4.56 gears K2XX 4x4 L83

[truckguy82]

20 minutes ago, Grumpy Bear said:

Patients grasshopper, patients. 

 

If his starting point is 12 mpg on a factory DIC which are 8 to 10% happy, he has only one way to go, eh? I was drawn by the comment about the AFM duty cycle. That's what go my attention. 

Yeah but 30% is absurd. There is really nothing to believe short of a precision and repeatable test.

 

any sort of hand calculation you would have to just chalk up to a difference in driving

 

there is no way that all of GM’s engineers would be stupid enough to not realize some 30% gain in efficiency when they are willing to spend millions on a 1% increase.

 

reality is that increasing the axle gears is at best going to net the same mpg, you’re trading higher rpm with increased afm activation.

[aseibel]

9 minutes ago, truckguy82 said:

Yeah but 30% is absurd. There is really nothing to believe short of a precision and repeatable test.

 

any sort of hand calculation you would have to just chalk up to a difference in driving

 

there is no way that all of GM’s engineers would be stupid enough to not realize some 30% gain in efficiency when they are willing to spend millions on a 1% increase.

 

reality is that increasing the axle gears is at best going to net the same mpg, you’re trading higher rpm with increased afm activation.

I don't see where the OP mentions any tire size, but I'm assuming he has large tires. I don't know why else a person would make this drastic a gearing change. So since I'm assuming he had very large tires, that was killing his MPG (12 average). Now with the new shorter gears, the engine speed to ground speed ratio is back closer to what a stock truck has so his MPG is only returning to "normal". So I can see a decent improvement in city MPG. But that will be cancelled out on the freeway when he's running at 3,000 rpm.

[300 Blackout]

I was drawn by the comment about the AFM duty cycle. That's what go my attention. 

I’ll pull the data log off of my tuner to compare the before and after afm data. That will be more objective info of the duty cycle than basing it on gas mileage.

[300 Blackout]

truck - I think the vehicle is being offered with features that cater to a large variety of owners and driving styles. Most of my driving is city, with larger and heavier wheels/tires, so the mpg increase I have observed is relative to the modifications and driving style that I have. A 4.56 gear would not necessarily result in an increase in fuel efficiency for other drivers. For me, so far, it has.

 

aseibel - I have the 20” All Terrain polished aluminum wheels with 275/65/20 Cooper STT Pro tires. The wheel/tire combo weighs 115lbs each. They are 33.5” measured diameter. New, they were closer to 34”.

 

[300 Blackout]

Now with the new shorter gears, the engine speed to ground speed ratio is back closer to what a stock truck has so his MPG is only returning to "normal". So I can see a decent improvement in city MPG. But that will be cancelled out on the freeway when he's running at 3,000 rpm.

Yes, exactly. Most of my driving is around the city so it made sense for me. I am really only returning back to normal.


Sent from my iPhone using Tapatalk

[truckguy82]

1 hour ago, 300 Blackout said:

truck - I think the vehicle is being offered with features that cater to a large variety of owners and driving styles. Most of my driving is city, with larger and heavier wheels/tires, so the mpg increase I have observed is relative to the modifications and driving style that I have. A 4.56 gear would not necessarily result in an increase in fuel efficiency for other drivers. For me, so far, it has.

 

aseibel - I have the 20” All Terrain polished aluminum wheels with 275/65/20 Cooper STT Pro tires. The wheel/tire combo weighs 115lbs each. They are 33.5” measured diameter. New, they were closer to 34”.

 

Same wheels i have, I average 10mpg in the city

[KARNUT]

Back in the 70s- 80s our family car usually was an impala. I had 13 total. Usually small blocks running 273 gears. I would as a rule change the gear to a 373 posi. The cars usually stayed in town and she would usually get an increase in mileage to 2-4 MPG. It was during the double nickel days my Hwy mileage would drop by 2 MPH. It didn’t take her long to figure out the real reason why I would do that, I had a lead foot. It didn’t take her long to get one too, the gear change would make a big difference in acceleration.


Sent from my iPhone using Tapatalk

[300 Blackout]

What is your highway RPM now at 70mph? or even 80 for that matter.

 Engine RPM is 2175 at 70mph according to the data log on the tuner. It stayed in V4 most of the drive and averaged 22mpg on the computer using 87 gasoline.   IMG_6244.HEIC

[300 Blackout]

Same wheels i have, I average 10mpg in the city

Sounds to me like you need some new gears :-)

[SkiDooNick700]

39 minutes ago, 300 Blackout said:

 Engine RPM is 2175 at 70mph according to the data log on the tuner. It stayed in V4 most of the drive and averaged 22mpg on the computer using 87 gasoline.   IMG_6244.HEIC

Not bad, I guess if you were goin 80 it'd start gettin up there a bit, like 2400 - 2500 rpm, idk?

 

I noticed in my 6.2 NHT when I drive in Tow Haul, the V4 stays on longer.  maybe on my way home today from work I'll drive home in Tow Haul just for kicks to see how much extra V4 time I get lol. Somewhat similar concept as your short 4.56 gear, tow haul keeps the RPMs up a bit since it doesn't shift so soon.

[Grumpy Bear]

7 hours ago, truckguy82 said:

Yeah but 30% is absurd. There is really nothing to believe short of a precision and repeatable test.

 

any sort of hand calculation you would have to just chalk up to a difference in driving

 

there is no way that all of GM’s engineers would be stupid enough to not realize some 30% gain in efficiency when they are willing to spend millions on a 1% increase.

 

reality is that increasing the axle gears is at best going to net the same mpg, you’re trading higher rpm with increased afm activation.

Garbage in, garbage out. Hand calculation as an individual point is as useless as the DIC. This is were statistics is helpful. Specifically long term averaging. 

 

I wouldn't hold that thought very tight. GM once made 350 motors that got 12 mpg in a half ton. They've doubled that since the 60's and we know that outfits like Mercedes Benz have technologies that produce 50% thermal efficiency. GM is about 15% behind them but double their previous best. I can't explain it and it does seem irrational. 1989 Honda HX had an EPA sticker of 44 and they have gone backwards now for decades. Their new IMPROVED Insight gets worse mileage than the original. 

 

I have shortened gearing and reaped an increase in fuel efficiency. It isn't common but it is possible. I think his case will be one considering his starting point isn't OEM conditions. 115# wheel weight! OUCH. 

I'm not tossing the baby out with the bathwater. I'll just watch it play out and see what gems I can pick out it. 

[BlueTopaz14]

Sounds to me like you need some new gears :-)

Did you keep your G80 in? Or do you even have one?


Sent from my iPhone using Tapatalk

[MN1(SW)]

This is very intriguing.  When I get back to the states, I plan on putting a sleek camper shell on the back as well as installing either a Zone or BDS 6" lift.  I'll most likely put a bunch of gear in the bed for overland/survival stuff.  Since it'll be adding a lot of weight, I might drop my 3.42s down to 4.10s.  I'd also like to install a manual locker in the rear and maybe an LSD in the front.

[300 Blackout]

Did you keep your G80 in? Or do you even have one?

Yes, I have and kept the G80 locking rear differential. I haven’t experienced any problems with the G80 (yet?) so it isn’t that high on my list of upgrades.

[BlueTopaz14]

Yes, I have and kept the G80 locking rear differential. I haven’t experienced any problems with the G80 (yet?) so it isn’t that high on my list of upgrades.

Phew, glad I’m not the only one then lol. I’m the same way about it, seems like they really only have problems when they are severely mistreated. But as for being used what they are designed for I have yet to have one fail me.


Sent from my iPhone using Tapatalk