BBC 205 4l80e conversion

[Craig Nedrow]

I have a 1973 K20, 205, and am in the process of gleaning information for my swap. I bought the advanced adapters kit to couple the two wheel drive 4l80e to the 205. Without getting bogged down in all the details, I just had an idea, and am putting that out there to see if anyone has heard or done this. The 4l80e is approx. 2.5 inches longer then the 350. Install would require shortening the rear drive line, and lengthening the front the 2.5 approx amt. I am a retired journeyman machinist, with all the equipment in my home shop to make drive lines, so no problem. However If I made an adapter that bolted to the triangle bolt pattern of any SB or BB motor mount on the engine, (here is the kicker..), and moved the engine forward to accommodate the 2.5 difference, seems to me that would be a fairly easy way to do it. Trans lines would really be the only thing to change (I believe). Fan PS hoses, wiring and etc all looks like it will fit. At this point I am still gathering info, so pros and con's invited, as two or more heads are better then one. As a note, Like the Spartan locker article I recently did for the front D44 mod on here, I will do the same for this. I will finish the install, taking many pictures, pt numbers, and etc so ANYONE should be able to do the same, that's why we are here right, to learn, and teach. LMK Here is a link to the Spartan locker install.

1973 K20 front D44 Spartan locker install

This is basically a pictorial R&R of a Spartan locker into my stock open diff D44 on the 73 K20. So... Remove the tires, than all of the following will need to be removed: locking hub. disc brake calipers, bearing hub and finally the backing plate. As they are listed is how I removed them, this...

www.gmsquarebody.com

 

[Bextreme04]

I'm doing the same to mine. I'm trying to decide if I want to machine down the adapter index ring on my stock 205 or if I want to buy the advance adapter one. They used to make a 1" thick ring that just converted the TH400 index ring to the 4L80E index ring size, but it isn't made anymore.

Apparently no driveline changes are needed if going from a TH400, since overall length is almost identical. I think your only issue might be contact of the front of the engine with the front crossmember. You might also run into clearance issues with the exhaust manifolds or headers and the frame. You might be surprised and not need to do anything to the drivelines.

What controller are you using for the trans?

 

[Craig Nedrow]

Hey Eric keep me in the loop...I have two stock controllers, however they are both on engine/trans combos destined for other rigs. Since stock ecm are reasonable, and I have an HP programmer, I will probably go stock. We are getting int spring, which means lots of ranching chores, and am trying to get the 6.2 running, and etc, hope to have this done early summer and running.

 

[Bextreme04]

Hey Eric keep me in the loop...I have two stock controllers, however they are both on engine/trans combos destined for other rigs. Since stock ecm are reasonable, and I have an HP programmer, I will probably go stock. We are getting int spring, which means lots of ranching chores, and am trying to get the 6.2 running, and etc, hope to have this done early summer and running.

Nice, will do. I'm using an 0411 computer and a modified 2002 Silverado OS for now. I thought about getting HP tuners, but am using an OBDXPro VT tool and Tunerpro software for now to just mess around with it. If I can't get good results with that, then I will probably spring for HP tuners in the future.

 

[shiftpro]

I would never consider moving the engine forward, especially a big block. Squares are already disadvantaged with the weight bias and it's exacerbated with a BB.

 

[shiftpro]

Just a comment on the 205 transfer case.... highly recommend you look at converting to twin stick. If you do any kind of real work off roading or even highway winter ice conditions, you would have the advantage of running front wheel drive only. Works awesome on greasy mucky logging road switchbacks. Or off camber slick trails.

 

[shiftpro]

What controller will you use for the 4l80?

 

[Bextreme04]

What controller will you use for the 4l80?

It sounds like he's planning on just using a stock LS P01 or P58 ECU. They are only about $50 with pigtails included. You only need RPM, TPS, and ISS/OSS inputs for the 4L80E to run correctly on any stock computer. With HP tuners its stupid easy for him to just do a 4wd 4L80e OS transmission segment swap into any stock LS computer and run it regardless of the engine being run.

 

[Matt69olds]

I’m curious how you modify a stock PCM for a LS powered truck to run just the trans. I have a 4L80e built and ready to go minus a converter for my Olds. I’d be interested in learning what is involved in this conversion.

Im pretty comfortable with automotive electrical systems, and the proper wiring methods. Im not very good with computers, I need a 10 year old kid to show me how to do most things.

 

[Craig 85]

I agree with Shiftpro. I won't move the engine forward due to the weight bias. Since the transmission is longer than your TH-350, it would improve your front drive shaft angle ever so slightly. I know on my truck, even with only a 3" lift, the cardin joint looks close to binding if I real cross it up.

 

[Craig Nedrow]

Ok, looks like I got my answer from people I trust to be knowledgeable. It will only take a day in the shop to mod the d-lines, have a steady rest etc, and have done many, so know the procedure. Need to buy a longer piece of DOM for the front, should be able to get it locally, and of course I will take a bunch of pictures so others can see and know what is involved. Addressing the PCM, I will use, most likely a stock 886 or 411, plentiful and cheap. Will likely mod a stock harness, cheap and lots of info on the web. Reasoning, is that I want to learn, and also want to be able to fix anything on my truck myself. I love the 454, but it is a gas hog, and I am looking forward to doing down the road like a modern truck at 70 mph and 2200-2400 rpm, not the 3400 I am rinning now. The .75 od will make this truck much more user friendly, quieter, less tense. Have an LQ4 I am building, and toying with the thought...

 

[Bextreme04]

I’m curious how you modify a stock PCM for a LS powered truck to run just the trans. I have a 4L80e built and ready to go minus a converter for my Olds. I’d be interested in learning what is involved in this conversion.

Im pretty comfortable with automotive electrical systems, and the proper wiring methods. Im not very good with computers, I need a 10 year old kid to show me how to do most things.

If you get the PCM out of a 2500 that already ran a 4L80e... no modification is even necessary. You just don't use any of the engine parts of the ECU on an older HEI engine. You only need to feed the PCM Tach and TPS inputs. The ISS/OSS come from the trans harness side. All of the other sensor inputs and stuff on the PCM are only needed for running the engine, and since you won't have the engine run by the PCM, they don't matter. If you have a tool capable of communicating with the LS computer like HP tuners or an OBDXPro VT or OBDLink, you can use HPtuners, PCMHammer, or LSDroid to write any OS you want onto any of the PCM's.

If you choose one of the popular OS's like 12587603, 12208322, or 12212156 you can get an XDF file for them that will let you modify all of the parameters in TunerPro. If you have HPTuners of course you don't need any of that. You just plug it in and pull something off the tune repository that will work.

You can use BlueCat trans tuning software to figure out proper shift parameters and then just plug them in to the PCM if your gear ratio and such are different than the stock tune.

 

[Craig Nedrow]

Thanks Eric! I have two 4l80E's 1999, 2006, two PCM one that is wn the LS1/t56, and one on the LQ4/4L80E, both 886 or 866? I also have a late model HP tuner, and am learning. I do not want to rob the motors I have as they are destioned for other greatness in the 64 nova, and 54 3600. So need to pick up a harness and PCM. My thoughts.

 

[Bextreme04]

Here's a guy that did exactly what we are talking about on sloppy mechanics. The HPtuners credits and PCM/harness ends cost him $125

https://sites.google.com/site/sloppywiki/everything-ls/cheap-stand-alone-trans-controller