rear end gears

[Bill76]

Put in a 3.55 , good all around gear.
I put 4.30s in my brand new 68 runner , the engine screamed on the hi way but with slicks on the back I won darn near every street race.

 

[209gtx]

My car is on the road after all theses years. The engine is a 383 completely rebuilt and the rebuilder figures 330 to 350 HP. I have a open 8 1/4 rear with 2 something highway gears.
I had the car on the highway and had it up to maybe 55-60 and it felt like the engine was at a fast idle, it just cruised along with no effort. It felt strange as I hardly was pressing on the gas pedal
I have a sure grip 355 rear that will be rebuilt shortly and I wanted to install it in this car.
My question is would I be better with changing the gears to 3:23? The current rear is the only component I didn't rebuild or even inspect in detail so I figured id use the sure grip and rebuild that and I don't mind the added expense of a new ring and pinion.
Any opinions are welcomed and appreciated

if you go to expense, and your sure you have a 8.75 get a complete diff pumpkin from DR DIff or moser, and have them install a true trac !

 

[209gtx]

Put in a 3.55 , good all around gear.
I put 4.30s in my brand new 68 runner , the engine screamed on the hi way but with slicks on the back I won darn near every street race.

I also run 4.56 8.75 on freeways during hot augsut night in reno nevada and also bracket race with Hoosiers and MT

 

[Darter6]

This week I pulled the 4.10's out of the 65 and installed 3.23 with a tru-trac. Runs nice at 60 MPH now and can run with the freeway traffic without the engine screaming.

 

[AJ/FormS]

A small-cam 383 has plenty of down-low torque . I wouldn't be in a hurry to swap out what you have. Verify your speed-O is accurate, then give those gears a chance.
2.94s make about 2370rpm@65mph@zero slip with 27" tires
3.23s make about 2610
3.55s make about 2870
The difference is about 10% per ratio. The fuel economy difference might be half that.
Dig off the line will also translate to ~10% more power.
But you can get the same 10% extra dig with a lil more TC stall.
So if your current TC is flash stalling around 2400, and you like the 2.94s but she lacks dig, just up the stall to whatever rpm gets you 10% more footpounds. For 2.94s that creates a bit of a dilemma as to economy. If you swap to say a 2800TC to get the dig, but the hiway-running rpm is 2400, then the TC will be slipping perhaps 300rpm which is 11% , so you really didn't gain anything, over just installing 3.23s.
It works better the other way.
For instance; the 3.23s will like up to 2600 stall, and the 3.55s up to 2900.
This keeps them coupled better at hiway speeds. Which produces less heat and so on.
But for a mostly city-car, a 2800Tc is gangbusters with 3.23s.
And not too shabby with 2.94s and a hi-torque 360 cuber.
I love that 2800

 

[Darter6]

Exactly, I pulled the 3500 converter out and went with a 2500/2800 from TCI.Works well with the 3.23's.