Looking for opinions!

[Effeckt]

SHORT Version - Swap my TH350 for a TH700R4 and keep my 350V8 or swap it all for a 5.3l V8 and 4l60 out of the newer model Chevrolet trucks?


I've been struggling to decide which direction I want to go with my K5. I have already decided that I am going to get a new transmission. The only I have currently (TH350) leaks big time and my mechanic basically said it needs a full on rebuild. It is not the transmission that I want since I do a fair amount of highway driving and so I originally planned to swap it for a TH700R4 rather than invest in the transmission that I don't really want anyways.

Lately I have been considering getting the 5.3l V8 with the 4l60 transmissions that accompany them in the newer model Silverado's and Tahoe's. It would give me the same end result but also give me better gas mileage while I am at it. Not to mention that my existing motor runs but not perfectly. It backfires occasionally and would need some work regardless.

I am not mechanical and would be farming out this work regardless of which route I go. I wanted to get everyone's opinion since I know a lot of you are more knowledgeable than I and some of you have even done this. Let me know what you think, pros/cons, etc. Thanks for all of your help. I love this forum and the ability to see what you all do and getting your expertise on this type of stuff.

[BOHICA]

Pound for pound, I'd much rather have a late model drivetrain (and intend to be going over to one), than the original, even with an OD transmission. However, remember that you'll also have to upgrade your fuel system and possibly your radiator, fab an engine crossmember, and deal with the wiring harness. If you get an aftermarket harness and PCM, plan to spend close to $1000 (if you're lucky). And then don't forget you'll almost certainly have to modify your driveshafts as well.

[Effeckt]

That's honestly what I have been thinking as well Bohica. I did not realize how much extra that would include me having to do however. I do already have a painless wiring harness in the truck so I might actually be good already there. Based on the other things you mentioned though, I might be getting in a little over my head as far as budget is concerned. I'll have to talk to some of the guys I know that do my work and see how much this kind of swap would look to set me back. If it gets too crazy, I may end up just sticking with the 700R4 despite my desire to go to the late model stuff.

[SeventyOne]

What's your budget? Can't tell you anything without a $ figure.

[rsavage]

If you have to farm all the work out the Ls swap will obviously be the more expensive of the two by at least a few thousands. Bohica was referring to the engine/transmission control harness and pcm not the truck's wiring harness. Don't know what gears you have in the differentials but if you don't have 3.07's you might have gear sets changed for a couple of thousand and improve your mileage somewhat. Even a 700 r is going to involve a trans/transfer case adapter, crossmember, drive shafts work etc. here is a sub forum that may help you:

http://67-72chevytrucks.com/vboard/f...play.php?f=206

[BOHICA]

Sorry, by wiring harness I meant the engine and transmission harness. If you can get one from the vehicle the engine came from, you'll be well ahead of the game. Ditto for the PCM. Supposedly, having those will make it a lot cheaper if you send them in to be modified for stand alone use, but I haven't seen any figures. Also, there are differences between Gen 3 and Gen 4 engines. They can interchange, but it takes some work.

I strongly recommend this book. It tells you everything you need to know. Good luck!

[Firebirdjones]

I did this swap myself last year (6.0/4L60E). It's not that bad, but is costly.

I was in the same boat, 350 turbo started slipping. It's my daily driver so immediately I thought about an overdrive. Even a swap over to a 700r4 isn't cheap since you'll need the adapters from Advance (about $800 for everything), you'll have to modify your shift linkage a bit as well as your tranny lines, TV cable bracket setup etc....

I personally wanted electronic control of my transmission (I don't like TV cables) and that meant a computer. So I thought I may as well get the engine to go with it and have the computer run all of it. So you can see how that whole domino effect came into play

You won't have to mess with driveshafts, the way around that is to move the engine forward about 1 1/2 inches, much easier.

It's really up to you, but the LS engine is the way to go in my opinion. Depending on how much you find a 5.3/4L60 combo for, the price of the swap will vary. It can easily top $5k start to finish. I did a few little odds and ends on mine to make it a nice factory looking swap and spent more than that, and that was doing all the work myself, but it gives you an idea. Hope that helps.

[BOHICA]

BTW, I'm planning on a Gen 4 5.3 and 6L80 swap in my Blazer, but had to put it on the back burner when I realized what all was involved. For what I spend on this, I could (or almost could) be up and running working on stuff in my own shop, so I've decided to go that route.

Here's a rough estimate. Keep in mind that this is pretty much all new stuff and not saving money by repurposing parts.

Aluminum 5.3 - $1200
6L80 - $1400
Circle pattern NP205 - $250
Radiator - $200 (I think one of those eBay specials would be fine in this case)
Wiring harness and PCM - $1000
Driveshafts - $300 ea. if using new ones (I figured if I'm doing it, I might as well do it right)
Fuel system - ??? Depends on whether or not you get a custom tank, use your old with a new sending unit, or what.
Crossmember - ??? Can't use conversion motor mounts because the LS oil pan won't clear the stock piece.
Brakes - You'll need new brakes if you're still running drums up front like I am.

