Gears, mpg, could use some wisdom

[SixSpeedSS]

Sounds like we've got the same truck only mine is a long box. I don't know the specs off hand but I know she's heavy.
Probably doomed to poor mileage I guess. The truck is my daily driver, I have to travel around 100kms round trip about 3 days a week for work. My other job is right handy in the small town I live in. But the fuel bill is just killing me.
It wouldn't be the cost but the time I'd be strapped for. The set of rearends I'm looking at buddy wants less than $200 for everything, but the rear needs new seals (and probably at least axle bearings), plus the time swapping the stuff into mine. I work 7 days a week at 2 jobs plus odd jobs on the side.

I don't know what to do right now. Wouldn't be a fun job by any stretch of the imagination. Especially where mine works as it is.

As for the tire swap, the truck came with an almost new set of 265s so I won't replace them until they are worn out. Which might not be for awhile yet.

I'll do some more research and calculations and be sure to post up what I find.

Thanks a lot for the insight SixSpeedSS, any further advice is always appreciated

Anytime. I forgot to add that my truck weighs 5600lbs empty, so I would imagine your truck weighs even more.

I don't know that 285s will make much of a difference over the 265s. I would bet the 3.73s may hurt your mileage on the bottom end though. At least with the 4.10s the truck doesn't have to work as hard to pull out. Your highway mileage may go up, but around town mileage may go down.

 

[Blue95]

Anytime. I forgot to add that my truck weighs 5600lbs empty, so I would imagine your truck weighs even more.

I don't know that 285s will make much of a difference over the 265s. I would bet the 3.73s may hurt your mileage on the bottom end though. At least with the 4.10s the truck doesn't have to work as hard to pull out. Your highway mileage may go up, but around town mileage may go down.

IT will go down in town, you have to factor in not only the higher gear ratio, but also the added rotational mass of the 285 and the increase in diameter.

 

[LoudnLifted88]

I call shennanigans on this. Average 18mpg?????? I could see maybe on a straight highway trip at 55mph across the middle of the country where it is flat as can be, but not an average between city/highway. These trucks just don't get that kind of mileage.

idk he filled it and went we went from maine to tenn. and averaged 18 according to him

 

[96-1500]

How about a full tune up, muffler, tune? much better, easier, more bang for buck and time

Not to diss what you're suggesting but I have to disagree with bang for the buck. A full tune up ran me upwards of $250 (already done), and exhaust work is pretty expensive too (has a 3" dynomax dual in single out, which works well but is nothing to write home about). I do all my own work on the truck but parts are awful pricey. Can't speak for a tune though, have never gotten one done before.
Can't disagree on time though, I really don't want to frig around with ripping out rearends especially where she's getting cold out quick. Been there, done that lol. I'd really like to get a set of 3.42s like my old truck. Hard to find.
I'll probably end up grabbing the 3.73s but I doubt I'll install them before the winter. Jacking up old trucks in a -30 snowstorm isn't much fun, and I don't have time now.

 

[outalne94z71]

I call shennanigans on this. Average 18mpg?????? I could see maybe on a straight highway trip at 55mph across the middle of the country where it is flat as can be, but not an average between city/highway. These trucks just don't get that kind of mileage.

i believe it, my buddies 98 4x4 1 ton rclb gets 19 highway with 350/4l80e/4:10 and 265's, gets 13 towing his 6k# camper

 

[kamokevin]

Not to diss what you're suggesting but I have to disagree with bang for the buck. A full tune up ran me upwards of $250 (already done), and exhaust work is pretty expensive too (has a 3" dynomax dual in single out, which works well but is nothing to write home about). I do all my own work on the truck but parts are awful pricey. Can't speak for a tune though, have never gotten one done before.
Can't disagree on time though, I really don't want to frig around with ripping out rearends especially where she's getting cold out quick. Been there, done that lol. I'd really like to get a set of 3.42s like my old truck. Hard to find.
I'll probably end up grabbing the 3.73s but I doubt I'll install them before the winter. Jacking up old trucks in a -30 snowstorm isn't much fun, and I don't have time now.

I think you would be quite surprised by how much a proper tune can affect both power and gas mileage. The LS engines are much more tuneable but the vortecs will also benefit greatly from a good tune. Couple that with a more freely flowing exhaust, your CAI, and your recent tune up and you could easily net that extra 3 mpg you're looking for, clean up or change shift points, and increase HP and torque.

