65impalass

I have an Impala with 4.11s in rear. I am planning a swap in the future and trying to find best choice. It would be mostly country and highway driving (50-75 MPH). 30 plus miles to work or other civilization. I am looking for economy first performance second. With the 4.11s and a six speed it should be fun, no matter what is under the hood.
With a .50 t56 final drive would be 2.05, 3500lbs.
What do you guys think? Thanks in advance.

Earl Filter

iTrader: (1)

Not enough difference to matter for mileage, and the 5.3 will give you better performance and should be easier to find. I would just be sure to get a good tune.

Irish350

iTrader: (14)

im with brandon

speedtigger

iTrader: (16)

A smaller motor will almost always get better mileage when cruising as long as the vehicle is not too heavy which should not be the case with your car. One more consideration is compression ratio. Higher compression ratios get remarkably better fuel economy in part throttle situations.

COSTIGAN86

iTrader: (8)

Go with the 5.3. The mileage difference between the two won't really be noticeable but the power increase will. I've had two identical 2000 Silverado 4x4s. One had the 4.8 with 4.10s and the other has a 5.3 with 3.73s. The 5.3 averages a mile or two better per gallon.

chuckd71

iTrader: (23)

A 5.3 might have enough torque to let you use those upper gears more frequently if you are just cruising.

65impalass

Thanks for your input. After posting this i noticed the 5.3 has a higher cr that, and the possibility of all aluminum points to 5.3.

Isolde

iTrader: (4)

LR4 4.8L and LM7 5.3L both had 9.5:1.
Back in '99 GM themselves said, regarding fuel efficiency, that the 4.8L is "a real sweetheart"
Around here, the 5.3L runs $500, while the 4.8L runs $200.
Note that costigan's reply is irrelevant, it's a 5500# truck, with lots of aero drag, and the gearing also favored the 5.3
Also note that the 5.3 was never offered with a stick, while the 4.8 was, so all you'd have to do is delete VATS, and recal the speedo.
You could put the 4.8 crank, rods and pistons in the 5.3 aluminum block.

thunderstruck507

iTrader: (18)

I would go for the 5.3 all the way

fbrown540

I have a 2008 Express Van with 4.8/4L80E, 295HP. Moves real good for 5300 lbs. Also gets 22mpg at 70mph on long trips. I would think that a 4.8 might get 30 mpg in a 65 impala and would have better performance than any of the stock small blocks of the era. The 2008 engine had improvemnts for gas mileage compared to the 2007 and older.

Isolde

iTrader: (4)

There is some validity in more cubes with less rpm at cruise. But you declared 4.11 gears. As such, the 5.3 isn't necessary. More fun, sure.
There are very few GM performance cars getting 35 mpg, but I've heard of 2 believable ways to get there.
Legend has it that GM got an '05 'vette there by installing a DoD LS2 prototype. That's plausible, but the initial cost is high.
If you're concerned with the cost to keep fuel in the tank, then you must therefore be also concerned with the initial cost of the engine.
In support of the small cubes approach, there are many examples, but none are LSx, and only 1 will run 12s.
The L67 Fieros.
You have more weight and drag, plus your car isn't transverse-engine compatible, but the DoD LS2 isn't the only way to get 3100 pounds to do low 12s and 35 mpg.
Less cubes is a viable way to improve mileage, especially when you have plenty of gearing.

dogger

iTrader: (1)

Mileage difference on a 1/2 truck is about 2 miles to the gallon between 4.8 and 5.3 I've had the 4.8 for use and drove a 5.3 regularly if mileage was a enough of a concern to change out the gears and set the car up for cursing I'd use the 4.8 other wise the lost HP would be worth it. BTW the 2 mpg was only when I was trying for good mileage other wise it sucked fuel down as fast as a 5.3

dueces

iTrader: (2)

What are you predicting the car will weigh in at? I think in the end you will be satisfied either way, but as a personal preference I would say the 4.8L. Your really not missing much hp, but you will be down some torque, which really won't matter when your cruising at 75mph.

Isolde

iTrader: (4)

Dude, it's a 2.05:1 final gear. Same as the heavier, drag-ier Silverado XFE , with MUCH taller tires, uses to get 22 mpg.
By comparison, ALL the '98-'02 T56 Z28s had a 1.71:1 final. The 4.8 wouldn't be happy with that, 1430 rpm at 65 mph,
but the XFE is managing 1470 at 65, and even if this guy uses 27" tires, he's still over 1660 at 65.
My 4.3 work truck ( full size ) has no issues with 1610 at 65.
These evidences all point to the 5.3 being too much for best MPG.

65impalass

Thanks to all you guys, it is refreshing to get well tought out answers when asking about gas millage instead of "get a 4 cyl for daily driving". I would like to get 30 mpg if posible and then I would be able to drive it alot. I wish i didnt have 4.11s, I could save money running my 4l60. I see people saying 4.8s can be had cheep but i have not seen it yet. This project is a long way off so no rush.

speedtigger

iTrader: (16)

I see them for as low as $300 on: http://car-part.com

This is where I found my engine listed.

65impalass

thanks speedtigger, i am just window shopping at the moment. That i a beautiful Buick, When I was shopping for my first car I looked at a 65 GS $400 ran, had some rust but not bad. Those were the days (1980).

speedtigger

iTrader: (16)

Back in the day................ It is amazing what we could have bought back then.