Feel good story about the L8T towing heavy

jaquima · January 18, 2022

On 1/16/2022 at 2:53 PM, L8T said:

This will never happen. The Allison is heavy internally and will rob too much hp to make it viable. Not to mention awful fuel economy. Hence why they dropped the 8.1/ally combo years ago.

Love my 2001 8.1L with 4.10 gears. After 21 years, I would not change my purchase for a diesel just because it gets bad gas mileage. Every winter running 87 octane, I get 10-11 mpg mixed driving. Every summer running 87 octane, I get 12 mpg. If I run midgrade gas, I pick up 1 mpg and a more enthusiastic engine response. It has had the common minor repairs but the engine behaves exactly the same way I drove it off of the lot. I have 165,000 and it starts every morning, regardless of the conditions. I tow a 13,000 lb gooseneck horse trailer when fully loaded. The truck handles it nicely as long I keep putting gas into the tank. When I tow it averages about 8-10 depending on the elevation gain of whatever pass I am traveling over. I am not the fastest driver since I want to give my horses a nice ride so the fact that I can't go 80 mph over a large pass is a non factor. I am starting to look at a replacement and wish GM would do another big block. The Allison has been worth every penny. I would look no further if GM paired any gas engine with the Allison.

vucelick · January 18, 2022

On 1/16/2022 at 5:53 PM, L8T said:

This will never happen. The Allison is heavy internally and will rob too much hp to make it viable. Not to mention awful fuel economy. Hence why they dropped the 8.1/ally combo years ago.

I dont believe this was the case. The big block got the same mileage with a 4l80e, 4 speed behind it, which is what the 8.1 suburbans came equiped with. My 01 2500HD has the 8.1/allison combo and now has 180k-ish miles on it and gets 10-12. I believe the motor was rated 345 horsepower. The new 6.6 small block is 410 horse, i cant see it having any problem with the 10/1000 allison

Edited January 18, 2022 by vucelick

L8T · January 22, 2022

On 1/18/2022 at 5:13 AM, vucelick said:

I dont believe this was the case. The big block got the same mileage with a 4l80e, 4 speed behind it, which is what the 8.1 suburbans came equiped with. My 01 2500HD has the 8.1/allison combo and now has 180k-ish miles on it and gets 10-12. I believe the motor was rated 345 horsepower. The new 6.6 small block is 410 horse, i cant see it having any problem with the 10/1000 allison

100% this was the case. 4 speed was awful for mileage due to its gearing not its weight. 10-12mpg (at best) empty was not an acceptable number at that time for majority of customers and still isn’t today. And when the 6.0 came out and got better fuel mileage with more hp/tq it was a no brainer to ditch the combo-and the engine altogether.

There’s always a few guys with lady boners for that combo out there but the fact remains it was an awful combo. The current 6L90E has a lighter converter than any ever used in an Allison, planetary hubs and gears are all lighter, the entire assembly overall is lighter. It works well as did it’s predecessor. No reason for a trans that can easily hold over 1000 ftlbs tq to be paired with a gas engine with much less. Not to mention a totally different tq curve and rpm range.

vucelick · January 22, 2022

12 hours ago, L8T said:

100% this was the case. 4 speed was awful for mileage due to its gearing not its weight. 10-12mpg (at best) empty was not an acceptable number at that time for majority of customers and still isn’t today. And when the 6.0 came out and got better fuel mileage with more hp/tq it was a no brainer to ditch the combo-and the engine altogether.

There’s always a few guys with lady boners for that combo out there but the fact remains it was an awful combo. The current 6L90E has a lighter converter than any ever used in an Allison, planetary hubs and gears are all lighter, the entire assembly overall is lighter. It works well as did it’s predecessor. No reason for a trans that can easily hold over 1000 ftlbs tq to be paired with a gas engine with much less. Not to mention a totally different tq curve and rpm range.

Again, i do not believe that is true. The 6.0 did not get significantly better mileage than the 8.1, nor did it have more torque.

Edited January 22, 2022 by vucelick

kenny_r · January 24, 2022

I agree with that. With the fuel mileage I get with my 6.0, I might as well be at 8.1 liters. Although cruising down the highway at 70 I can squeeze out 15-16 mpgs. City and towing forget about it.