LSA/6L90 Alpha swap - Hummer Forums - Enthusiast Forum for Hummer Owners


Hummer H3 For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.

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Old 12-29-2017, 12:34 PM
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Default LSA/6L90 Alpha swap

I'm getting ready to start building my brothers H3 Alpha and I have some questions for you guys.

First off I'd like to say that I'm not new to swapping engines and I've done a lot of research so far but can't seem to find some information. I do realize that this is going to be a huge project, and will cost a lot of money so no need to send out the warnings.

I'm building the Alpha instead of selling it and buying an I-5 basically because I don't want to deal with the headache of it. Plus the paint matches his Harley and the leather is in really good shape.

The reason behind going LSA instead of LS3. I've been doing the research for this project for about 6 months. I want this to be a torquey fun to drive engine and since I can guy a low mileage LSA pull out for about the same amount of money as a crate LS3 I figured why not. Since I won't have a shop install the engine I wouldn't be able to have the warranty.

I'm still trying to figure out if I will run the 6L80 or 6L90 (Really haven't got the chance to measure around and see how short the driveline would end up with the 90) but I want the 6 speed and don't want to be going through 4L65s every other year. I will be keeping it DS drop for the transfer case for the upcoming axle swap. Since it will be a drivers side drop it will be easier to get a HP housing.

My questions are:

Is there any demand for an Alpha engine/trans/transfercase?
I know that the Alphas have a steel diff housing for the front so are those also desirable?
Is the BCM going to be an issue with running the 6L80-90? from what I've read I can flash the ECU with the files to run the engine and transmission (with the proper wiring harness) but with out the buttons for the TU/TD is this going to cause a HUGE headache for me? I'm trying to not have to buy an interface basically.
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Old 12-29-2017, 05:03 PM
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Join Date: May 2008
Location: Shrewsbury, MA
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Quote:
Originally Posted by Blueoval_boy_64 View Post
I'm getting ready to start building my brothers H3 Alpha and I have some questions for you guys.

First off I'd like to say that I'm not new to swapping engines and I've done a lot of research so far but can't seem to find some information. I do realize that this is going to be a huge project, and will cost a lot of money so no need to send out the warnings.

I'm building the Alpha instead of selling it and buying an I-5 basically because I don't want to deal with the headache of it. Plus the paint matches his Harley and the leather is in really good shape.

The reason behind going LSA instead of LS3. I've been doing the research for this project for about 6 months. I want this to be a torquey fun to drive engine and since I can guy a low mileage LSA pull out for about the same amount of money as a crate LS3 I figured why not. Since I won't have a shop install the engine I wouldn't be able to have the warranty.

I'm still trying to figure out if I will run the 6L80 or 6L90 (Really haven't got the chance to measure around and see how short the driveline would end up with the 90) but I want the 6 speed and don't want to be going through 4L65s every other year. I will be keeping it DS drop for the transfer case for the upcoming axle swap. Since it will be a drivers side drop it will be easier to get a HP housing.

My questions are:

Is there any demand for an Alpha engine/trans/transfercase?
I know that the Alphas have a steel diff housing for the front so are those also desirable?
Is the BCM going to be an issue with running the 6L80-90? from what I've read I can flash the ECU with the files to run the engine and transmission (with the proper wiring harness) but with out the buttons for the TU/TD is this going to cause a HUGE headache for me? I'm trying to not have to buy an interface basically.
We have been in the process of doing a 6.0L/ 6l90 swap since the summer...not easy and if I did it again I would probably have done a 4l80 swap if the length cleared the torsionbar crossmember. The 6l90 is too long and will push the factory transfercase well into the torsionbar crossmember which is a structural crossmember welded to the frame so your only choice is to come up with a wiring harness and custom manual T-case shifter for a np241 or atlas or just run a built 6l80 which is about $5k-6k The only other H3 out there with a 6l80 that runs does not have proper programming or wiring harness so the torque converter does not lock in 4lo, have accurate speedometer or have proper shift tables in 4lo. To do it right will require a different wiring harness that has accommodations for a custom external reverse switch (cost us close to $400 for a one off) due to the BCM on the H3 not being able to receive the reverse signal from the T-43 in the 6l80/90. Hopefully we will be up and running around end of February.
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Old 12-30-2017, 01:44 PM
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Originally Posted by atvspeed4 View Post
We have been in the process of doing a 6.0L/ 6l90 swap since the summer...not easy and if I did it again I would probably have done a 4l80 swap if the length cleared the torsionbar crossmember. The 6l90 is too long and will push the factory transfercase well into the torsionbar crossmember which is a structural crossmember welded to the frame.
do you have any pics showing how close to the crewmember it comes?
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Old 01-02-2018, 01:59 PM
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Location: Shrewsbury, MA
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Originally Posted by Blueoval_boy_64 View Post
do you have any pics showing how close to the crewmember it comes?
Sorry no pictures. Its not a matter of it coming close, a good couple inches of the factory transfercase would be in the crossmember. Since you are running a driveside drop you will be using some other transfercase so its a moot point
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Old 01-12-2018, 08:54 AM
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Join Date: Sep 2012
Posts: 105
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Quote:
Originally Posted by Blueoval_boy_64 View Post
I'm getting ready to start building my brothers H3 Alpha and I have some questions for you guys.

First off I'd like to say that I'm not new to swapping engines and I've done a lot of research so far but can't seem to find some information. I do realize that this is going to be a huge project, and will cost a lot of money so no need to send out the warnings.

I'm building the Alpha instead of selling it and buying an I-5 basically because I don't want to deal with the headache of it. Plus the paint matches his Harley and the leather is in really good shape.

The reason behind going LSA instead of LS3. I've been doing the research for this project for about 6 months. I want this to be a torquey fun to drive engine and since I can guy a low mileage LSA pull out for about the same amount of money as a crate LS3 I figured why not. Since I won't have a shop install the engine I wouldn't be able to have the warranty.

I'm still trying to figure out if I will run the 6L80 or 6L90 (Really haven't got the chance to measure around and see how short the driveline would end up with the 90) but I want the 6 speed and don't want to be going through 4L65s every other year. I will be keeping it DS drop for the transfer case for the upcoming axle swap. Since it will be a drivers side drop it will be easier to get a HP housing.

My questions are:

Is there any demand for an Alpha engine/trans/transfercase?
I know that the Alphas have a steel diff housing for the front so are those also desirable?
Is the BCM going to be an issue with running the 6L80-90? from what I've read I can flash the ECU with the files to run the engine and transmission (with the proper wiring harness) but with out the buttons for the TU/TD is this going to cause a HUGE headache for me? I'm trying to not have to buy an interface basically.
i recommend you opt out of the LSA and just get an LS3. Unless you are planning to run 40s or regear your axles to 3.xx, the 550 tq LSA plus that 4.03 ratio first of the 6L80/90 you will be for sure doing 2nd gear starts (even 3rd gear).
Im running a cammed LS3 at 485 tq and flooring it from a 20 mph rolling start is extremely hard to control (with 35s and a 4l60e). I cant imagine running 65 more tqs coupled with that 1st gear of the 6l80e.

I currently wait for my truck to shift to 2nd before I give it more than 50% throttle. I am planning on getting 37s once my 35s wear out and I am hoping the reduction in gearing will be enough to allow the truck the handle better in 1st.

whatever you do, keep us posted. It will be one hell of a truck!
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