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Running Gear


Charter Member
SM 2003
Full Member
Feb 27, 2002
Twin Cities, MN
I would like a good explantion of the difference between the 4.10 and 3.73 running gear. I've heard the details before but many of you are indicating the 4.10 gearing.

Thanks - Jamie
3.73 or 4.10 are simply the gear ratios in the differentials (Ex: the drive shaft turns 3.73 revolutions for each revolution of the axle). With a 4.10, the engine turns more revs at a given speed than a 3.73. This gives better accelleration, more trailering capacity, etc.
So a 3.73 would get better mileage as a side-effect of turning less RPMs at say 70? Whereas a 4.10 would have more RPMS at any speed therfore more torque earlier in the curve?
Gas mileage will be very close though.

As gas usage is based on Hp required.

Most engines have a Fuelper hp-hour rating when buying industrial engines. The constant is different for each RPM so they have curves. For industrial diesels it is about .3LBS of fuel per HP per hour at 2100 RPM.

Hp required is based on how fast you want to go and the inefficeincies of the driveline and engine. Ancillary equipment drains and wind resistance as well. Since the higher gears require less torque from the engine at a given speed then the Hp draw is less but since it operates at a higher RPM the fuel constant may be lower. Kinda negates itself.

That said the mileage will be so close one stomp of the pedal will null any savings with the lower gears.

Kinda geeky huh?
Thanks all for the input. I guess I was starting to feel cheated since mine loaded Z-71 came with the 3.73.
How do I find out if i have the 3.73 or the 4.10 on my Z-71? I never saw a complete equipment list for it.....
ygmn . .

but don't frictional losses go up at a rate related to RPM as opposed to torque? ?Hence higher RPM will tend to hurt gas mileage even though output HP is the same.

Isn't that the theory as to why overdrive transmissions improve gas mileage, and why the 'Vette has the absurd 1-4 shift at low accelleration rates and a uselessly tall 6th gear - all in the name of improved gas mileage and CAFE numbers for GM?

Internal engine friction, water pump oil pump etc at higher RPMs do increase Hp draw.

These curves kinda start low and raise up. This said there is a ultimate spot where the engine will get the best fuel economy based on HP available and fuel consumption rates per Hp.

Here is a link to a spec page on a Caterpiller 3412E 1000Hp engine which has electronic fuel management system. Scroll through and on the second page is a fuel consumption curve. This one lists the fuel in Gal per hour.

I guess what I was trying to say is the fuel savings with the lower gears is not that significant versus the pulling power you will feel in your seat.

You can see all of your truck's RPO (Regular Production Options) codes on a sticker inside your glovebox....Yeah you have to take everything out to see the sticker. :eek:

If you find a GT4 code it is a 3.73 Rear Axle
If you find a GT5 code it is a 4.10 Rear Axle

Hope that helps : :D