Suppose we're just talking stictly cruising at a steady rpm on the highway in OD. For a 5.3L, what rpm gives you the best fuel mileage? I'm assuming that at some point lower is not better, but does it have something to do with where the torque peak of the motor is, or some other factors?

 

i believe for the LS motors its from 1400-1900 rpms.. im sure more will chime in.. but i think anything over 55mph and you having to deal with air drag.

 

I have always been told 1800 rpm... mine always stays above that so I cant personally vouch LOL...

 

It seems I get my best mileage between 1800 and 2000 rpm, which for me is 70-75 mph on the highway. I've never tried 65, maybe it's better, but I would feel like I should be 80 (years old that is )

 

On my 03 the best speed that I saw some good MPG was around 60-65mph. That was around 1800-1900RPM. There's was a fellow how saw 24.3MPG but he was going 55MPH all the way..............witch is incredible slow if you're drivng in Houston Freeways. Lord knows how many people will get pissed....haha

 

I got 24mpg (before the S/C) when running at 55mph! I was running on fumes and the nearest gas was quite a ways away. Sure I pissed off a bunch of people-but i made it to the gas station!!

 

1700-1900 is sweet spot for great MPG's. I usually go by the MPH on my truck. When I'm dead locked on 68mph hwy cruising, I'll turn out a nice 21 mpg average. That equates about 1750 rpm's with my 3.73 gears and rolling stock 275/55/20 GDY Eagle LS tires at 30 PSI, tail gate up, full tank of fuel, and A/C on. That's awesome, but if you step out of the groove any or a good head wind hits, expect that to drop a bit.
Oh yeah, mines the LQ9 6.0L.

Jim

 

5.3's getting 24 is hard enough to believe.

21mpg from a 6.0L? GM claims like 16 in 1/2 ton models and I don't believe 21 will happen UNLESS you're resetting the average once you get to highway speeds and only counting that. Taking into consideration the on ramps and traffic after refilling will ruin that average. I should point out, that's every bit as good as most diesels and we all know diesels are more efficient by far.

I just have to believe if these engines got anywhere near 21mpg, GM would be ALL OVER that in advertisement.

EDIT: Tuning can help and I know that. But I'm thinking of stock as opposed to modified. GM won't run it lean, fuel economy be damned. They don't wanna rebuild one on their own dime, ever.

 

Not when you have it tuned to run lean while cruising....

When I was playing around with mine, I got around 22-26 on the hwy running pretty lean. I didn't really like it though because I lost a lot of throttle response cause of it.
On a good day I can get 21 with my setup but I typically see about 18.

 

After Hurricane Katrina i got 24mpg out of my truck, and i didnt belive it myself. i tried again and got 23.9mpg.. but since then ive been gettin anywhere from 18-22mpg,, and this is in town. but it depends on how busy i am.. different places and different routes.
So yes they will amaze you with the fuel mileage,,, BUT YOU HAVE TO LEARN HOW TO DRIVE THEM.. that is the key..
and some mods will help it just a lil bit.

but for the average person you will prob get what the sticker says.
haha, how many of us on here are average??