10 Bolt HP Rating with 4.10 Gears?

[Mike21]

I have an 85 k10 SWB I am restoring it had the 305, th700R4, NP203 and 10 bolt axles with 3.73. I am planning 325-400 HP with a built 700R4 and I plan on a lift and 35in tires. Thinking 4.10 or 4.56 gears. Can a 10 bolt handle this? What upgrades are out there? While on the subject, anyone know what a NP203 can handle?

 

[Turbo4whl]

Lower gears like the 4.56:1, push back less on the forward drive line i.e. the trans and transfer case. Taller gears like the 3.07:1 push harder on the forward drive line.

The 4.56:1 gears will push harder on the axle shafts in the rear. These may want an upgrade with large tires.

 

[Curt]

That power level isn’t a problem.It’s that power level with 35” tires.(10 bolt)Alloy shafts will help,but the ring gear and bearings won’t like it.8.5 ring gear is rather thin at 4.56.C-clip axle.Lose then shaft,lose the tire.

NP 203 will handle it,supposing it’s in good shape.

Automatic is more forgiving than manual.

 

[Curt]

Wait,the 203?Sure it’s not a 208?208 will handle as well,so I guess it don’t matter.

NP203 is 170lbs vs 85lbs of the NP208.It might matter

 

[Turbo4whl]

Wait,the 203?Sure it’s not a 208?208 will handle as well,so I guess it don’t matter.

NP203 is 170lbs vs 85lbs of the NP208.It might matter

Right. 1985 would not have a 203 unless someone swapped it in.

 

[Curt]

Ya,that doesn’t make a lot of sense,but stranger things have happened.Swap in a rear 3/4 ton 14 bolt with a 10 1/2” ring gear and it won’t be a issue.

You can find them pre 80’ 3/4 ton trucks and vans.43 1/2” from perch to perch.You’ll have to run 16” wheels,a little driveshaft work.

 

[Mike21]

Ok Il go verify the TC. I was most likely incorrect as my TC is a stock 1985 so its probably the 208.

 

[Mike21]

Yes my mistake its a NP 208. That being said, sounds like it cant withstand 325-400HP? What is a good upgrade that will fit?