Guy's with 5.3 in k5 post your fuel mileage up

[brans87]

I am curious what you guy's are getting for fuel mileage with your 5.3 swaps compared to a 350 tbi setup. I wanna do it in my 87 K5 but $ is tight right now but still sparks my interest as my truck likes gas it seems! If it's gonna happen gonna have to find cheap setup as mounts etc go won't skip on high mileage motor though! Thanks in advance guys and gals!

 

[dman1982]

I am curious what you guy's are getting for fuel mileage with your 5.3 swaps compared to a 350 tbi setup. I wanna do it in my 87 K5 but $ is tight right now but still sparks my interest as my truck likes gas it seems! If it's gonna happen gonna have to find cheap setup as mounts etc go won't skip on high mileage motor though! Thanks in advance guys and gals!

I'm going to be doing this swap into my 84 k10 here real soon...ive heard of some guys getting up towards 25-26 highway....where ya at in nc?

 

[paratrooper307]

I'm going to be doing this swap into my 84 k10 here real soon...ive heard of some guys getting up towards 25-26 highway....where ya at in nc?

I'd be interested to see too. 25-26 mpg highway seems VERY optimistic for a gasser square body unless it's going downhill. Even the 6.2 diesels would struggle to get that kind of mileage. I'd be surprised if you get 18 in a K-Series. I think the newer 5.3 4x4 Silverados are only rated at 21 tops, and that's with a more efficient aero design and a 6 speed auto.

 

[dman1982]

I'd be interested to see too. 25-26 mpg highway seems VERY optimistic for a gasser square body unless it's going downhill. Even the 6.2 diesels would struggle to get that kind of mileage. I'd be surprised if you get 18 in a K-Series. I think the newer 5.3 4x4 Silverados are only rated at 21 tops, and that's with a more efficient aero design and a 6 speed auto.

i think its possible with the right gears, ill let you know, i normally mess with the k10 trucks, pretty new to this site, and seems like there is a lot of knowledge on this forum..i normally am on the 67-72 truck forum... I'm going to be doing the swap here in the next few weeks, right now i get about 15 city with my stock k10, and about 8 highway lol....but as far as fuel mileage goes if i can just average 20 mpg's ill be happy

 

[80' 427]

I have a hard time believing it would get 25-26 off a cliff with the wind. Of course if you are driving everywhere at 45 mph, with a egg under the pedal, with the wind, down hill, and a sail, maybe.

 

[dman1982]

I have a hard time believing it would get 25-26 off a cliff with the wind. Of course if you are driving everywhere at 45 mph, with a egg under the pedal, with the wind, down hill, and a sail, maybe.

haha...i understand what yours saying....im just going off of what I've read, i can't base it off of my experience yet....yet haha...i do see it a lot more possible in the c10's than the k10's...but the main reason I'm doing the swap is for the power, performance, and drivability as i like to drive my truck on a daily basis...i got my 00 trans am I drive daily as well which is capable of getting good mileage but i crush that egg every time i take off

 

[80' 427]

I have been tossing around the idea of a ls swap into my k10, or a qjeted 454. It gets about 6 now, I figure more tq and the same mpg would be OK.

 

[dman1982]

I have been tossing around the idea of a ls swap into my k10, or a qjeted 454. It gets about 6 now, I figure more tq and the same mpg would be OK.

if i had a big block i might think of a efi live or another one of those kits...but the ls swaps are about as much or maybe even a little cheaper than one of those kits

 

[80' 427]

believe it or not but a properly tuned Qjet will pull numbers very close to a FI system. For a truck that my wife claims as hers that will never see angle I think fi would we a waste of time.

 

[dman1982]

ya man....id have to agree...ive heard that about the qjets...i had one on a olds i had a while back...worked pretty good...ive mostly had edelbrock's had pretty good luck with them

 

[Greg Ducato]

I have a 2013 Tahoe Z-71, 5.3 V-8, 6 speed automatic, 3.42 gears, 31 inch tires, one inch front leveling kit. Average mpg is about 14, extended trips at 70mph or more, 16.5 mpg. These are real world numbers on todays fuel blends with a vehicle far more aerodynamic than a Square body GM that has been lifted. Take it for what it is worth but if anyone tells you they are getting better mpg than this I would have to question their math skills.

