As we speak my 85' K20 Chevy Pickup is getting body work done, and painted. At that point the truck will be how I want it appearance wise, so the next step is the drivetrain.

I want to pull the 350/700R4/208 in favor of a LSx drivetrain, but I don't want to do the simple 6.0/4L80e dropout swap. I talked it over with a few buddies, and I really want to throw a turbo kit into the mix. Ive been wanting to do a turbo build for the last year, but I only know the basics when it comes to turbo's and I feel the truck would be a great way to get my hands dirty with some boost. My truck's engine bay has a ridiculous amount of room, and I can afford for it to be down for a few months. My TA on the other hand is my daily driver.




The goal is very modest boost on a stock bottom end 6.0. Say 6-8lbs of boost. Don't really have a HP goal in mind really. I have been doing as much reading and researching as I can, but this build is pretty different than any I have came across. The truck has 37" tires (Next set will be 40"s), and I do haul with it and will occasionally tow with it. It currently has 4.10 gears, and I didn't plan on going deeper until I swap a 1 ton front differential in but maybe the 4.10s are good for a turbo motor?

Now my questions:

I do haul/tow. What would be a safe stall speed to run?

Are the 4.10s good for a turbo motor?

What size/brand turbo? I've been told a MP70 wouldn't be a bad choice, and will spool fast.

I can get ahold of LS2 GTO factory manifolds off a buddy. Will those work just as well as truck manifolds?

Keep factory cam, or upgrade? If upgrade, what kind of specs for a turbo build with 37" tires and towing/hauling in mind?

I'd like to run A/C. Do I have wishful thinking?



I have other questions, but those are the main ones for now.

 

You won't need much stall with a turbo, I believe Circle D has one for the 80e trans around a 2800 stall.

Typically with 40" tires, you would almost need deeper gears, but with a turbo, I think it would love it. Turbos like to have load, lower gears (numerically) provide more load.

I'll be using the MP70 on my 4.8, anything in the 70-76 mm range should meet your goals.

Stock cams work. aftermarket cams make more power just like naturally aspirated. I'm no cam expert so I won't recommend one.

GTO manifolds should work if you have the room.

A/c should be fine as long as it clears any hot or cold side piping.

 

^great info there, If the LS2 GTO manifolds are like the LS1 GTO manifolds then I wouldnt run them. They are retardedly routed and big. Im running LS1 camaro manifolds flipped up on mine but LS3 camaro manifolds flipped forward and down work really well, we are using them on my roommates twin turbo 02 camaro. He doesnt have A/C so that may be a problem there. I know with my setup I could still run A/C but I dont. You can also buy a used trick performance or KB log setup. I also think the 4.10's will work just fine with your setup and I would go with a TH400 if I were you. And as far as stall, Circle D is where its at, especially for TH400's

 

I would run the 4.10's and see how you like them before you start replacing everything. I would go with a bigger turbo than the mp 70mm...

 

Yes I was thinking in the 2400-2800 range for a stall.

With 37" tires it brings my 4.10 gears to around 3.08s. Now a turbo will probably like that, but will it like towing my TA? I would assume if I bump up to 40" tires I will most definitely need to regear to atleast 4.56s.

For my goals a stock cam will probably work, but if the money is there I may upgrade it at the same time.

Now what about those ebay turbo manifolds I've seen people talking about. Are they worth the money?

I don't want to run a 3spd so a TH400 is out. I do plan on running a 4L80e which is just as strong tho, and gives me the overdrive I want.

I agree. I didn't plan on regearing until I swapped in a Dana 60 front differential. At that time I can regear if needed, or leave the 4.10s in until I move up to 40" tires in a few years.

 

Ive heard good things about those eBay manifolds so I would say go for it! I would reconsider the TH400. I've seen cases where a 400 would hold when several different 80s couldn't. Also with 40" tires and 4.10s you could prolly cruise at 70 @ 2500 rpm or so.

 

I would say something like this would work better with twins.

 

everything is better with twins!

 

That's an excellent point you bring up, and it's something many turbo truck guys forget. You have a 6.0, will have a tight stall, pushing a lot of weight, and spinning very heavy tires. I doubt you will have any issues spooling a small 70-76mm turbo if the truck is geared correctly for the tire size. With an OD trans, I suggest 4.88's for 37's and 5.13's for 40's.

 

If I do this turbo project it won't be being beat on as much as you might be thinking lol. I think I'll be fine with a 4L80.

I'm all ears. What is your reasoning for going with twins?


After some more research I agree with your gearing advice. I won't be towing anytime soon, so I'll probably wait til I swap in a Dana 60 1 ton front differential before I regear.