friend of mine used a guy in Minn. He charged $250.00 for a custom set up. Kevin 651-447-3946.

 

[sweetk30]

could do it your self if you dont mind playing with wiring . http://www.lt1swap.com/2000harness.htm

 

[TreeFarm]

Plenty of YouTube videos walking you through how to do it yourself. The stock battery cables and power steering hoses will work in the square

 

[Tiger5]

Ha ha boys. Not me. I paid for that stuff. I want it right and tight.