6.6L gasser MPG with new 10 speed Allison tranmission?

UWSkier · October 30, 2023

1 hour ago, Doodle said:

Another update on mileage. I took my 24 on a 600 mile roadtrip all highway this past week. I was fighting a little wind from time to time (I live in Kansas) but I was traveling between 69-80 depending upon if I was on the interstate or state highways. I noticed once you get above 70 mph mileage really starts to drop. At 80 I was getting about 14-14.5 roughly. At 65-70 closer to 16-17. Think my average tank was about 15 or so on that trip. Kind of disappointed in the mileage at interstate speeds as it’s holding 10th gear fine, but also realize these things sit way in the air and are heavy. On one flat stretch I put it on 60 mph cruise just to see the difference and it was closer to 18-19. Only 7K on it so far. My 23 started to get a little better around 10K so guess we’ll see. Also the first tank of fuel I ran was 89 octane. Just wanted to see if there was a difference. I guess I’d say there was no noticeable difference.

yeah, that exponential resistance factor over 70 MPH is a real pain for us lead-footed individuals.

Doodle · October 31, 2023

11 hours ago, UWSkier said:

yeah, that exponential resistance factor over 70 MPH is a real pain for us lead-footed individuals.

To be fair I don't think my LML would do much better than 17-18 at 80 mph. In my area diesel is approaching $1.50/gal more that gas. So it's still cheaper to drive the 6.6 gas than the diesel right now. Kind of glad I have both. Just let the LML sit unless I need to tow heavy.

rjgvt · October 31, 2023

I know it’s apples to oranges but have found with my 1500 trucks with 5.3/6 speed/AFM/Double cabs/ARE cap gets their best mpg at 55 to 60mph driving like a sane person. Once you start hard acceleration to pass, etc., all bets are off. I drive 2 lane roads in VT 75% unless going out of state.

When my AT4 2500HD gasser arrives, I will drive it like my 1500 for the same trips to check mpg. In town trips will suck but I think that goes for any truck.

Doodle · October 31, 2023

11 hours ago, rjgvt said:

I know it’s apples to oranges but have found with my 1500 trucks with 5.3/6 speed/AFM/Double cabs/ARE cap gets their best mpg at 55 to 60mph driving like a sane person. Once you start hard acceleration to pass, etc., all bets are off. I drive 2 lane roads in VT 75% unless going out of state.

When my AT4 2500HD gasser arrives, I will drive it like my 1500 for the same trips to check mpg. In town trips will suck but I think that goes for any truck.

Yeah there are so many factors when it comes to mileage. Every blacktop road around here is minimum 65 mph. We are flat and wide open in western KS. Nothing like Vermont. If I drove 55 here I'd feel like a snail! I also live at 3500' elevation so that makes a difference too, but the flat geography does help mileage. Where I live there are essentially no hills and what we might call a hill people back east would laugh at. No such thing as "steep grades" here. Ha ha.

rjgvt · November 1, 2023

2 hours ago, Doodle said:

Yeah there are so many factors when it comes to mileage. Every blacktop road around here is minimum 65 mph. We are flat and wide open in western KS. Nothing like Vermont. If I drove 55 here I'd feel like a snail! I also live at 3500' elevation so that makes a difference too, but the flat geography does help mileage. Where I live there are essentially no hills and what we might call a hill people back east would laugh at. No such thing as "steep grades" here. Ha ha.

State speed limit here on 2 lane roads is 50mph unless marked otherwise. Interstate is 55 or 65. I generally drive 5 to 7 over unless in town and use cruise control when conditions allow. I’m retired and not always in a big rush!

UWSkier · November 3, 2023

On 10/31/2023 at 5:27 PM, rjgvt said:

State speed limit here on 2 lane roads is 50mph unless marked otherwise. Interstate is 55 or 65. I generally drive 5 to 7 over unless in town and use cruise control when conditions allow. I’m retired and not always in a big rush!

You should get great mileage. I live in Arizona where 80 mph in a 65 zone is considered "keeping up with the flow of traffic."

Dunn · November 30, 2023

so cal too, 90 is normal but wont get too far before traffic of some sort.....full throttle or zero

EPL · December 1, 2023

I averaged 13.8 with my 2023 gas that is somewhat combined highway and some city.

