fuel economy question

[kwin]

I am about to go purchase a 1991 2wd Suburban to replace the crew cab short box that I had built and lost in the big fire.
My plan is to lower the sub and convert to 5.3 ls power.
I am doing it for drivability and power but was curious as to what you guys have seen for changes in fuel economy from the factory 305/ 350 to the ls set up.

Thanks for your time.

Keith

[usmcchevy]

14-16 all city driving. Haven't had it on the highway much at all.

[Shon]

my 71 LWB 6.0/4l80e gets 15 no matter how its driven. I have not towed with it yet to see what it will get but that is coming up soon.
If wanitng MPGs then go with the 5.3/4l60e combo.
the 80e is a massive beast to turn and I think thats why they dont get any mileage.

[clinebarger]

85 3/4 ton 2wd............
350/400 I got 10mpg
5.3/4L60E I get 17-19mpg

[awhite4557]

71 SWB 5.3 4L60E 308 gears, 16-17 MPG

[BR3W CITY]

cammed lq4 with built 4l80e, I drove WI to KY and around town for the weekend,
averaged 70mph, drove 2hr 45 min between gas stops avg
70x2.75= 192.5 miles / 11.5 gal avg fillup = 16.7mpg
That was my "overall" # from that trip. I have to go by time because I don't have the fuel settings on my Scanguage setup.

Not bad considering its through the heavy trans, 3:73 rear end and some drag radials..not exactly the most efficient combo. ARound town it was closer to 12-13 but not much below. For a "fun" vehicle its actually one of the most effecient and reliable things I've ever owned.

[Shon]

what cam you have?
clicked your link, Tsunami, or did you change it?
I am going with a SMALL cam to keep the stock TC so as to tow without issues, maybe the extra TQ down low will allow it to pick up a few MPGs.

Originally Posted by BR3W CITY

cammed lq4 with built 4l80e, I drove WI to KY and around town for the weekend,
averaged 70mph, drove 2hr 45 min between gas stops avg
70x2.75= 192.5 miles / 11.5 gal avg fillup = 16.7mpg
That was my "overall" # from that trip. I have to go by time because I don't have the fuel settings on my Scanguage setup.

Not bad considering its through the heavy trans, 3:73 rear end and some drag radials..not exactly the most efficient combo. ARound town it was closer to 12-13 but not much below. For a "fun" vehicle its actually one of the most effecient and reliable things I've ever owned.

[mooseknuckles]

...some say that a aftermarket converter in the 4l80 will help gas mileage?...idk.

[ls1nova71]

Originally Posted by awhite4557

71 SWB 5.3 4L60E 308 gears, 16-17 MPG

Just for reference, I have the same exact truck, '71 swb 3.08 gears but only with the original 350/350 combo and I get 12. Don't remember what my 6.0 swap got, but I'm hoping for high teens with my 5.3.
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[kwin]

Thanks guys thats awesome, looks like another good reason to move forward.

Keith

[TR65]

kwin,

My 1965 C10 with 6.0 litre LS2 / T56 stock from a 2005 SSR (with Cats) gets an honest 17 mpg average over the last year (8000 mi). (I have all the records and have calibrated the odometer) That is a mix of highway and urban, but mostly highway.

Just for reference, my 2008 Vette LS3 with the exact same final drive ratio and 6-speed manual gets an honest 21 mpg over the same roads. All I can figure is Aerodynamic difference.

TR

[mooseknuckles]

...and prob rolling resistance...lol.

[BR3W CITY]

Originally Posted by Shon

what cam you have?
clicked your link, Tsunami, or did you change it?
I am going with a SMALL cam to keep the stock TC so as to tow without issues, maybe the extra TQ down low will allow it to pick up a few MPGs.

Shon, I still have the Tsunami. I prob could have done 1-2 mpg better, but
We didn't re adjust the computer after switchin to the bigger diameter drag radials, and my lockup was being VERY finnicky (only worked about 30% time it should).

I think on top of that, if I had some big tubes instead of the tbss manifolds I'd do a bit better. The lq4 likes the Tsunami and does ok despite the truck intake manifold peaking hp early, if it were an lq9 or I milled the heads a tiny bit it would perk up a chunk. I'm waiting to run FI so not doing that stuff for now.

[homemade87]

I have an 82 w/ 5.3 & 4l60 swb, everything stock. I did have my local tunner do some work on the pcm. Before I was running a tbi w/ 350 & 200r4. At best I got 12.5. After the swap and running a few tanks . I could tell a lot of diffrence before I even calculated it. I used to get right at 200 miles on a 16gal tank. Now I get about 285 miles on a tank. Now I am close to 18mpg. I have not been at cruise speeds for very long so I dont know what it would do at hwy speed. It may not be much better because of these truck being like a sale in the wind. I am hopeing to get around 20mpg ( wishfull thinking ). But in my case I have about 5.5 more miles for every gal I burn at $3.50 gal ($.086 per mile). That puts me at .47 cents savings for every gal I burn. Keith, you may not see these kind of results because the size and weight of the burb. But I thing you will see some improvement. Good luck with your install. The swap was totaly worth it for me.


Buy the way, I am running a 3.23 gear. With my tire height at 28.3 gives me a 200rpm lower than the stock setup at 60mph.