whats the LS swap mpg gains?

[The Big Green]

I have cash to do a LS swap in my 67. I currently have a stock 78ish 350/400t with 882 heads and a RV cam, with a 4.11 gear and 32in tire on rear. I want to be able to take off anywhere with little risk of breaking down and get like 20mpg. What are the best averages made with, 4.8, 5.3, or a TPI setup? I found a 2002 5.3 with 82,000 miles with all that I need to swap for $1100. I need to weigh my options.
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[crazy longhorn]

With the 4.11 gear, & no OD, I dont think you will pull close to 20mpg. I have a 4.8, in my 02 -1500 (2wd). With a 3.73 gear/4l60E, with .7 OD, she gets aroud 13.4 in town, & around 18 on the hyway. Still dreamin about the 5.3 swap in my longhorn....so I cant really say on that one...crazyL

[The Big Green]

At the moment I may just add a taller gear and she how it does. I do like the 5.3 idea but with all the time and money I may do gears and she how it does and stay carbed.
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[awhite4557]

There's a thread on this subject here http://67-72chevytrucks.com/vboard/s...d.php?t=531757

[crazy longhorn]

I have a good running 5.3, hanging on the stand....to be honest, I was not looking for a "hotrod" this trip. My old 383 gets 9-10 mpg in town, & no doubt has far more tork/power than the stock 5.3 can manage. I run OD on the hyway, but havent really checked mileage(my guess around 15mpg). For 3 -3 .5 mpg, my ? is ....can I really give up the ponies(400 hp carburated 383), vs a stock 5.3 (around 300 hp) & spend all the cash, for the fuel system,computer tune ,ect? If nothing else, I have a spare eng for my 02! I parted a wrecked 2000 GMC....when all was said /done, I had $100 in the engine /harness & all + all the extra parts for my silverado. Just fruit for thought.....how many miles would you need to run, to come even on the fuel, vs the cost? crazyL

[Clyde65]

When I did my swap, my 350 was real tired. So I felt it was worth it anyway. I would have been about $15-1800 Into a rebuild anyway and I wouldn't get 12-14 mpg. So I spent about the same amount ( ok about 2250) to put the 4.8 in mine. I get about 15 in city and probably around or just shy of 20 strictly highway. I have around 300hp which my old 350 might have had 150 and got 8mpg on a good day.it was and is worth it to me hands down.
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[BR3W CITY]

my truck makes a chunk over 400 at the crank, and through a 4l80e/12bolt and massive rear meats, I was getting 16-20mpg depending. not bad imo

[ERASER5]

Glock35ispc did a 5.3l/4L60 swap with 3.4 gears. He said he got 20 MPG. Others have claimed the same. I think he had a shorter tirethan you do. With a 4.10, you will lose a lot of MPG, but gain towing and playing ability.

[tallic68]

I have a 68 lwb 5.3/4l60e 3.73 -245/75/16 and I'm getting 18-20. Better yet it starts immediately every time, very smooth running and accelerating. Wish I did it long ago.
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