LS to TH400

[Psycho71]

Hi All,

I have done some searching, and cannot run across the info I seek w/o interpreting excerpts from several other threads to arrive at a conclusion. I'd like to see if I can get some straight up answers to the questions I have before I start assembling info that might or might not be completely accurate for my application.

I have an '85 K20 Suburban. Good running 350, th400 trans, w/NP208 transfer case. Fuel is eating me alive, and I have another project in which the 350 could be of good use. So I am looking at my options on either a diesel, or an LS swap. Diesel has it's appeal, but too in depth for a diesel that will make any larger amounts of torque. So the LS swap is what I'm looking at now. Mostly looking at the 5.3 liter.

I am wanting to continue using my transmission, transfer case, and remaining drive-line parts. All are in great condition, and do not need any work.

* What is involved in connecting the LS engine to the th400?
* Any controllers, sensors, add-ons of any kind I'd have to run to make these two jive together?
* Will my mounting points stay the same? Crossmember mainly?
* Will I be able to re-use the torque converter I have now?

On the LS swap itself;
* Any comprehensive lists, part numbers helpful, that reflect the necessary items I would need to swap an LS into my burb?
* What is everyone doing about guages when doing an LS swap? not really looking to go all out wish the new dash components and all that. Just want an EFI engine with good reliability.
* Will there be any issue with running my trans, speedo gear, with the cable as OEM equipped? Or will the LS engine/ECM need some kind of signal input for this?
* What all would I need off the donor truck to complete this swap as far as I possibly could? Yes, i want to go back with the EFI as well.
* Any issues I might not be looking at that I should be?

I'm not looking to modify the LS engine any at all, at this point. Looking to keep the swap as simple as I can, as economical as I can, and as reliable as I can. I know w/o the OD trans, my mileage will suffer a bit. But compared to what I'm getting now, it can only improve. Mianly I want something in there with a decent amount of torque, reliability, and a few more MPG's than I get now.

Thanks for any help or insight y'all can provide. I am an old school gear head myself. The new platforms are a bit foreign to me, but more than willing to learn about them.

Thanks for you time and patience.

[skoffice]

TCI makes an adapter flex plate to go the the TH400. I think it runs about $200. Shouldn't need to touch the trans other than the kick down linkage, you will have to fabricate something to connect it to your throttle body on the 5.3. Best bet is to get a harness that's already done. I like to use Howell but there are many other good sources out there as well. Would not recommend painless. Mounting points should be all the same, and factory gauges can all be used. Fuel system will need to be upgraded to high pressure electric pump with regulator and return line to the tank. I'm using a walbro 255lph pump and it works great and it's fairly cheap.

[Psycho71]

Cool, the kickdown on the TH400 is electric,a nd would be easy to modify if needed.

From what I have read, I will be going with a prebuilt harness.

Fuel system upgrade would be easy too. Already have a return line, so it'd just be a matter of slapping the pump inline, and going on with it.

All this sounds encouraging for sure. I'm thinking I have a good wintertime project in the works with this one. Until i get a little farther along, I'll stay tuned in here and learn what I can so I'm not asking more stupid questions than I ordinarily would.

[Shon]

I have the TCI unit listed here for $230, I can ship it to you for $215 if interested: https://www.herronperformance.com/st...&productId=403

Some use their stock flexplate and elongate (sp) the holes slightly and use this spacer:
https://www.herronperformance.com/st...&productId=239

[Psycho71]

Cool, Bookmarked the site. Will be in touch when I start amassing parts for the swap this winter. First thing will be to find the donor, and get the engine w/ECM, and all the goodies still attached.

[Super73]

In my opinion, a well dialed in Carb will produce similar milage as a fuel injected motor (this coming from a guy that thinks LS motors should be in everything). Now, I think the biggest improvement possible are with aero, driving habits, an overdrive, electric fan, motor, not to mention weight and drivetrain.

I think if you bought a wideband, learned how to dial your carb in, you would be ahead financially and time wise.... But.... LS motors are awesome. Do yourself a favor and put an OD trans in at the same time if you do the swap.. Well, if you are going for milage.