Truck MPG/towing question.

Can you put a 6 speed auto out of the newer 5.3 trucks behind the 4.8?

Or drop in the complete 5.3/6spd combo and regear to take advantage of the extra ratios?

jstand wrote: Can you put a 6 speed auto out of the newer 5.3 trucks behind the 4.8? Or drop in the complete 5.3/6spd combo and regear to take advantage of the extra ratios?

I like this idea. It sounds like the issue is that you really need a gear between the current 3rd and 4th for towing when you're not in the hills. This would let you have that without sacrificing mpg when running around un-loaded.

I vote leave it alone and embrace your near-perfect 3rd gear towing rpm, or swap in a 6spd auto and leave everything else alone. I like the tune idea as well which would work with either approach.

Bobzilla wrote: That's a helluva mpg hit. Worst towing to date was 12.5 with the 1800lb trailer with a stock C4 coming up from Northern Arkansas. Best towing was first my Nats averaged 14 round trip with the same trailer and a 2000lb Civic. Ethanol percentages went up for my second year and we averaged 13. Unloaded trailer is 15-16 and current unloaded with 4 large adults(~1100 lbs in people alone) and luggage was 19.7 round trip to Florida... then again our speeds may have been a "little" higher than the 70mph we had been running. I know the wife spent almost 3 hours in the 80-85mph range.

Repeat your mpg comparison with that civic or vette in an enclosed and report back,massive difference to an open trailer.

I have a little 16x7 v-nose enclosed and it tows the same at 60+ mph empty or loaded....areo drag is shocking.

kevlarcorolla wrote:

Bobzilla wrote: That's a helluva mpg hit. Worst towing to date was 12.5 with the 1800lb trailer with a stock C4 coming up from Northern Arkansas. Best towing was first my Nats averaged 14 round trip with the same trailer and a 2000lb Civic. Ethanol percentages went up for my second year and we averaged 13. Unloaded trailer is 15-16 and current unloaded with 4 large adults(~1100 lbs in people alone) and luggage was 19.7 round trip to Florida... then again our speeds may have been a "little" higher than the 70mph we had been running. I know the wife spent almost 3 hours in the 80-85mph range.

Repeat your mpg comparison with that civic or vette in an enclosed and report back,massive difference to an open trailer. I have a little 16x7 v-nose enclosed and it tows the same at 60+ mph empty or loaded....areo drag is shocking.

indeed. towing a flat trailer with an aerodynamic car on it that tucks behind the truck is a much bigger mpg hit than an enclosed trailer that is 8-10 feet tall and shaped like a building block that someone rounded the edges on

I'd recommend the 6.0 and a slight drop in the rear gear (like 3.10's or something between 3.23 and 3.10 if you can get it). If you have a chance to do any power additions/upgrades before installing, go for torque over HP.

I tow a 2-3k pound box trailer for karting all over Texas. I've towed it with a new 2008 V6 Silverado, a 2007 4.8 Tahoe, a 1996 Tahoe 2 door 350 and my current, a 2014 Silverado 5.3l.

The 1996 and 2014 towed like a dream and never "hunted".

The 2008 V6 would get about 18 MPG unloaded (extended cab, bed cap that angled up at the back) and about 10 while towing. Part of it was me not knowing to feed the throttle while towing, but most was the serious lack of torque and it's want to kickdown constantly. If there was a whiff of breeze or incline, it'd drop down. I had to learn to feed the throttle and spent the entire drive watching the tach and concentrating on my right foot. It's mentally tiring after an 8 hour drive.

The 2007 Tahoe towed much better. Gas mileage was a little better towing (11), but it was obvious the torque of the 4.8 made a difference. She would still hunt quite a bit, though. I would still spend the bulk of a drive concentrating on the RPM's and longer trips would wear me out.

The 1996 was a torque monster in comparison. She'd shift up to fourth and stay there unless I had to climb a real hill. I'd get around 11 mpg with it, but didn't have to watch teh tach/right foot nearly as much. Only got rid of it because it had 300k miles and lots of stuff falling apart around the truck. With a full time job and karting every weekend, I just didn't have time to work on it. And, it almost left us stranded (dead batter, busted shift linkage, etc) while traveling, so I didn't trust it. Still wish I had it, though....

The 2014 is comical with how well it tows. I'm in 6th gear most of the time, get about 14 mpg towing and barely notice the trailer is even there. I think I've learned that the biggest factor is torque when towing because it doesn't need to kick down as much to maintain speed. She gets about 19 unloaded.

All of the above are on relatively flat Texas roads and averaging about 70 mph.

Oh, and I totally understand wanting to keep that body style. Although my new one is really nice, I miss the beat up 1996 Tahoe. I wish GM still made them...

