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GM 8.1/Allison transmission

Old 05-23-2019, 11:49 AM
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Default GM 8.1/Allison transmission

Got the chance to drive an '01 2500HD with the 8.1/Allison in it.

Can't lie one bit, those things have some POWER. They have some serious low end torque for what they are. You can tell GM built that thing to be a big ass gas motor that had similar power to the LB7. Very impressed, and I'd definitely own one as a second truck!!!!
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Old 05-23-2019, 11:53 AM
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Originally Posted by Manoverboard123 View Post
Got the chance to drive an '01 2500HD with the 8.1/Allison in it.

Can't lie one bit, those things have some POWER. They have some serious low end torque for what they are. You can tell GM built that thing to be a big ass gas motor that had similar power to the LB7. Very impressed, and I'd definitely own one as a second truck!!!!
We have a lot of small cattle & hay farms around here. Lots of folks still driving 8.1's and For V10's. Perfect power plant for the guy that tows heavy and frequently, but without any real distance or speed. The diesels are wonderful, especially when you do a lot of miles. But for the guy that is doing 5,000 - 10,000 miles a year, simple and strong makes a lot of sense. A lot like a regular cab half ton, or something similar to a Tacoma for knocking around the farm in, and use the big trucks exclusively for heavier work.
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Old 05-23-2019, 11:55 AM
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Originally Posted by Manoverboard123 View Post
Got the chance to drive an '01 2500HD with the 8.1/Allison in it.

Can't lie one bit, those things have some POWER. They have some serious low end torque for what they are. You can tell GM built that thing to be a big ass gas motor that had similar power to the LB7. Very impressed, and I'd definitely own one as a second truck!!!!
better own a gas station as well!
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Old 05-23-2019, 11:57 AM
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plenty of motors make just as much or more power than a diesel, the problem is you have to whined it up to get that heavy load moving!
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Old 05-23-2019, 12:03 PM
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Originally Posted by Rolandt03 View Post
plenty of motors make just as much or more power than a diesel, the problem is you have to whined it up to get that heavy load moving!
Not the 8.1. They have tons of low end grunt. Get absolute garbage for mileage, but for a low mile driver mileage basically doesn't matter.
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Old 05-23-2019, 12:18 PM
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8.1's get gallons per mile!
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Old 05-23-2019, 12:27 PM
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Originally Posted by autobaun70 View Post
Not the 8.1. They have tons of low end grunt. Get absolute garbage for mileage, but for a low mile driver mileage basically doesn't matter.
ours had alot of low end grunt, but when hooked to the 35ft flat bed she didnt move until she was spinning pretty good!
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Old 05-23-2019, 01:26 PM
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I had an 8.1 and that trucked pulled like mad. But sucked gas to do it. I loved that truck. Compared to the diesels in the day they were very affordable.
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Old 05-24-2019, 06:07 AM
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They are unicorns- sort of. Great vehicles. About 11 mpg....
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Old 05-24-2019, 06:51 AM
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They were like an LS big block. There is an enginemasters (motortrendondemand.com) episode where they tested a classic big block chevy low deck that blueprint engines made in a 598 to drop in where a 454 was. Had like 700 lbs-ft at any rpm with stock style iron $500 heads.

https://blueprintengines.com/product...rtblock-ps5980

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Old 05-24-2019, 02:41 PM
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I had an 02 with the 5 spd Allison. It pulled good used a ton of oil and gas when under a load. Traded it for an 07 cc 4x4 dmax with 6sp no comparison. On a side note I got 14 k trade in for that truck with 80 k on the clock it had leather and really nice truck. It was 5 years old. My 07 was just totaled last month had 168 k on the clock and I got 21860. From insurance. And I believe it was a 25 k truck. Amazing how diesel holds value
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Old 05-24-2019, 05:23 PM
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I had an 06. Got 10mpg. Sold it with $286K. Still ran new and didn't leak a drop of anything. Tons of power. Now I drive a 4.3 1500. I get 21MPG.
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Old 05-25-2019, 07:45 AM
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As noted, really strong engine and transmission combo. Could pass anything but a gas station...
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Old 05-25-2019, 06:02 PM
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Originally Posted by Rolandt03 View Post
better own a gas station as well!
8mpg 6 towing
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Old 05-26-2019, 06:42 AM
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I have an 02 as a second truck and love that thing! It's definitely a beast of a truck, pulls my boat around without even thinking about it. Never met a gas station it didn't like. Guess that's why I only have a 104,000 miles on it. If you have the chance to buy one get it.
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Old 05-28-2019, 05:49 AM
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Originally Posted by oceandansar View Post
I had an 02 with the 5 spd Allison. It pulled good used a ton of oil and gas when under a load. Traded it for an 07 cc 4x4 dmax with 6sp no comparison. On a side note I got 14 k trade in for that truck with 80 k on the clock it had leather and really nice truck. It was 5 years old. My 07 was just totaled last month had 168 k on the clock and I got 21860. From insurance. And I believe it was a 25 k truck. Amazing how diesel holds value
it really is stupid. gave 22k for a 07 classic duramax with 111k miles on it in 2011, could sell that truck now with close to 240k for probably 18-19k
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Old 05-28-2019, 11:28 AM
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Just filled up my 2500 Burb with the 8.1, that tank averaged 8.5 MPG. Donít have the Allison tho, couldnít get it in the Burb. 8.1ís are getting hard to find. Blew my original 8.1, went looking for a reman. GM Goodwrench couldnít give me a timeline b/c they didnít have a block, same story from some other reman outfits. They say that block isnít being cast anymore. Finally got one from Jasper, not cheap
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Old 05-29-2019, 11:34 AM
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I had a 2005 GM 4x4 crew cab long bed LT dually with that combo. PO put flow masters on it. It sounded great except when it was towing. the drone became mind numbing and the stiff rear suspension would jar your teeth loose . Otherwise it was a beauty. I eventually moved up to GMC with the Duramax. Pulling a 27' Pursuit the 8.1 got around 5 mpg towing. Duramax saw 12 mpg and never missed a beat doing it.
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Old 05-30-2019, 04:27 AM
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My 2500 Avalanche w/ 8.1 and 4.10 axles got 8-9 pulling my Chris Cat. No Allison trans. Had Flowmaster BB70 2 in 2 out muffler and dual tips. She purred a deep rumble.

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Old 05-30-2019, 06:20 AM
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Originally Posted by Pursuit1 View Post
I had a 2005 GM 4x4 crew cab long bed LT dually with that combo. PO put flow masters on it. It sounded great except when it was towing. the drone became mind numbing and the stiff rear suspension would jar your teeth loose . Otherwise it was a beauty. I eventually moved up to GMC with the Duramax. Pulling a 27' Pursuit the 8.1 got around 5 mpg towing. Duramax saw 12 mpg and never missed a beat doing it.
the exhaust droning in the cab is obnoxious as hell! id have the exhaust reworked as soon as possible! gets old real fast!
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