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Rear ends Andy 1-3-04  
Right now my Crown has a 4.68 ratio rear end and I want to improve my milage and top speed. The lowest ratio I've seen is 4.11. Although this would help it isn't the increase I want. Is it possible to find something around 3.75 or do I need to go for the 4.11 and change my 24" tires to 26"?
I have a Cummins 220 with a turbo added (should be about 262hp now) and a Roadranger 10 speed.
Re: Rear ends Brent DeGreene 1-3-04  
It might be easier to find a Road Ranger with overdrive. The ten speeds were built with top gear overdrive and top two overdrive although I believe the top two units were all heavier duty.

I have the same problem with top speed in my Crown although I don't know the axle ratio. It tops out at 62 mph but already gets 10 mpg.
Re: Rear ends Aaron 1-7-04  
Gents, about the worst thing you can do is to gear the busses high,the small bore's need to be run at 1900 to 2100 rpm not lugging along at 1650.Thats why these busses were geared low so that the motors were wound up most of the time.Low rpm or lugging is not good for these as they will start breaking piston skirts and creating hot spots on the liners.
Re: Rear ends Mark O. 1-10-04  
Changing the 11X20 tires to 12X24.5 tires increased my top speed more than 5 MPH in my 262 powered Crown.

We can now cruise easily at 70 MPH at 1900 RPM. It hasn't made an appreciable difference in the hill climbing ability of fuel mileage.

Your fuel mileage won't change very much regardless of what you do with the rear end ratios. It takes a certain amount of fuel to move the bulk and the weight down the highway and through the air.

What ever you do, install a pyrometer. With a 2-cycle DD you can get a pretty good idea of how hard it is working by the water temp and the oil pressure--high water and low oil means it is time to shift down. With a Cummins, by the time you start to notice those two changes you will most likely have melted down a piston. With a higher speed rear end, you will reach melt down temps much faster.

Good luck and happy trails.

Mark O.
Re: Rear ends Jared 1-13-04  
I believe you guys all forgot to mention that you're referring to diesel engines, whereas my gas powered ford 429 will run anywhere through it's whole range of rpm all day long.

Still looking for a 2 speed axle for my bus as i've got a ratio somewhere near 6.91 to 1, which tops out my bus at 55mph, i need more speed. Anyone got one to spare?? LOL

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