-Rob

rob_lewis wrote: I'd recommend the 6.0 and a slight drop in the rear gear (like 3.10's or something between 3.23 and 3.10 if you can get it). If you have a chance to do any power additions/upgrades before installing, go for torque over HP.

in my case it's a F150 4x4 4.6L ... I wish there was a simple, inexpensive power adder that would help this heavy pig when I'm towing my CRX

jstand wrote: Can you put a 6 speed auto out of the newer 5.3 trucks behind the 4.8? Or drop in the complete 5.3/6spd combo and regear to take advantage of the extra ratios?

This has been a thought of mine for a while as well. Obviously it will bolt in but controlling it is my biggest concern.

Another thought: long tube headers? Something like he tri-y to promote torque.

In reply to Knurled:

It's actually "only" 5000 lbs. it's been on a scale a few times getting rid of scrap. But the trailer is 1800. I would LOVE a nice lightweight aluminum trailer and shave a few hundred lbs off.

With the price of gasoline today, is doing any costly modifications cost effective. ?

Completely unrelated data point v. Gearing deep.

Our 03 Montero (3.8 v6, not nearly the power your 4.8 makes) towed ~6000lbs without complaint. It's also pulling about 3000rpms @ 80mph in OD. Gas mileage did not suffer more than 1-2mpg while towing, and it took a pretty good hill for it to drop a gear.

I would focus on torque first (unlikely you'll get enough without forced induction or a swap though), then gearing. Gearing is the easy way to make torque. Doing it with motor is the "fun way" and gives a better day to day vehicle.

If it were my truck i'd be putting something in the 3.7-3.9 range then get a tune.

Bobzilla wrote: In reply to Knurled: It's actually "only" 5000 lbs. it's been on a scale a few times getting rid of scrap.

Then the CNG tank in the back of the Sierra must weigh more than I thought, as the shop truck (again, extended cab 4.8 K1500 Sierra) weighs 5800lb by the recycler's scale.

iceracer wrote: With the price of gasoline today, is doing any costly modifications cost effective. ?

Even if fuel was $5/gallon again, it doesn't pay until you get into many, many thousands of miles per year, or if you make an upgrade to coincide with regular maintenance and repair (need a trans anyway, go to 4L80, need rearend rebuilt anyway, change ratios).

Say you go from 10mpg to 12.5mpg, the reciprocal of that is 10gal/100mi to 8gal/100mi. So you save 2 gallons every 100mi. If fuel was $5/gallon, you save 10 bucks every hundred miles. If you spend $2000 on upgrades (a low figure for a DIY engine and rearend swap done by someone who has the long term in mind) you have to drive 20,000mi to break even. That's 20,000 towing miles, since that is the scope of this discussion - daily-driver miles may be better or worse and can make that figure better or worse. Usually worse.

If you get a Good Deal on parts and DIY. If fuel is $5/gallon. If the economy benefits bear fruit.

Until you get to extreme modifications (like converting to CNG, which has GREAT cost-benefit figures for fleets) you're not doing it to save money, you're doing it to feel better either by better economy or reduced RPM (which does not always mean better economy, and in some cases means worse economy). And in the end, your goal is making the driver happy, so do what you want, but be realistic about the benefits.

iceracer wrote: With the price of gasoline today, is doing any costly modifications cost effective. ?

that's assuming that the cost of gas will stay this low ?

Knurled wrote:

Bobzilla wrote: In reply to Knurled: It's actually "only" 5000 lbs. it's been on a scale a few times getting rid of scrap.

Then the CNG tank in the back of the Sierra must weigh more than I thought, as the shop truck (again, extended cab 4.8 K1500 Sierra) weighs 5800lb by the recycler's scale.

Also, K=4x4. You have an extra diff, axles, driveshaft, transfer case etc. Even the front control arms are beefier than the 2wd versions in this chassis.

iceracer wrote: With the price of gasoline today, is doing any costly modifications cost effective. ?

For something that you're going to own for another 10+ years? Why wouldn't it? Especiallyif it makes it a better vehicle for your intended purpose. Like I already mentioned, when we bought the truck, it was spec's exactly as we needed it. Our needs have changed and since GM trucks are grown-up's legos, I can change it to better suit our new needs.

Don't get me wrong, there's nothing WRONG with it, but it could be better.

Bobzilla wrote:

Knurled wrote:

Bobzilla wrote: In reply to Knurled: It's actually "only" 5000 lbs. it's been on a scale a few times getting rid of scrap.

Then the CNG tank in the back of the Sierra must weigh more than I thought, as the shop truck (again, extended cab 4.8 K1500 Sierra) weighs 5800lb by the recycler's scale.

Also, K=4x4. You have an extra diff, axles, driveshaft, transfer case etc. Even the front control arms are beefier than the 2wd versions in this chassis.

Welltheresyourproblem.jpg

I guess I forget that 2wd trucks exist. I only ever see them come from out of area.

Bobzilla wrote: Don't get me wrong, there's nothing WRONG with it, but it could be better.

That is the GRM mindset in your thoughts. We didn't put it there, it is what brought you here.

