What kind of mpg should I expect after a engine swap?

[Plunkett]

Ok, so to start off. My truck is an86 chevy silverado with a 305/700r4 transmssion, 6" lift, 35" tires,and 4.56 gears. I don't ever expect this thing to get amazing fuel mileage. I'm currently looking at twodifferent engine swaps. One being swapping in a gen3 5.3 motor and bolting it up to my 700r4 transmission, the other idea was doing a 350 with a street avenger carb, comp cams 268 cam, and lt headers. I don't drive this truck hard. What kind of fuel mileage can I expect to get from both swaps?

[N2TRUX]

What are you getting now?

[Plunkett]

Originally Posted by N2TRUX

What are you getting now?

The speedometer is off due to the gear change and larger tires.I was getting between 10 and 11 before the lift and I'd say it's around the same b/c I drive the same amount each week and use the same amount of gas.

Glock, the truck is a 4wd.

[RaysK20]

Cant comment on the over drive, but my 73 k20 gets 13 highway with a well worn 350 edelbrock performer intake and carb, stock manifolds and dual exhaust. I am running 235-85-16 tires threw a th350 and 4:56 gears. While the truck is not lifted, I just swapped off the wide 33-12.50 tires to the 235 and my mileage went from 11 highway to 13. I am currently planning on a 350 rebuild similar to above but raising the compression, a comp 260 cam and headers. I expect to be up around 14-15 mpg with a fresh setup.

[C-10 simplex]

The 2005 silverado 4x4 with the 5.3 i rented got just about 20mpg and this was with "normal' tires. So, i would guess under 20 for your app.

[glock35ipsc]

I can only speak for the 5.3, but considering my setup is:

4L60E trans (2wd), 3.42 gear, 28" diameter, .70 O/D ratio, at 75 mph = 2155 rpm

Yours should be:

700R4 (same gear ratios as the 4L60E), 4.56 gear, 35" diameter, .70 O/D, at 75 mph = 2298 rpm

I get 20-21 mpg on the highway. You should expect a little less than that due to the height of teh truck, tire diameter, friction loss from the transfer case, etc. At least I am assuming with a 6" lift and 35's that it's a 4wd.