[crkoester]

After searching the internet unsuccessfully for the last hour for this info, I thought I'd drop a post here.

Anyone have any idea what kind of gas mileage you can expect out of the GM 8100 truck engine?

I'm looking at a 2001 GM Yukon XL 2500 with this big-block engine (mainly because it also has the HD Allison tranny - I've replaced the tranny on my current small-block 1500 3 times in 155K miles and I don't care to go through that again).

But I can't seem to find a straight answer regarding fuel economy on this monster - apparently the EPA doesn't give ratings to the big truck engines (I suppose they might have bad dreams if they did).

Can anyone give me an idea about this, or their own experience with this engine?

Thanks!


Chris

[RS 455]

In a GMC 2500 (2004) extended cab short bed 4x4 it gets around 12 mpg around town. Rear ratio unknown but standard for the truck.

[mzbk2l]

RS455 has the mileage for the 8100 about right, but I have a question about the original post: The Allison was not offered in the Yukons, Tahoes, Suburbans, etc.... They got the detuned version of the 8100 with a 4L80E transmission.

[crkoester]

It looks like you are right - no Allison trans for that Yukon. It IS being advertised as having the Allison tranny, but it appears the dealer is probably just clueless.

Well... that answers THAT question for me - without the Allison, I don't want it.

Thanks a bunch! That's great info... once again, the PY forums save the day....


Chris

[455Grandville]

Get a diesel, it'll outpull that 8100, and get better fuel economy. For 07 Dodge is supposed to have a new tranny thats up to the task (finally)
Just my .02

[Catalinaragtop]

I had a 03 Suburban 2500 with the 8100 Vortec.

Hauling nothing around town I'd get 10-12 MPG stop and go.

Hauling my 24 Ft. enclosed car hauler with my 61 Poncho ragtop I'd get 7-9 MPG driving 70-80. Trailer w/car weighs 7500-8000 pounds

On hiway with no trailer I'd get 14-16 MPG.

The 8100 has lots of guts for hauling.

I just got a 07 Suburban 3/4 ton with 6 liter engine.

I've got 800 miles on it .

Driving empty ( we live in rural Montana) I'm getting 16-17 MPG.

I hauled my trailer and car to West Yellowstone for "Rod-EO" and averaged 8.3 MPG driving 65-70 and it's a long cllimb to W. Yellowstone.

So far I'm satisfied and mileage should improve with more break-in.

Hope this helps.

Larry

[Catalinaragtop]

My 8100 would pull as well as a stock diesel. And no smell! Also, the $4k premium takes a lot of juice to make up when diesel now costs more than gas.

Good luck

[David Holmberg]

The 06 Allison is a 6 speed, it's a 2nd OD that really helps with RPM's and MPG.

[455Grandville]

A 8100 cant hold a candle to a Duramaxx for towing (650 ft pds vs 455 ft pds) or a Cummins (610 ft pds). 18 wheelers weighing 80,000 lbs can hit 7 - 8 mpg. Then try putting 500,000 miles on a 8100 without a rebuild, thats where a diesel pays off.

[Catalinaragtop]

Hey, I was just relaying my experience with the 8100. I trade every 3 years so would never hit o-haul mileage.
Do the math on gas vs. diesel at TODAY"S fuel prices, you might be suprised.

Also, I only tow about 20 percent of the time so I'm happy with what I have.

Thanks for criticism!!!!!!!!!!!!!!

[David Holmberg]

The 8100 is a great motor, and does pull very well.

The Duramax is $4000 more when you buy, and yes Diesel is slightly more around here. $2.95 for regular Vs $2.97 for Diesel. So the argument is always, "sure you'll get better MPG, but look how long it will take to recoup that money." That's true, however when you go to sell the Diesel motor will make the resale value more than $4000 higher than the 8100 or the 6.0 motor, so it's a win- win, if you can swing it at purchase time.

Like I said one of my racing buddies has an 02 2500HD with the 8100 and he loves it. He swore up and down that he could tow right with me (he has a 24 ft, mine is a 28) but the first uphill on ramp I put over a 1/4 mile on him... He never said anything about it again...

The 6.0 is also a Great motor with a ton of aftermarket parts available.