So, right now I'm at $4650, and haven't even dived into the fuel system or small parts yet. However, keep in mind that using a Gen 3 engine that you can usually find for $500 and a 4L60 will be WAY WAY cheaper than what I'm doing.

[BOHICA]

Originally Posted by Firebirdjones

You won't have to mess with driveshafts, the way around that is to move the engine forward about 1 1/2 inches, much easier.

That's good to know.

[Firebirdjones]

Originally Posted by BOHICA

BTW, I'm planning on a Gen 4 5.3 and 6L80 swap in my Blazer, but had to put it on the back burner when I realized what all was involved.

Here's a rough estimate. Keep in mind that this is pretty much all new stuff and not saving money by repurposing parts.

Aluminum 5.3 - $1200
6L80 - $1400
Circle pattern NP205 - $250
Radiator - $200 (I think one of those eBay specials would be fine in this case)
Wiring harness and PCM - $1000
Driveshafts - $300 ea. if using new ones (I figured if I'm doing it, I might as well do it right)
Fuel system - ??? Depends on whether or not you get a custom tank, use your old with a new sending unit, or what.
Crossmember - ??? Can't use conversion motor mounts because the LS oil pan won't clear the stock piece.
Brakes - You'll need new brakes if you're still running drums up front like I am.

So, right now I'm at $4650, and haven't even dived into the fuel system or small parts yet. However, keep in mind that using a Gen 3 engine that you can usually find for $500 and a 4L60 will be WAY WAY cheaper than what I'm doing.

Not sure how the 6L80 will work, that thing is a monster. So you will definately have to move the transfer case back (ALOT) and that's going to add to the cost. I was going to use a 4L80E in mine, but it was just too big and I wasn't about to move the transfer case. That just opens an entirely new can of worms, cutting floor for shifter, possible console interference, possible exhaust interference (in my case) then a pair of driveshafts made at $300 a pop,,,so I bought a 4L60, simply moved the engine forward a bit, and the rest was cake.

You don't need an LS specific radiator, GM makes a hose that reaches from the driver side to the passenger side that was factory equipment on some of the first LS truck before a radiator change was made. So that's a simple solution there that saves some coin.

Fuel system, I'll eventually go with a custom tank with an in tank pump. Right now an inline pump does the job with a regulator. I made my own supply and return lines out of AN fittings and aerospace nylon braided hose so that was a bit pricey, about $500 when it was done. But it's cheaper than a high dollar in tank pump setup with a custom made tank ($1500 roughly is what I'm looking at).

Crossmember is made by Pacific Fabrication and is a simple bolt in. Complete with poly mounts, made for the LS swap in a 4x4 with clearance for the front differential. Worked great for me. I think I paid about $350 for that but it saves headaches.

Other costs like a custom made wire harness and computer. I went with Howell Engine Developments (used them in the past on other swaps) The harness is made specifically for the vehicle according to where you want to mount the computer. Harness is factory appearing with weather packs and all, with everything labeled, it's literally plug and play.
I also ordered a computer with a custom tune (that I tuned later for my own purposes), fuel pump and regulator, new 02 sensors, new fuel filter, and a few other little odds and ends and spent $1200 on that.

AC was another expense, relocation kit, compressor, new lines etc...about $500

It just goes on and on....

[Firebirdjones]

Another slick add on with the Howell harness I bought, if you use a drive-by-wire setup (2003 and up??) Howell can have wires coming out of the computer for cruise control, all you need is a simple button controller to wire up.

That's another consideration, if you go drive-by-wire, make sure you get not only the gas pedal out of that truck, but the control box as well. That gas pedal control box is about $500 for a new one if you need it. Howell supplies the harness for that as well included in my price I listed above.

Something else they did was make my harness with dual electric fan hookups. So I could rid the truck of the mechanical fan (clean up the engine bay and have more room) and I installed a dual electric fan setup out of a 4th gen camaro.

Since the 700/4L60's are considered fragile by some, I also built my 4L60E to hold (rated at) 600 hp because I have other plans for mine. That was another added expense. I really don't trust them much in stock form anyway.

[longbed67]

If your going to do a swap I would look for a late model lower mileage wrecked truck that you can pick up for a couple g's then you would have everything at your convenience and know your not missing anything... scap the rest and get a few hundred for it and call it a day.

[Firebirdjones]

So what do ya think so far Effeckt, have we scared you off from the swap yet?

[Effeckt]

Haha the amount of work doesn't scare me away but I definitely think the cost is more than I was looking to get into. I was basically curious if I would be able to get away with this swap for the ballpark of 5k. Not being able to do the work myself is probably going to double that cost so I've pretty much decided that the 700R4 is for me. Then I will address the motor that I've got which isn't bad, just isn't running as well as I would like. I do really appreciate all of the information you guys have given me. Really enlightening. I would love to do this swap but without the know-how, I just don't think it's a viable option for me.

[Effeckt]

So that being said.. my understanding with a swap like that is there is still a difference in about 2 inches in size between the two transmissions and that an adapter will be needed for the new transmission. Is there anything else involved or does that about cover it?