is there a significant difference

mrfishaholic · May 9, 2006

Ok, I am swapping in a 8.1L into my 2001HD crew cab 4x4. I have been told my auto trans that I already have is fine, and it will bolt right up. It is a 4 spd auto, is there a gas mileage difference with the allison? is there a conversion for the allison 4x4 to go from manual shift to connect to my electronic shift? I just bought a complete 2001 8.1L with auto tranny (allison) but it has manual shifter for transfer case, and I am wondering if there is enough differnce between the two trannys to even worry about the swap, or if there is a way to convert the manual 4x4 shift on the allison to a electronic shift. Thanks in advance guys!

Supercop8100 · May 9, 2006

The allison tranny is a BEAST. If you can in ANY way use the allison, DO IT. The extra gear is between first and second, so you wont feel much difference, kinda like a stepper gear. But the tranny is bulletproof. One helluva upgrade.

Shawn T · May 9, 2006

The 8.1L/Allison combo is available with an electronic shift T-case. The difference is big though. It is not an AUTO-TRAC active transfer case. That is what you have now. They use clutches/viscious coupling. The HD transfer cases for the DMax or Big Block are direct driven (chain or gear, I am not sure). I would not put the 8.1L in front of that T-case. The 4l80e should be OK. You will put a few more ponies to the ground. The HP losses with the Alli are a little higher. The SUV's that pack the big block use them (of course the HP and TQ #'s are a little less). On the other hand. If I were you, I would use the Allison and manual transfer case. The ruggedness of the Alli is miles above the 4l80e. On a side note; the final drive ratio of the Alli is higher than the 4l80e OD. This should result in better mileage. Plus you have a lower first gear and 5, instead of 4 overall gears. The Allison is a very, very nice addition. You will definately see a smoother power band.

Larry · May 10, 2006

Wow, you got a chore in your future if you really go through this. Not many people have the cohonies to attempt an engine swap such as this in a late model truck. These swaps are much easier going into older vehicles.

Did you get the ECM and Allison controllers as well as the harnesses along with the engine and trans you bought? There is a huge difference between the engine harnesses on 6.0 and 8.1’s. Did you get the 8.1L accessory brackets? Exhaust cross over pipe? Radiator? Have you compared part numbers of little things like the fan shroud, clutch fan, A/C hoses, etc? My experience has been to have a complete donor vehicle available before attempting a swap like this. Hope you have a friend in a GM dealer parts department and a bottomless budget.

The Allison would be nice but it would be much easier if you bolt this monster to your existing 4L80E and run it on a Suburban programmed controller (Suburban’s and Workhorse Custom Chassis P-chassis use 8.1L engines with 4L80E transmissions) so you won’t have to monkey around converting transfercases, acquiring the Ally controller and harness, etc. Regardless of manual shift or electric, the Allison and 4L80E have different output shaft spine diameters so either you will have to go with the better reliable manual shift that is currently on the donor engine/trans combo or go fish or an Allison version electric NV263 POS tcase.

I am actually allocating funds, collecting goods, and rearranging priorities to swap in an 8.1L into my 1978 K10 that has a 3 year old 4500 mile old 454HO carbureted crate engine. I bought a GM Marine EFI intake for it but have two slightly fangled up 8.1’s in my garage right now that might be easier to build than locate the marine controller, etc for the 454. One 8.1L is a 2001 (EGR/return fuel system) and the other is a 2005 (non-EGR, returnless fuel system). Once I get one of these engines built and before I buy my wiring harness I am trying to decide if I want to stick with my SM456 non-OD manual trans, fix and convert the Dodge variety NV4500 5 speed sitting in my garage to a GM main shaft or use a 4L80E that my buddy has laying around. Also have leads on a new production 4wd Ally LC1000 but cannot find a compatible tranfercase or adapter to make my NP205 work. I prefer a manual trans for this off-road, expedition, fishing truck. Hmmm….on second thought, maybe I want your manual shift NV261 and I can use a Ford Dana 60 left side drop axle to make it all work if I go the Ally route.

mrfishaholic · May 10, 2006

Oh, forgot that part, I bought a wrecked 2001 hd 2500 reg cab long bed 4x4, so I have a complete donor vehicle. Project is a ways off though as I am in baghdad right now. Probably get started on her in Dec or January with any luck.

I have the 2001 hd2500 cc sb, and with it I have the leather power seats with console, question though is how would I put the manual shifter in the floor? Can I keep the console?

Anyone going to need a complete 6.0 with all gizmos and gadgets (tranny and transfer case, fuel lines, fuel tank, computer, instrument cluster if wanted, etc in the Jan-Feb time frame? I will have one for sale, and you can come drive it before it is removed, just to verify the condition if you wish! - Will post this in the For Sale area later -

Ok back to the issue at hand, any other suggestions or comments? I have pleanty of time for everyone to provide advice as I have not taken on a project of this scale before. Willing to hear everyones .02 cents on what I should/ should not do, things to look for, cautions, warnings, etc.

Figured since I had the opportunity to get an 01 donor and mine is an 01 that I should have a better chance at a "smoother" swap/upgrade.

Bud · May 10, 2006

Oh, forgot that part, I bought a wrecked 2001 hd 2500 reg cab long bed 4x4, so I have a complete donor vehicle. Project is a ways off though as I am in baghdad right now. Probably get started on her in Dec or January with any luck.

I have the 2001 hd2500 cc sb, and with it I have the leather power seats with console, question though is how would I put the manual shifter in the floor? Can I keep the console?

Anyone going to need a complete 6.0 with all gizmos and gadgets (tranny and transfer case, fuel lines, fuel tank, computer, instrument cluster if wanted, etc in the Jan-Feb time frame? I will have one for sale, and you can come drive it before it is removed, just to verify the condition if you wish! - Will post this in the For Sale area later -

Ok back to the issue at hand, any other suggestions or comments? I have pleanty of time for everyone to provide advice as I have not taken on a project of this scale before. Willing to hear everyones .02 cents on what I should/ should not do, things to look for, cautions, warnings, etc.

Figured since I had the opportunity to get an 01 donor and mine is an 01 that I should have a better chance at a "smoother" swap/upgrade.

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