Fuel Economy from an engine swap: projections?

[Debonair]

The truck is a 95 S10 Extended cab, weighing in at 3300 pounds.

It has the 4.3L V6 and 5 speed. they were rated at 17 city but i've gotten close to 21 MPG from just changing how i drive.

Eventually i'd like to swap engines for fun, a little more power, and possibly better fuel mileage.

one of the engines i'm looking at is the Gen III/IV 4.8L V8.
they come in the full size silverado. they weigh ~4631 pounds, and they're rated at 15-16 city.

If i swap it into my truck mated to a 6 speed manual transmission, do you guys think i would be able to get 21-22 City? maybe even more?

additional thought: my camaro has the 5.7L V8 (the same engine design) and a automatic 4 speed. weights about 3300-3400 and i get 18.5-19 city consistently. I've gotten 20 before.

[beatr911]

From the numbers you present, yeah it sounds like 21-23 city is in the ballpark. Not a lot of mpg improvement, but apparently the 4.3 wasn't developed for low BSFC.

If you want to do a V8 swap it is probably a good choice. Doesn't the 5.7 have cylinder deactivation and get about the same mpg numbers as the 4.8? Maybe that would give more power with the same or slightly better mileage. Prolly costs more though.

If doing a swap, most of us here would be installing a 3cy diesel or at least the 2.2 four popper. That's probably why you're not getting alot of love on this thread.

[Debonair]

Thanks i was wondering about it, if i can get more power and the same (or a little better) fuel economy, its something i'll jump all over.

no it doesn't, the 5.7 is in the Corvettes and Camaros. In the Malibu and Impala they have the the 5.3L has the DoD (displacement on demand) as well as the newer trucks and SUVs.

haha yeah that could be it. I'm entertaining the idea of the 2.0, 2.2, or 2.4L found in the Cobalts and Solstice/Sky. I would be looking for one that has a turbo on it. For the swap i would be better off getting a donor car, so at the right time if i come across one i may jump on that. Availability or lack thereof is my biggest deterrent.

The 4.8s are cheap to come by, a fairly straight forward swap, and its relative to what i know.

[some_other_dave]

Can you swap the gearing? The Corvettes get stupidly-high MPG on the freeway (for a car with a big V8) because they're just barely off idle at freeway speeds, something like 1400 RPM at 60 MPH. And with the massive torque they have, the low revs don't really hurt much.

-soD

[Debonair]

yeah on the LS1 site i see people with 6 speeds getting 30 consistently on the highway.

my truck has 3.08 in it now, i'm probably going to swap it to 3.42 or 3.73