4.3 to 4.8 or 5.3

[mcdad1979]

i have a 05 4.3 5spd im wanting to do a 4.8 or 5.3 swap. my question is i know gm never put a nv3500 behind the 5.3 and i know it will not hold up to the abuse of the 5.3 for an extended period of time but is there parts available to hook my nv3500 to the 5.3?

[00_Silverado_Z71]

Considering a 4.8 is exactly the same motor as a 5.3 other than some internals in the motor itself yes they will go together I'm using my nv3500 off my 4.3 and it is now attached to my 4.8 i just had to get a 4.8/5.3 flywheel and the new larger clutch for the v8. why do you assume the 5 speed was never put behind a 5.3 if they used the same exact nv3500 behind 4.8s?

[mcdad1979]

everybody i have talked to says gm never used the nv3500 behind the 5.3 cause the engine produced to much torque for that trans.

[johnmichael397]

i have a nv3500 behind my lq4 and it seems to be holding up fine. But mine was behind a 350 before if that makes a difference.

[Frenchy]

In '99 the 5speed did go behind the 5.3. Very rare though. You'll need a flywheel and clutch for a 4.8 5speed truck. I used a Centerforce clutch. My truck started 4.3 5speed too. Now it's a 5.3

[mcdad1979]

thanks for the info i will for sure be doing the 5.3 now. one more question if i get the ecm from the donor truck will i still need to get the ecm reprogrammed for my truck?

[00_Silverado_Z71]

You can do either one get the one from the donor truck or reprogram yours I would say

[mcdad1979]

now which wiring harness will i need to use. will i have to find a v8 5spd harness or can the v8 automatic harness work?

[Frenchy]

V8 auto harness already has everything there for the clutch switch etc. You need to cut the back up light pigtail off the 4.3 harness and splice it into the automatic harness. You can then remove absolutely everything automatic trans related if you'd like. Or just tie it out of the way. VSS plugs right in. Then get a tune for the 5speed truck so it's not looking for the PRNDL switch and you're good.

[mcdad1979]

thanks for all the help Frenchy.