 

[dman1982]

I have a 2013 Tahoe Z-71, 5.3 V-8, 6 speed automatic, 3.42 gears, 31 inch tires, one inch front leveling kit. Average mpg is about 14, extended trips at 70mph or more, 16.5 mpg. These are real world numbers on todays fuel blends with a vehicle far more aerodynamic than a Square body GM that has been lifted. Take it for what it is worth but if anyone tells you they are getting better mpg than this I would have to question their math skills.

like i said, just going off what I've heard....either way tho...it will be a improvement on my k10 when i do the swap...but when i do the swap ill be sure to report my numbers on fuel economy...im sure ill be getting better than 15 around town and 8 highway (I'm swapping my gears as well)...and i can do the math for fuel economy lol

 

[number_juan]

I get about 550 miles on a full tank of gas (31gal) before it gets scary, roughly high 17s. 5.3/700r4/np208, 32 bfg all-terrain, 3.42 gears, stock height, still tuning.

 

[big dan]

My k10 with 3.73s and sm465 with 33x12.50s and a 4.8 averages about 15-16 for my normal commute to work which has lots of hills. On the freeway I have gotten up to 18mpg on a 60 mile trip running 65-70 mph with no overdrive. I know that some may not believe that but I checked using gps and filling my tank before and after the trip. I imagine with overdrive I could see 18-20.

25+ though I find real hard to believe. Maybe a 2wd with perfect gearing and the right winds might see 25 but that's pushing it.

Despite fuel mileage though it is by far the best thing I have ever done to my truck. I plan on having another one real soon with better gearing for highway driving. drivability improved greatly with the swap. Cold weather starts are no problem. The only thing I don't like about it is that its easier to steal now that its easier to drive.

 

[Blue85]

MPG numbers are somewhere between fish stories and political speeches.

That being said, here's some numbers...
My 2005 gets 16MPG driving around in 4WD on snowy roads, 13MPG pulling a trailer and over 20MPG on long highway trips. That's about 5400 lbs, which is similar to a K5, but more aerodynamic. So I bet 18MPG is possible with for a 5.3L K5.

EDIT: I bought this particular configuration Yukon XL for MPG - it's the family station wagon. It is 5.3L, 3.42 gears and 4-mode transfer case (2H, 4-Auto, 4-H, 4-L). The 6.0L with 3.73 gears is more fun to drive, though! The full-time AWD/6.0L/3.73 Denali package seems the worst - the ones I drove would do 13MPG highway and no low range (yuck).

 

[shady]

my 05 couldn't get 20 if I had a tail wind guess their all different. on one trip at 55-60 I managed to get 15. that's it. didn't impress me much. the reason I bought it was because of my buddies 07 getting 19-20. I expect my burb to get about 16-17 after the 5.3 swap. it gets 14-15 now with the stock 5.7/700r4/208/3.73 combo and 33's

 

[Rugger187]

I have an 89 K5. It has a 4" lift, Dana 60 front, 14BFF, 3.73 gears, 35's, 700R4, and a 383 Stroker TBI. I built it with a mild cam. I get 19-21 on the freeway going 65. Around town I don't dare try to record the mileage....

 

[y5mgisi]

My 90 burb with the 5.3 had been getting 12 with strictly in town driving. I can't imagine getting any better than 15 on the highway.

My 12 gmc with the 5.3 with DOD and VVT gets 14.8mpg overall running average over 16k miles. Lots of it is in town. On the highway at less than 60mph it will get 22 mpg tops. Running over 70mph drops it down to 18.5mpg.

 

[handloader90]

My k10 with 3.73s and sm465 with 33x12.50s and a 4.8 averages about 15-16 for my normal commute to work which has lots of hills. On the freeway I have gotten up to 18mpg on a 60 mile trip running 65-70 mph with no overdrive. I know that some may not believe that but I checked using gps and filling my tank before and after the trip. I imagine with overdrive I could see 18-20.

25+ though I find real hard to believe. Maybe a 2wd with perfect gearing and the right winds might see 25 but that's pushing it.

Despite fuel mileage though it is by far the best thing I have ever done to my truck. I plan on having another one real soon with better gearing for highway driving. drivability improved greatly with the swap. Cold weather starts are no problem. The only thing I don't like about it is that its easier to steal now that its easier to drive.

@big dan I tried to PM you, says your inbox is full.

I'd like to pick your brain on the 4.8l LS bolting up to a SM465... what parts you used etc.

 

[Larry]

Smaller engines do not always equal better fuel ecomomy. The Polar Bear 1989 V2500 Suburban w/ 8.1L pulled a total trip average of 13.9 last month on our annual Desert Trip. The best I ever got out of the old TBI 5.7L was 11. The trip was around 1,850 miles with a mix of highway, mountain passes and about 600 miles of off-roading. Not too bad of mileage for a big tank with damn near 500 cubes under the hood. Our old 2004 Tahoe Z71 w/LM7 5.3L used to get around 13 city and 17 highway and had a lot less power but I doubt that mileage would be expected in a swap into a square body. Don't overlook big engines. A lot of it has to do with driver habits and the trans. Big engines don't have to work as hard to propel heavy metal down the road