The problem is that the Hive will have 15 different ways of doing it I keep bringing up the possibility of a Magnusson supercharger but keep getting shot down. They really are very easy to install, they're an intake manifold with a pulley. Tune would be a snap since we already have the truck licensed to HPT for some transmission shiftpoint juggling and speedometer correction after changing the tire size.

Somehow I keep getting shot down To be fair, if it were mine, I'd leave it alone too, since stock tends to be the most wrench-free method of transportation.

Technically it's 1wd lol. Damn open diff.

Everybody has missed the most obvious, best choice.

On mine I went with a taller tire and just towed in 3rd. For my 4wd Silverado that meant cheaper 235/85-16s when I had to buy tires anyway.

In that truck, with 3.4-ish gears, mileage was always better towing a heavy trailer in 3rd, and always better than the 6.0l 2500 that replaced it.

I never thought I would hear anyone discuss the 6.0L and fuel economy in the same sentence!

I had a 2001 6.0L. It was a great towing animal, but a total pig on fuel. I got 9-10 mpg empty. Wind at my back downhill, I might have occasionally touched 12 mpg. I don't think so.

I loved that truck, but it was horrible to feed (fuel was near $5 per gallon). I can't imagine it would ever be able to get near 20 mpg, regardless of the gearing. I ended up selling mine cheap and buying a 7.3L. Now I get 22 mpg.

SVreX wrote: I never thought I would hear anyone discuss the 6.0L and fuel economy in the same sentence! I had a 2001 6.0L. It was a great towing animal, but a total pig on fuel. I got 9-10 mpg empty. Wind at my back downhill, I might have occasionally touched 12 mpg. I don't think so. I loved that truck, but it was horrible to feed (fuel was near $5 per gallon). I can't imagine it would ever be able to get near 20 mpg, regardless of the gearing. I ended up selling mine cheap and buying a 7.3L. Now I get 22 mpg.

There's a lot of things going on with this post. Yes, the 2500+ HD trucks with the 6.0 were gas hogs. They used the 4L80 trans, STARTED in the 3.73 rear end range and had the 14-bolt rear ends etc. Not to mention the chassis itself was heavier so more weight to haul around. Throw that same engine in a divetrain with half the parasitic loss, hauling 1500lbs less to start with and I can only imagine it's going to be better.

Knurled wrote: A 4.8 in a 6000lb truck towing a trailer at sub-2000rpm is going to kick down on the slightest grade *anyway*, may as well shift for yourself instead of having the trans do it under load.

No... just no.

Bobzilla wrote: This has been a thought of mine for a while as well. Obviously it will bolt in but controlling it is my biggest concern. Another thought: long tube headers? Something like he tri-y to promote torque.

A 6 speed swap would easily come to over $3k+. Its not worth it. The factory headers are fine. The $600 to $1k plus the required work buys a lot of fuel.

As for your "6.0L will get better gas mileage", please, just no. It won't. Source? Towing all over hell's creation with a 2008 6.0L 1/2 ton. It got worse mpg than my 1993 K1500. I also towed all over with a 2008 GMC 2500hd w/ 6 speed and 4.10's. It got slightly better mpg than the 1/2 ton if driven properly. 6.0L's are awful for mpg, period.

I'm trying to limit my GRM posts, but this is a thread I can help with. I've been there, done that. Get the tune. Nothing else will make any difference worth noting besides the rear gear change (I wouldn't go higher than 3.73 though or you will kill your mpg). If you don't have electric fans, swap to those, it makes a big change surprisingly enough. Run underdrive pulleys.

Towing in 3rd gear will get E36 M3 mpg. If you could theoretically keep the truck locked in 4th OD with your foot to the floor, it would get better mpg than spinning away at 2500rpm, end of discussion. Anyways, I'm out

HiTempguy wrote: Towing in 3rd gear will get E36 M3 mpg. If you could theoretically keep the truck locked in 4th OD with your foot to the floor, it would get better mpg than spinning away at 2500rpm, end of discussion. Anyways, I'm out

Not necessarily. If you can keep it loaded up in OD but not spend much time loaded enough to get into power enrichment near WOT, then yes, it'll get better mileage. But depending on the tune and gearing spread between 3rd and 4th, it's not uncommon to go from loaded heavily and running in constant power enrichment in 4th to running moderately loaded but leaner in 3rd and see very similar mpg in the end. Basically, a more aerodynamic trailer will often do better cruising in 4th and dropping to 3rd to get the weight up the hills, while a more draggy trailer will often present enough load that 4th gear isn't gaining any MPG (and running the motor near WOT and in constant power enrichment at lower rpm is harder on it than just dropping a gear).

Heck, when I towed a parts Jeep home, I was pushing right up to the 11k GCWR in the Jeep and managed ~11.5 mpg doing 55 - 60 in 3rd (through the hills of the southern tier of NY) spinning around 2300 - 2600 rpm (with a bigger displacement, older technology motor than the 4.8 LS). It would hold speed fine in 4th on flat ground (had to be in 3rd on the hills), but it was almost constantly in power enrichment to do it and showed a 1 mpg gain at best according to the onboard computer.