My set up is this....
5.3 stock long block(for now)
BTR Stg 3 truck cam 218/224 .553
4l80e 4000 stall
3.42 gear(going to 4.10 soon?)
Rcsb
Nx wet kit
Kit comes with 70mm. Was looking at the 78/75 upgrade option. Goal is 600ish whp.
My truck might get heads and intake before a turbo happens due to it being a project vehicle for an online webzine. I am sorta knowledgeable about boost but I would appreciate any input from the pros on here. Thank you.

 

It could possibly be done with a 70 but the 78 is definitely the better choice. 4000 stall and a wet kit makes the bigger turbo by far a better option especially considering your goal of 600.

 

That was my thought too. Also that would give me a little room above 600 hp if I wish

 

I would say the 76 mm unit. I have the 78 currently on my personal rig and am NOT impressed. I may put a 76 unit on it instead. I have built 2 similar 6.0 motors, and a 5.3 also with both the 76 and 78 turbos. The 76 is more responsive and I dont think you could tell a difference in power up top otherwise. Bigger isnt always better IMO. If you have a super loose converter the 78 would spool just fine. Error on making it more drivable.

 

So upgrading to the 76 (with ceramic bearings?) would be the better option? I do daily drive my truck

 

For the price difference i vote go big and have room to grow.

 

IMO, going "big with room to grow" on a turbo build is the biggest single mistake people make in a turbo build. Put the right turbo on it for what you have NOW and it will be the best it can and for most people, that's good enough! lol

Turbos are not that expensive and have good used resale value. So upgrading later when (if) you do need bigger, it's not that much money to upgrade the turbo it's self.

 

What would you recommend?
My thought is also if I can make the same power with a 78@8psi as a 70@14psi I would pick the larger. My last turbo car was in 1997 so I'm rusty lol

 

My advice, go with a USA made product over china junk

Borg S366 or S472 in T4 would be excellent choices.

You didn't state what your intended purpose for the truck was

 

I went with the 70mm. My goal is 600 rwhp at around 16 psi or so before its maxed out, 93 octane, and meth. Might not make it to 600 but should be close enough. Plus I want good spool for street driving. I am looking for something fun to drive and come into boost quick. Once I get the feel for that and want more, I'll focus on making more power and running faster times and get a Borg. I'm sure I'll have traction issues with the 70mm anyways.