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Thread: Official NBS 4.3v6 to GEN 3 V8 swap Guide

  1. #1

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    NBS V6 to V8 Swap

    So basically youíre tired of going slow and want some power and obviously you want to swap out that old 4.3 for that massive V8 so letís get to it. There are some other threads out there but they arenít really informative because most people have a shop do the swap unlike me who did the swap myself with a few friends.

    What do I need?
    You need the engine of course, the motor needs to be complete.
    Complete means 100% ready to bolt in and fire up. It needs to look like this

    It needs the wiring harness from a V8 Silverado, if you have a 99-02, get that harness if your motor is 03+ be sure to get a harness for an 03+ reason being the 99-02 models have a drive by cable throttle body and the 03+ models has the electronic throttle body.

    Manifolds: the hell with manifolds get you some long tube headers and custom exhaust.
    Pacesetters are great for the price. You can reuse your stock manifold bolts and gaskets off the v8 motor if your new motor came with them.

    PCM- AKA the computer- The V6 PCM is the exact same externally as the V8 PCM the only difference is the tune or program that is written to the PCM. So you will need to have your V6 PCM reflashed and tuned with the V8 parameters. I would recommend Nelson Performance. http://www.nelsonperformance.com
    Allen will send you a PCM tuned for your new motor and mods in which you have installed. The tuned PCM will also be tuned for the V6 Vin # so everything will fire up on the first try if everything is hooked up correctly. Once you receive the new PCM simply send Nelson Performance your stock V6 PCM. Nelson Performance is not the only option, there are some other options such as custom DYNO tuning or other mail order tuners. Just be sure to ask whoever does the tuning if they can indeed reflash the V6 PCM with the V8 parameters and V6 vin.

    Transmission- The V6 transmission will bolt up but it will live a short life behind the new powerplant. I would recommend purchasing a built unit from a reputable Transmission shop such as FLT (Finish Line Transmissions) http://www.finishlinetrans.com/
    FLT builds flawless units everytime and they dyno test them before shipment. Chuck or Vince can recommend a specific model for your needs.
    Note: the stock V8 unit will break just as fast so get a good built unit that will suit your needs.

    Torque Converter:
    A stock V8 converter will work but the whole purpose of this swap is for power right?
    A torque converter alone can knock off a Ĺ second off of your ET.
    Vigilante and Yank build good stalls, They can recommend a stall speed for your application and mods.

    Flexplate- You will need a 4l60e flexplate from a V8 motor, a stock one should work fine.
    Note: If you purchased a 6.0 and it has a flexplate on it already it probably will not work because the engine was most likely mated to a 4l80e transmission.
    Fan shroud: you will need a v8 fan shroud if you plan on using the clutch fan, BTW now is a good time to upgrade to E-FANS!!! If you do upgrade no shroud will be necessary.

    Motor mounts: unfortunately the stock mounts will not work. You will need to purchase 99-03 Ĺ ton frame mounts and engine mounts, you can get these at your local chevy dealer or find them from a salvage yard.

    Hoses: you will need 99-03 radiator hoses- upper and lower, AC hoses, Heater hoses,

    you will also need a nipple that connects to the back of the intake manifold that provides vacuum for your brake booster, the 6.0 engines power breaks use their power steering pump. you can get this from the dealer or off a 4.8,5.3 intake manifold.

    Radiator: yes your stock v6 radiator will work, the only difference between the 28Ē v6 radiator and the 28Ē v8 one is one small connector that returns coolant back to the radiator from the throttle body, search TB bypass for more info. Simply install a T on the hose coming from the radiator reservoir that runs to the radiator and connect the line from the Throttle body or block (if you bypassed) to the T fitting. Be sure to use hose clamps to insure no leaks.

    Air Intake: the air intake setup on the V8 engines are completely different than the v6 setup, you can purchase a stock unit or replace with an aftermarket setup. FYI you can also do a search on the board that will inform you of what you will need and where to buy specific parts to build your on Cold air setup that will compare to the best aftermarket ones.
    Note: the stock box will work you just need the tube.
    The stock MAF (mass air flow sensor will work as well)

    Fuel Lines: The stock fuel lines will not work with the new motor, you will need

    2 EAR-165056ERL -6 - 5/16 AN to tubing connectors Male end
    2 EAR-165006ERL -6 - 3/8 AN to tubing connectors Male end

    2 RUS-658490 1 ft sections of pre assembled 5/16 Steel braided hose with female ends

    Simply attach one 5/16 to -6 tubing connector to the fuel rail on the intake manifold
    Then attach the 3/8 to -6 tubing connector to the return line on the fuel rail on the manifold the above PN#ís are from Summit Racing

    Cut the fuel ďtubingĒ about 6 inches below the firewall and follow the same steps as above. Now attach the hoses to the fittings which are now on the tubing. MAKE SURE the fittings are on snug! Now when the time comes to hook up the lines simply screw on the lines to the manifold.
    Note: be sure to label the lines, Fuel and return. Fuel being the larger line and the return the smaller in diameter.

    Oil cooler: most 6.0ís come with a oil cooler stock from the factory, this is not needed so you can buy the block off plate that comes on the v8 engines. The oil cooler lines will connect right above the oil filter on the block. You can get this part from your local dealer for a few bucks, be sure to get the gasket as well.

    Well thatís it, other than the above you just need to know how to pull a motor and how to put one back in! which can be found here. Engine Remove and Install

    Good luck and if you have any questions or comments about this thread Post up!

