Changing Gear Ratio in 66 Chevy C30

[kuzco]

Hi,

I'm changing the gear ratio in my 66 Chevy C30 long bed stepside, I also am going to put a 305, 327, 350, or 396 motor in it (haven't decided yet), and a 5 speed transmission, with 17 inch tires on the rear end and 15 inch tires on the front end, it's 2wd, I was curious which gear ratio may be better for my setup, I'd like decent mpg but some power as well (I won't be towing with it) The gears I can choose are:

3.54, 3.73, 4.10, 4.56, 5.11.

Thanks.

[rideblue00]

What kind of 5 speed? If it has overdrive, then you can stay around 3.73. The S10 T-5 5speed isnt rated to take much abuse from a V-8.

[Captainfab]

So apparently your '66 C30 has a Dana 60 or 70 rear end instead of the typical Eaton HO52/72? To determine the optimum gear ratio, you will need to know the outside diameter of the rear tires you will be running, not just the rim diameter. Then you will also need to decide just which transmission you will be running. This will give you the OD ratio for the trans, which is needed to calculate the correct gear ratio. Just as a wild guess, I would say either 3.73's or 4.10's....probably more likely the 4.10's. The engine you choose should be considered also. A big block (more torque) will tollerate a taller gear than the 305 you mentioned.

[factorystock]

Originally Posted by kuzco

Hi,

The gears I can choose are:

3.54, 3.73, 4.10, 4.56, 5.11.

The C 30 was designed for heavy loads, so most had 5 .14 gears or the optional 4.57's. Assuming this is still too low, a 4.10 ratio was offered on C 30's from 1969 to 1972. Find a 4.10 HO 72 pumpking out of a V8 or big block 69 thru 72 C 30, for the most cost effective upgrade. Any other axle ratio or transmission change will require mucho work and $$$.

[kuzco]

Alright, I had talked to my friend who convinced me to leave the C30 alone and go with a 65 GMC with automatic and a better rear end.