I don't think you'll like the loss in power you'll see by switching to 3.73's let alone 3.42's, and don't forget that if you change gears you will have to change the gears in the front diff as well if you want to retain 4WD capabilities. I've never changed gears, but from what I hear changing the fronts is a real pain if you're not experienced at it.

I would consider visiting Black Bear Performance's website or get in contact with Mike: http://www.gmt400.com/forum/showthread.php?8107-CUSTOM-ENGINE-TUNING

 

[outalne94z71]

I don't think you'll like the loss in power you'll see by switching to 3.73's let alone 3.42's, and don't forget that if you change gears you will have to change the gears in the front diff as well if you want to retain 4WD capabilities. I've never changed gears, but from what I hear changing the fronts is a real pain if you're not experienced at it.

3:42 and towing will heat up the trans a whole ton more and the truck would be a complete pooch off the line as the 4l80e has a bad 1st gear to begin with

 

[SixSpeedSS]

i believe it, my buddies 98 4x4 1 ton rclb gets 19 highway with 350/4l80e/4:10 and 265's, gets 13 towing his 6k# camper

I still don't see it. Maybe it's just the mountains around here. Anybody I've known that has one of these trucks gets poor mileage. My last K1500 ECLB with a tired TBI 5.7L got 15mpg hwy and 12-13 around town. It had 3.73s and 265-75/16 tires. My K2500 ECSB with a new 5.7L has 4.10s and 245-75/16s, and weighs 400lbs more.

Again, maybe in the middle of the country running 55mph. I tend to run 65-70 in my truck on the highway. The little Vortec is turning 2500 rpm at 70.

My daily driver company car -- 2010 Equinox 4cyl fwd only averages 20-21 per tank combined (aggressive driving) and has gotten a best of 27 hwy if I baby it.

 

[SubLo]

A lot of good suggestions are being thrown out there. But the bottom line, as you alluded to in the OP, is that this is no Civic. Trying to eek out another 2, 3, 4 mpg, while noble, is a little moot as far as I'm concerned unless this is your DD that you do hundreds of miles on a day. In that case, I revert back to the Civic consideration anyway and real purpose of the truck. If the truck is being driven that much, given today's cost of Dino Juice, I'd seriously hope there's some sort of commercial purpose or income derived from doing so.

There are so many variables to consider it's not funny. That truck, when new, and broken in, maybe topped out at 16mpg highway. Now that it's older and not new, the mileage you're getting is not unexpected IMHO. Tire diameter, tire WIDTH, tire rotational mass, wheel rotational mass, wind drag, bearing drag (if they're still up to spec), alignment, payload, road grade, road finish, gas quality, gas grade, and state of tune (many more factors within), all begin contributing to MPG. But, by far, the biggest factor would be driving style. Just sayin...

Throwing out suggestions like "just throw 285's on it" aren't very helpful I hate to point out. That doesn't mean anything in and of itself. "285" is just a width. You need to consider the width as well as the diameter in relation to the current wheel/tire setup and final drive ratio. Not only that, but the tire type (passenger, LT, AS, AT, MT, etc.) as well as the tread design and tire pressure also play huge roles in mileage.

The expense and time of "upgrading" from 4.10's to 3.73's isn't going to be worthwhile - all else remaining the same. Sorry to say. As pointed out, if your engine is laboring up hills now, it will be struggling much more with that change. Any improvement in MPG from going to taller (numerically lower) axle ratios is NOT linear in nature. That is, most folks don't take into account the Law of Diminishing Returns. That is, there is a "sweet spot" or "sweet spotS" engineers factor into original specs in terms of optimal efficiencies, capabilities, durability, and cost. All of these things are affected to some degree by major changes to the drivetrain. For example, you couldn't go down to a , let's say, 2.05:1 axle ratio - half of 4:10, (theoretically) and expect to get 30mpg. It doesn't work that way.

Personally, I'd consider a purpose-built vehicle for a particular task.

My 2 cents.

 

[DGA1]

Your 2500 has the 4L80E in it which is robs more power and is geared differently than the 4L60E. I'm surprised that your engine struggles, only time mine has is when the truck has been waaay overloaded, as in two yards of gravel/dirt in the back, which is about 4,500-5,000 lbs.

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My '96 K1500, LBEC, 5.7, 4L60E, 9.5" 14-bolt with 3.42 gears, and running 256/75-16 tire, does about 15 in combined driving. The truck weighs in at 5200 with a nearly empty gas tank and no one in it.

Time for a tune up maybe.