    6.0 swap - TR224 112 lsa - 918 springs -7.4" comp pushrods- LS2 timing chain -Walbro 255LPH intank- Pacesetter LT's - Custom Y-pipe with Quickflow muffler - LS1 E-Fans - 160 stat - Nelson Tuned - Fuddle 3K stall - FLT4l65e w/ Vac MOD - DJM 4/6 - Doetsch Drop shocks

  2. #2
    love the post. saved me a million headaches. thanx keep this at the top of the list people.

  3. #3
    DBYRD Guest
    pretty much covers it all. if ur doing the 4.3 to 6.0 swap id also recommend a new rearend as well. very nice write up and im glad u did this derek. this will save a bunch of people a lot of time scratching their heads like i did for a long time. its a great swap especially when u go from being one of the slowest to the one of the fastest and spend a lot less money getting there. i would recommend anyone that wants to do this swap read this post first THEN ask questions cuz it doesnt leave much to imagine cuz it covers the subject well. great job derek. i would even sticky this at the top admins.

  4. #4
    I would also recommend a new rear end. Also, just too add, I still have my stock tranny with almost 70,000 miles and its still working.(knock on wood) I guess it depends on how bad you beat it. Mine has been working fine, i don't go much to the track, but on the street i give it a beaten hehe.
    03' Silverado RCSB H/C 5.3, 4L80,76mm KBracing Kit
    13' Sierra Denali 2500HD CCSB 4x4

  5. #5
    Join Date
    Nov 2003
    Denton Texas
    I must have missed this one first time around. Pinned.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  6. #6
    Join Date
    Apr 2006
    You might want to fix one thing though, if you've got a 99-02 you can't use the '03+ harness. You'll have to switch to a cable throttle, or find an DBW 00-02 harness, which is not an easy find.

    And the V6 mounts can be made to work, but you'll need a 5/8" spacer for each side, and longer bolts. However, it does move the motor/tranny back a bit. I had to slot my rear tranny/crossmember holes a little. It wasn't back enough that I've had any driveshaft issues though.

    I ran into this problem when I did my swap. Contrary to what I was told, it won't work, so I'm attempting to recover some of my money by selling the leftover parts.

    Out of curiousity, what did you do about the AC lines/compressor? Did you re-use the V6 one?
    '99 GMC RCSB
    3" Body lift, 4" Rancho lift, Fox shocks
    36" BFG All-terrains
    LQ9 6.0L swap, gt2-3 cam, longtubes, LS1 fans, Nelson Performance tune
    4.8 gears/Eaton posi
    Built 4l65e
    Custom paint, roll pan, filled tail lights, relocated tail gate handle

    Future mods:

  7. #7
    A rearend is a great idea, I holded off on mine for a month or two. I mainly tried to point out what is required, a rearend is not required and i doubt your going to break the open diff, i couldnt do it lol! I pulled a 1.9 on the one wheel peel with a pair of ET streets. But like stated above i would swap one out whether it be during the swap or after it.

    It says if you have a 99-02 get that harness and if you have an 03+ get that harness.

    I personally would just buy new mounts, that way everything will be to factory specs and the engine will not sit higher etc. The price on the mounts really do not justify going through the trouble of trying to get the v6 mounts to work.

    Also like stated above you will need V8 lines such as the AC, Heater hoses, radatior hoses. I would go to a junk yard and pull the hoses off that you need, this way it wont cost much at all.

    as for as time i did the swap in a weekend. I Installed a cam in the 6.0, removed the stock tranny and pulled the v6 out on day 1 on day 2 I did the install of ot all!

    Thank you all for your comments!

    If anyone has any specific questions regarding the swap please post it up!

    6.0 swap - TR224 112 lsa - 918 springs -7.4" comp pushrods- LS2 timing chain -Walbro 255LPH intank- Pacesetter LT's - Custom Y-pipe with Quickflow muffler - LS1 E-Fans - 160 stat - Nelson Tuned - Fuddle 3K stall - FLT4l65e w/ Vac MOD - DJM 4/6 - Doetsch Drop shocks

  8. #8
    Join Date
    Sep 2005
    Austin Tx.
    When taking the 4.3 motor mounts off, and installing the 4.8/5.3 mounts, is there any cutting, grinding, or welding that needs to take place? Or is it simply bolts only?

    I have some questions about the fuel lines, but Ill wait to get some pictures up. Well I'll just explain it first without the pictures, and if its still unclear, then I will post pictures. I have the COMPLETE fuel rail assembly from front to back from a 2001 Ext Cab 5.3. Will anyone of this work. When I mean complete, I mean I got it from the dealership for like $230 bucks.

    Lastly, on a scale of 1-10. How hard is the swap from a 4.3 to a 5.3?
    1951 3100
    1984 C10

  9. #9
    Join Date
    Dec 2006
    i did a 4.3 to 5.3 swap it wasnt hard at all. motor bolted up to the transmission ( 4l60e) the exhuast ( stock ) bolted up the only problem i ran into was the mounts i used the passenger side mount from the 4.3 and used a 5.3 mount for the driver side had no problems..as for the fuel lines i cut the 4.3s and used flex hose to the 5.3 fuel lines..
    Simple: 408 on steroids!
    single digits coming soon!

  10. #10
    The 4.8/5.3 mounts bolt right in, no need to cut/weld etc.

    they lines may be too long, but im sure you can make them work.

    6.0 swap - TR224 112 lsa - 918 springs -7.4" comp pushrods- LS2 timing chain -Walbro 255LPH intank- Pacesetter LT's - Custom Y-pipe with Quickflow muffler - LS1 E-Fans - 160 stat - Nelson Tuned - Fuddle 3K stall - FLT4l65e w/ Vac MOD - DJM 4/6 - Doetsch Drop shocks

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