[455Grandville]

Originally Posted by Catalinaragtop

Hey, I was just relaying my experience with the 8100. I trade every 3 years so would never hit o-haul mileage.
Do the math on gas vs. diesel at TODAY"S fuel prices, you might be suprised.

Also, I only tow about 20 percent of the time so I'm happy with what I have.

Thanks for criticism!!!!!!!!!!!!!!

If you all get 16 mpg, Id say thats pretty good. Most diesels might (might !) hit 20. Then in your case, you got me there. Im suprised the 8100 hits that, I know the 90s 454s wouldnt do 16. The one good thing about the 8100 despite many changes from the old '54 is its still a proven design.

[mzbk2l]

The 8100 is a whole different animal than a 454. It's a clean sheet design that basically uses the same dimensions. Different crank, different firing order, different heads, etc.

For mostly driving around town, I definitely prefer the driveability of the 8100 over the diesel. I'd have to tow a heavy load pretty frequently before I'd prefer the diesel. (And yes, I've driven both VERY extensively, since several years before they went into production.)

[455Grandville]

The rods are longer also (6.135" vs 6.75) but its still based on the big block Chevy, heres something off the website : (Ive seen both the bare blocks only minor changes the 8100, they probably changed the coolant patterns again !))

The 8100 was borne out of GM Powertrain’s earlier 7400, the familiar and ubiquitous 7.4-liter V-8. The 8100, which displaces 8.1 liters, shares the same bore as the 7400: 4.25 inches. A longer stroke, 4.37 inches compared to 4.00 inches, gives it the added displacement. This is an unusual strategy in high-performance engines, where increasing bore is the preferred method, but GM chose it because a longer stroke typically translates into more torque and better durability.

[Coollx]

If your decision comes down to the 6.0 or the 8.1, get the 8.1. The 8.1 gets the same mpg but will give you more torque and towing power. An 8.1 with a 4:10 axle ratio makes for a very nice tow vehicle.

[RamAirZ]

Originally Posted by crkoester

It looks like you are right - no Allison trans for that Yukon. It IS being advertised as having the Allison tranny, but it appears the dealer is probably just clueless.

Well... that answers THAT question for me - without the Allison, I don't want it.

Thanks a bunch! That's great info... once again, the PY forums save the day....


Chris

May I ask why? The Allison tranny offered in our pickups isn't that great. It's an Allison name on a GM transmission, they aren't near as strong as the older Allison transmissions that people think of. Now don't get me worng they are good, just not AS good. Now the 4L80E is a strong beast. If you check out the LS1Tech board, alot of the guys running 9's and 8's are switching to a 4L80E. It's basically a TH400 with an overdrive. Alot of the parts are interchangable (at least on the early 4L80E's). They can take alot of abuse straight out of the box and last forever. Parish's 9 second pickup is running a 4L80E, Launching in 4WD and spraying it. I know he was running 10.0 on a stock trans with a shift kit and converter, not sure if it's stock still lol.

[Thumpin455_GTO]

Its been a few days but I just saw this.. We have some Duramax urged trucks with the turbo, all are 4x4, one is 3/4 ton the other two are 1 ton. One is dually one isnt. The one that isnt is an 06 and has the 6 sped trans in it, it pulls like nothing I have ever driven.

The 04 3/4 ton has gotten an average of 22 mpg while pulling my cars from South Carolina, to Michigan, and even to Nebraska. It pulled up all the hills going into Atlanta without a problem, didnt even have to downshift. My gas trucks cant come close to that mpg, even when empty.

All of the diesels are stock, never been modified in any way. Well worth the extra cost at buying time. GM has me sold on the Duramax..

My brother has a Dodge 1 ton dually with the cummings, he is lucky to get 16 driving around empty. Go drive one, pull something with it up a steep grade and see the difference. Around here diesel is cheaper than gas... but we are often as high as California and other insane places to get fuel.

[kni]

GM is weird. They will put a allison in the Yukon with the 8100 but wont put it in the 8100 Avalanche's. I've seen the 8100 Av's get anywhere from 12-14 mpg so I guess it would be simular to the Yukon's

[David Holmberg]

kni, The Yukon didn't get the Allison, the 8.1 got the 4L80E in the suburban and Yukon's. I'd be all over a Suburban with an Allison, and even better with the Duramax...