Fuel millage

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DerekTheGreat

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1989 K1500, short box regular cab. Stock 350 TBI & 5LM60 transmission, 3.73 axle ratio. Forget the tire size but they're stock as well. Base timing set to 1 degree. Stock exhaust, stock cat & don't know if it's 2.5" or 3"

Haven't done a pure highway tank in a long time, yet lately I've been seeing 16.2 - 17.1mpg (mostly 16.3-16.8) running about 30% city/70% highway. I limit the top speed to 70mph and try to keep my foot as still as possible on the throttle. I usually end up flooring it 2-5 times per tank anyway and some times have spurts of 80mph or so. More often I do that, the more likely I am to see lower 16's. Oh, I'm also running the A/C too. When I'd run at 80mph & same mix of city/hwy, I was seeing 15.1-15.6mpg consistently, done without running A/C. In the winter, you can easily knock off 1mpg.

Wife's '92 C1500 regular cab longbox with Leer cap & stock 350 TBI & 5LM60 (Yep, confirmed 5LM..) and 3.08 gears has yet to return accurate MPG numbers. Base timing set to 2 degrees. I targeted 1, yet after tightening up the dizzy it came back at 2 and I was too lazy to adjust again. Just had exhaust redone from manifolds to muffler, including a new Walker cat, all 3". Speedometer is still off by a fair margin and it ends up needing work in which I've gotta run the engine and burn gas..
 

fancyTBI

Some of my trucks run and drive
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1992 c1500 RCLB with roller cam 350, TBI, custom prom from Dave from GearHead EFI, throttle body spacer, no cat, no EGR, 2 3/4” exhaust with super 10, 5-speed, 3.08 gears on stock tires. I average 17. My best has been 19.

Before I swapped in the V8 I had a 4.3 and got around 23. Truck was stock.

Let’s say she has “advanced” weight saving technology thanks to the Mid West!
 

bugdewde

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'95 K2500 Suburban
TBI 454
4L80e
3.73
265/75/16 & Aluminum wheels
120k miles
Lots of hills in East Tennessee......

- Highway :
(AZ, NM, TX, OK, AR) - 12 MPG
(East TN) - 10 MPG
- City (East TN) : 9 MPG


Towing (East TN) a 2100 lb Miata with a 1500/2000 lb 20' steel trailer - 8 mpg
 

L31MaxExpress

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'95 K2500 Suburban
TBI 454
4L80e
3.73
265/75/16 & Aluminum wheels
120k miles
Lots of hills in East Tennessee......

- Highway :
(AZ, NM, TX, OK, AR) - 12 MPG
(East TN) - 10 MPG
- City (East TN) : 9 MPG


Towing (East TN) a 2100 lb Miata with a 1500/2000 lb 20' steel trailer - 8 mpg

Seems like it is time to do some tuning to that 454. My personal best 454 tune had a 93 ECSB 2500 454 truck at 17 mpg highway with a 3.73 rear gear. Was a stock engine with a 454SS style exhaust. Stock manifolds and dual cats. Had an edelbrock carb intake with an early model 454 TBI to Carb adapter. EGR was deleted in the tune. Also had a large cap Davis Unified HEI distributor for a 1990 Corvette on it. The large caps have some benifits when you increase the spark delivery. The larger space between the terminals means less potential to crossfire.
 

bugdewde

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Seems like it is time to do some tuning to that 454. My personal best 454 tune had a 93 ECSB 2500 454 truck at 17 mpg highway with a 3.73 rear gear.

Wow! 17 is huge!!!!.
I just bought it a few months ago. Drove it from Phoenix back home to East TN.
Haven't even pulled the plugs yet. Probably needs all new ignition stuff & maybe some fuel delivery stuff as well.
Keeping TBI until I'm forced to pull intake....
 
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Best mpg I've gotten in gmt400 was 23 average on a tank in the limited. 5.7 2wd 4l60.at the time it had brand new tires, 0411 pcm, efans, complete new ignition system. Was a nice frosty November evening driving through the flat corn filled wastes of the I states.the extra flat terrain, cold dense air and brisk tailwind helped for sure.
 

1989GMCSIERRA

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Back in the day when it was stock I was getting 16/17mpg. 1989 GMC regular cab short bed 350 auto RWD stock 3.08 gear open diff

Currently 4.10 or 4.56 (can’t remember exactly) 33s Auburn locker 14 mpg. (Freeway)

It’s non op now as I’m getting around to refurbishing it but I’m gonna run 275/70/15 maybe 275/60/15 so I doubt it will get better. I’ll probably have to regear
 

SK Productions

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I think I average 14 City, 16 Highway
1995 GMC Sierra 2WD 1500 extended cab, 5.7 Throttlebody, 4L60-E transmission, with a camper shell. Everything is stock on it.
 
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