I also just installed a Borla S-Type Cat Back exhaust and hoping to gain at least a full mile per gallon.

Next step is to put an S&B Cold Air Intake to gain another mile per gallon.

Between the two add on's- if I can end up with 16 miles per gallon I'll be tickled pink.

Best interstate mpg at 65/70 was 19, so not too bad.

I live in PA so it's quite hilly here..

I am surprised by some of the numbers you guys are getting with the 2024's and the 10 speed. I thought the mpg would have been much better?.

I'll keep you all posted on any gain after I put the S&B Cold Air Intake on.

kylant · December 2, 2023

16 hours ago, EPL said:

I averaged 13.8 with my 2023 gas that is somewhat combined highway and some city.

I also just installed a Borla S-Type Cat Back exhaust and hoping to gain at least a full mile per gallon.

Next step is to put an S&B Cold Air Intake to gain another mile per gallon.

Between the two add on's- if I can end up with 16 miles per gallon I'll be tickled pink.

Best interstate mpg at 65/70 was 19, so not too bad.

I live in PA so it's quite hilly here..

I am surprised by some of the numbers you guys are getting with the 2024's and the 10 speed. I thought the mpg would have been much better?.

I'll keep you all posted on any gain after I put the S&B Cold Air Intake on.

sorry man. lofty expectations that are not going to be realized

Jim-GA · December 20, 2023

On 12/1/2023 at 6:12 PM, EPL said:

I averaged 13.8 with my 2023 gas that is somewhat combined highway and some city.

I also just installed a Borla S-Type Cat Back exhaust and hoping to gain at least a full mile per gallon.

Next step is to put an S&B Cold Air Intake to gain another mile per gallon.

Between the two add on's- if I can end up with 16 miles per gallon I'll be tickled pink.

Best interstate mpg at 65/70 was 19, so not too bad.

I live in PA so it's quite hilly here..

I am surprised by some of the numbers you guys are getting with the 2024's and the 10 speed. I thought the mpg would have been much better?.

I'll keep you all posted on any gain after I put the S&B Cold Air Intake on.

I assume these are the MPGs from the onboard computer. Have you run a few tank fulls and calculated the MPG yourself from miles between fill ups and gallons to refill the tank? My truck's computer is consistently 11% high on the reported MPG. When I calculate it myself, the number is quite lower. And it is consistently like this, on every fill up.

I think GM is messing with us, trying to make us think the MPG is much better than it really is.

Jettech1 · December 20, 2023

1 minute ago, Jim-GA said:

I assume these are the MPGs from the onboard computer. Have you run a few tank fulls and calculated the MPG yourself from miles between fill ups and gallons to refill the tank? My truck's computer is consistently 11% high on the reported MPG. When I calculate it myself, the number is quite lower. And it is consistently like this, on every fill up.

I think GM is messing with us, trying to make us think the MPG is much better than it really is.

My 22 is damn near spot on. I checked it and checked it numerous times, the dash reading was either .1 up or down. I don't check it anymore...lol..

Jim-GA · December 20, 2023

1 minute ago, Jettech1 said:

My 22 is damn near spot on. I checked it and checked it numerous times, the dash reading was either .1 up or down. I don't check it anymore...lol..

Cool. And my '22 is way off. But I don't really care. I calculate my own and I know what it is.

Peace.

Jettech1 · December 20, 2023

6 minutes ago, Jim-GA said:

Cool. And my '22 is way off. But I don't really care. I calculate my own and I know what it is.

Peace.

And why that is who knows.... different tire sizes maybe?

Edited December 20, 2023 by Jettech1

Flatus · December 21, 2023

My lie-o-meter is anywhere from .8-1.2 mpg off from hand calculations. I would have to say it is the least accurate I have ever had of any of my vehicles.

Jettech1 · December 22, 2023

2 hours ago, Flatus said:

My lie-o-meter is anywhere from .8-1.2 mpg off from hand calculations. I would have to say it is the least accurate I have ever had of any of my vehicles.

That doesn't sound all that bad compared to what I've seen on other vehicles I've owned.