6.0l vortec vs 8.1l with allison gas mileage

[TerryandKim]

I'm considering the purchase of two different trucks.
Has anyone had experience with comparing the gas mileage for a a 6.0l vortec vs an 8.1l paired with the allison transmission??
For my purposes the 6.0 is in a 2009 1500 4WD Ext Cab and the 8.1 is in a 2001 2500 4WD Ext Cab. I will be using the truck for towing a 7000 lb trailer in the summer and for a light duty work truck the rest of the year. Thanks!

[mbrower]

I have the 8.1 3500 dually and have been very happy with it. Bought it brand new in 2001 and have had minimal problems with it. Mostly electrical switches and body hardware. I have towed trailers ranging in weight from 7,500 to my current fifth wheel of 16k lbs. With 7k pounds behind it you will barely know its back there. I got between 9 and 9.5 mpg towing depending on terrain but never less than 9. I average around 8 mpg towing my current fifth wheel. Empty, I always get around 10-11 mpg but mostly 10 with mixed driving. Range when towing is about 225 miles before refueling but I'm usually ready for a leg stretch by then.

I cant comment about 6.0 cause I've never own one but I had heard they tow fine but at higher RPM.

My final thoughts are if I had a choice (and I did) I would go with the 8.1 for two reasons. If you ever upgrade to a heavier camper (which I did)you will probably kick yourself for not opting for the towing power of the 8.1. Second and most important is the Allison transmission. These transmissions are just about bullet proof and when towing its one less thing you have to worry about.

[Need-A-Vacation]

If I remember correctly, the 6.2 didn't come out until '09 for the Denali, and '10 for the Silverado.

Understand the '09 wih the 6spd trans is a different animal compared to a 4spd 6.0 truck.

[ksu_j]

I've got an 8.1 3/4 ton Suburban right now and pull a trailer that is 6700lbs GVWR. It's probably around 5500-6000 when loaded although I've never weighed it. My 8.1 pulls that thing like it isn't even back there. It's a 4speed with 4.10 gears. I can set the cruise at 65 and sit back and relax and it'll just pull and pull without hardly ever even downshifting. I love it for pulling. Unfortunately, it is TERRIBLE on gas the other 90% of the time I'm not pulling. Like 10mpg bad. If I didn't work from home, I'd have traded it off already as it's that bad around down and on the highway.

I used to have a 05 Yukon XL Denali with the 6.0. That thing also had plenty of pulling power, but in 3rd gear rather than 4th all the time. It was quite a bit better empty and on the highway. I could usually get 15mpg out of it. I wouldn't have gotten rid of it, but the air ride was going bad, it had crappy 20 inch tires on it that were needing to be replaced, and I was right at the edge of my payload capacity with the "new" camper and my family is only getting bigger. I had a chance to straight trade for this 3/4 and took it. Honestly, I wish that Denali would have had more payload as that's why I ended up getting rid of it. Didn't want to spend a couple grand on tires and the air ride system, just to still have a vehicle that was maxed out, so I made the change.

I now I have a sledgehammer for a job that takes a regular claw hammer.....

[mkirsch]

The 2009 has to be a 2500HD, because as far as I know, GM stopped making the 2500 (non-HD) and 1500HD models well before 2009.

You will enjoy the towing power of the 8.1L for sure, but you will not enjoy having to stop for gas every 150 miles with the 25 gallon tank. Figure about 8MPG towing, but you will be keeping up with traffic.

[rjstractor]

I thought the 1500 Max Tow had a 6.2, not a 6.0, but I do remember now that the 1500HD was crew cab short box only.

[Need-A-Vacation]

I am guessing the '09 is a 1500 Max Tow truck w/ the 6.0, not the 1500HD (crew cab only). If so, it depends more on how much you can keep your foot off the accelerator of the 6.0/ 1500 vs the 2500! Lol

I would think the 6.0/6spd would do a little better from what I have read about the 8.1.

Good luck deciding!!!

[ktosv]

That 2001 will have a 5 speed Allison won't it?

Are you concerned about towing or non-towing mileage?

From what I have read, towing mileage will be similar. Non-towing the 6L/6 speed will be far better. At least the 20% that carringb mentioned if not more.

[rjstractor]

Is the 2009 with the 6.0 a 1500HD? IIRC the 6.0 was not available in a standard 1500. If it is a 1500HD, that would be a good fit for your trailer. The 1500HD is 8600 GVWR with 8-lug wheels, 6000 lb RGAWR, same specs as a pre-2001 2500. If it is a standard 1500, you'll be no better off than with your current tow vehicle.

[Randu]

I had a 2001 and a 2004 8.1 crew cab with 4:10 rear end. Both were pulling beasts as I pulled 14,000# 5th wheel with the 2001 and a 16,000# with the 2004. 9 mpg empty around town, 12 best case on hwy empty, and 7.5-8 towing level with minimum wind. Dropped to 6.5 on windy days. I ran 65-70 all the time and kept the 2004 10 years and 150,000 miles. Now have a 2014 Duramax and get 11-12 towing, 15 around town empty and 19.5 empty on hwy. The 6.0 should do a good job for what you intend to do with better everyday mileage. Randu

[carringb]

A 6.0 with the GM 6-speed seems to get about 20% better fuel economy unloaded than the 8.1L. But the difference is smaller when towing. There's so few 8.1L 6-speed allisons out there, I've never actually heard an owner's experience. The 5-speed Ally has about the same OD as the 4L85 so highway fuel economy will still be terrible.

For 7,000 pounds, the 6.0 should perform well enough, with the 6-speed at least. I was not a fan of the 6.0/4-speed combo. Too much spread between the gears.

[ktmrfs]

around town or running empty the 6.0 is going to be way better on fuel economy than the 8.1. And from friends that have had the 8.1, It may be worse than the 6.0 towing.

As for towing, the 8.1 is a workhorse, but I don't know if it will really outpull the 6.0. Hopefully someone who has had both can provide some good comparison towing.

[TerryandKim]

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