K30 gear ratio

[Fuelster]

I am building a 86 K30. Seem to have a lot of housings front and rear with 4.56 gears. I was hoping for 4.10s. I am putting a 454HO crate engine in it with a 4L80E with a divorced NP205 or a Divorced Rockwell 221 T Case. What do you all think about running the 4.56 gears in this truck? Not an off road rig for sure. 235/85/16 tires on it. I am thinking about highway rpms.

[geezer#99]

Punch your numbers in here.
http://www.advanced-ev.com/Calculators/TireSize/

About 250 rpm difference at 70 mph between ratios.

[wilkin250r]

4.10 still sounds like a low ratio, expecially with a big block.

I don't know what kind of highway speeds you're looking to run, but I used to have a nice 1972 C10 with 4.10 gears, and a 350/350 combo. My tires were just a little smaller, I think I was running 31 inch tires while you're looking about 32, but I was screaming RPMs at highway speeds. It was geared low because it originally built as a camper-special, but with the camper weight off it became a sports car (to a teenager), it launched off the line. I loved that truck.

You've got overdrive, I think that will help with highway RPMs, but that 454 should easily be able to push much taller gearing.

What are you looking for from this truck? Heavy towing, max 65mph speeds?

[MTCK]

It will be snappy with the big block, 4L80e and 4.56 gears, but much faster than 65mph and you will wish you had shorter gears. Oh and it will pull a house down. If you're cruising I'd try to find 4.10 or even 3.73. Mine pulled a heavy trailer pretty well with those gears and a tired TBI 350, so if you are going to work it and drive slow, great setup.

[bilfman]

I have done this very swap and for sure would not do 3.73. I have 3.73's and when towing or using my slide on camper the additional 10% of running 4.10's would be great. I wouldn't even be opposed to 4.56's . With 3.73's I am about 1700 rpm at 60. Keep in mind the carrier in the Dana's change when going above 4.10. So that may help make your decision as well.