Gear ratios

[Bradleyworld]

I've got a 70 Chevy shortbed, fleetside 4x4.

When I had the rear differential rebuilt, I was told I had 373 gears and they were considered "highway gears"

I'm running a 2001 ZZ4 Corvette motor from GM, with 33 inch tires......Are these gears too high for this application?

The motor never seems to run at its optimum RPMs.

Looking for some input, good or bad.

Thanks, Bradleyworld

[Destructo]

Do you have an OD transmission in it? If not the 3.73 gears are probably good. I have 3.42 gears and can't use Overdrive right now because 3rd gear only turns about 2200 rpm on the highway and I get about 16mpg like that.

With a 1:1 transmission ratio, 3.73 gears, and 33" tires you should be turning about 2400-2500 rpm which is good for fuel economy depending on your engine setup.

[Bradleyworld]

Nope, no overdrive. I'm sure I could never use it if I did.

I don't have a tach(I know SHAME ON ME!) but it does seem to lug a little.

Thanks, Bradleyworld

[1FaastC10]

3.73s and 33s are just about perfect for each other. also, the ZZ4 is not a Vette motor, its a GM crate engine that was never offered in any production vehicle.

[Mudder]

3.73's and 33's are good to go

[Bradleyworld]

Thanks all.

Bradleyworld

[JIMs70GMC]

Of course from the factory the 3/4 tons had 4.10s and 4.56s with tires smaller than 33". My 70 has 4.10s and 33s and it keeps the RPMs up. My 71 has 4.56s and small 35s, not on the road yet, but the engine will be screaming soon! You could probably go w/ 4.10s and raise your RPMs a little. that ZZ4 will probably like it, turning about 2800 on the highway.